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Platform Interface Specification

This document specifies the interface between a lifecycle and a platform.

A platform orchestrates a lifecycle to make buildpack functionality available to end-users such as application developers.

Examples of a platform might include:

  1. A local CLI tool that uses buildpacks to create OCI images
  2. A plugin for a continuous integration service that uses buildpacks to create OCI images
  3. A cloud application platform that uses buildpacks to build source code before deployment

Table of Contents

Platform API Version

This document specifies Platform API version 0.15.

Platform API versions:

  • MUST be in form <major>.<minor> or <major>, where <major> is equivalent to <major>.0
  • When <major> is greater than 0 increments to <minor> SHALL exclusively indicate additive changes

Terminology

CNB Terminology

A buildpack refers to software compliant with the Buildpack Interface Specification.

A base image is an OCI image containing the base, or initial set of layers, for other images.

A build image is an OCI image that serves as the base image for the build environment.

A run image is an OCI image that serves as the base image for the app image.

The build environment refers to the containerized environment in which the lifecycle executes buildpacks.

An app image refers to an OCI image generated by the lifecycle by extending the run image with any or all of the following: app layers, launch layers, launcher layers, image configuration.

A launch layer refers to a layer in the app image created from a <layers>/<layer> directory as specified in the Buildpack Interface Specification.

An app layer refers to a layer in the app image created from the <app> directory as specified in the Buildpack Interface Specification.

A run image layer refers to a layer in the app image originating from the run image.

A launcher layer refers to a layer in the app OCI image containing the launcher itself and/or launcher configuration.

The launcher refers to a lifecycle executable packaged in the app image for the purpose of executing processes at runtime.

An execution environment refers to the context in which an application is intended to run. Standard values include "production", "test", and "development". Production is the default if not specified. The value MUST NOT contain the character / as it is reserved for future use.

An image extension refers to software compliant with the Image Extension Interface Specification. Image extensions participate in detection and execute before the buildpack build process.

A stack (deprecated, see deprecations) is a contract, implemented by a build image and run image, that guarantees properties of the build environment and app image.

Additional Terminology

An image reference refers to either a tag reference or digest reference.

A tag reference refers to an identifier of form <registry>/<repo>:<tag> which locates an image manifest in an OCI Distribution Specification compliant registry.

A digest reference refers to a content addressable identifier of form <registry>/<repo>@<digest> which locates an image manifest in an OCI Distribution Specification compliant registry.

The following is a non-exhaustive list of terms defined in the OCI Image Format Specification used throughout this document:

The following is a non-exhaustive list of terms defined in the OCI Distribution Specification used throughout this document:

Build Image

A typical build image might determine:

  • The OS distro in the build environment.
  • OS packages installed in the build environment.
  • Trusted CA certificates in the build environment.
  • The default user in the build environment.

The platform MUST ensure that:

  • The image config's User field is set to a non-root user with a writable home directory.
  • The image config's Env field has the environment variable CNB_USER_ID set to the user †UID/‡SID of the user specified in the User field.
  • The image config's Env field has the environment variable CNB_GROUP_ID set to the primary group †GID/‡SID of the user specified in the User field.
  • The image config's Env field has the environment variable PATH set to a valid set of paths or explicitly set to empty (PATH=).

The platform SHOULD ensure that:

  • The image config's Label field has the label io.buildpacks.base.maintainer set to the name of the image maintainer.
  • The image config's Label field has the label io.buildpacks.base.homepage set to the homepage of the image.
  • The image config's Label field has the label io.buildpacks.base.released set to the release date of the image.
  • The image config's Label field has the label io.buildpacks.base.description set to the description of the image.
  • The image config's Label field has the label io.buildpacks.base.metadata set to additional metadata related to the image.

Run Image

A typical run image might determine:

  • The OS distro or distroless OS in the launch environment.
  • OS packages installed in the launch environment.
  • Trusted CA certificates in the launch environment.
  • The default user in the run environment.

The platform MUST ensure that:

  • The image config's Env field has the environment variable PATH set to a valid set of paths or explicitly set to empty (PATH=).

The platform SHOULD ensure that:

  • The image config's User field is set to a user with a DIFFERENT user †UID/‡SID as the build image.
  • The image config's Label field has the label io.buildpacks.base.maintainer set to the name of the image maintainer.
  • The image config's Label field has the label io.buildpacks.base.homepage set to the homepage of the image.
  • The image config's Label field has the label io.buildpacks.base.released set to the release date of the image.
  • The image config's Label field has the label io.buildpacks.base.description set to the description of the image.
  • The image config's Label field has the label io.buildpacks.base.metadata set to additional metadata related to the image.
  • The image config's Label field has the label io.buildpacks.rebasable set to true to indicate that new run image versions maintain ABI-compatibility with previous versions (see Compatibility Guarantees).

Target Data

For run images, the platform SHOULD ensure that:

  • The image config's Label field has the label io.buildpacks.base.id set to the target ID of the run image.

The target ID:

  • MUST only contain numbers, letters, and the characters ., /, and -.
  • MUST NOT be identical to any other target ID when using a case-insensitive comparison.
  • SHOULD use reverse domain notation to avoid name collisions - i.e. buildpacks.io will be io.buildpacks.

For both build images and run images, the platform MUST ensure that:

  • The image config's os and architecture fields are set to valid identifiers as defined in the OCI Image Specification.
  • The build image config and the run image config both specify the same os, architecture, variant (if specified), io.buildpacks.base.distro.name (if specified), and io.buildpacks.base.distro.version (if specified).

The platform SHOULD ensure that:

  • The image config's variant field is set to a valid identifier as defined in the OCI Image Specification.
  • The image config's Label field has the label io.buildpacks.base.distro.name set to the OS distribution and the label io.buildpacks.base.distro.version set to the OS distribution version.
    • For Linux-based images, each label should contain the values specified in /etc/os-release ($ID and $VERSION_ID), as the os.version field in an image config may contain combined distribution and version information.
    • For Windows-based images, io.buildpacks.base.distro.name should be empty; io.buildpacks.base.distro.version should contain the value of os.version in the image config (e.g., 10.0.14393.1066).

Compatibility Guarantees

  • Base image authors SHOULD ensure that new build image versions maintain ABI-compatibility with previous versions, although violating this requirement will not change the behavior of previously built images containing app and launch layers.
  • Base image authors MUST ensure that new run image versions maintain ABI-compatibility with previous versions.
  • Base image authors MUST ensure that app and launch layers do not change behavior when the run image layers are upgraded to newer versions, unless those behavior changes are intended to fix security vulnerabilities.

Lifecycle Interface

Platform API Compatibility

The platform SHOULD set CNB_PLATFORM_API=<platform API version> in the lifecycle's execution environment.

If CNB_PLATFORM_API is set in the lifecycle's execution environment, the lifecycle:

  • MUST either conform to the matching version of this specification or
  • MUST fail if it does not support <platform API version>

Operations

Build

A single app image build* consists of the following phases:

  1. Analysis
  2. Detection
  3. Cache Restoration
  4. (Optional) Base Image Extension
  5. Build*
  6. Export

A platform MUST execute these phases either by invoking the following phase-specific lifecycle binaries in order:

  1. /cnb/lifecycle/analyzer
  2. /cnb/lifecycle/detector
  3. /cnb/lifecycle/restorer
  4. /cnb/lifecycle/extender (Optional)
  5. /cnb/lifecycle/builder
  6. /cnb/lifecycle/exporter

or by executing /cnb/lifecycle/creator**.

* Build is an overloaded term that refers to both a single phase and the operation comprised of the above phases. The meaning of any particular instance of the word build must be assessed in context.

**Does not perform image extension.

Rebase

When an updated run image is available, an updated app image SHOULD be generated from the existing app image config by replacing the run image layers in the existing app image with the layers from the new run image. This is referred to as rebasing the app, launch, and launcher layers onto the new run image layers. When layers are rebased, any app image metadata referencing to the original run image MUST be updated to reference to the new run image. This entire operation is referred to as rebasing the app image.

Rebasing allows for fast runtime OS-level dependency updates for app images without requiring a rebuild. A rebase requires minimal data transfer when the app and run images are co-located on an OCI registry that supports Cross Repository Blob Mounts.

To rebase an app image a platform MUST execute the /cnb/lifecycle/rebaser or perform an equivalent operation.

If an SBOM is available, platforms MAY:

  • Warn when a rebase operation would add OS packages.
  • Fail if a rebase operation would remove OS packages.

Launch

/cnb/lifecycle/launcher is responsible for launching user-provided and buildpack-provided processes in the correct execution environment. /cnb/lifecycle/launcher, or a symlink to it (see exporter outputs), SHALL be the ENTRYPOINT for all app images.

Usage

All lifecycle phases:

  • MUST read CNB_PLATFORM_API from the execution environment and evaluate compatibility before attempting to parse other inputs (see Platform API Compatibility)
  • MUST give command line inputs precedence over other inputs

analyzer

Usage:

/cnb/lifecycle/analyzer \
  [-analyzed <analyzed>] \
  [-cache-image <cache-image>] \
  [-daemon] \ # sets <daemon>
  [-gid <gid>] \
  [-insecure-registry <insecure-registry>...] \
  [-launch-cache <launch-cache>] \
  [-layers <layers>] \
  [-layout] \ # sets <layout>
  [-layout-dir] \ # sets <layout-dir>
  [-log-level <log-level>] \
  [-previous-image <previous-image> ] \
  [-run <run> ] \
  [-run-image <run-image> ] \
  [-skip-layers <skip-layers> ] \
  [-tag <tag>...] \
  [-uid <uid>] \
  <image>
Inputs
Input Environment Variable Default Value Description
<analyzed> CNB_ANALYZED_PATH <layers>/analyzed.toml Path to output analysis metadata (see analyzed.toml
<cache-image> CNB_CACHE_IMAGE Reference to a cache image in an OCI registry
<daemon> CNB_USE_DAEMON false Analyze image from docker daemon
<gid> CNB_GROUP_ID Primary GID of the build image User
<insecure-registry>... CNB_INSECURE_REGISTRIES When fetching images from this registry, do not use TLS encryption or certificate verification
<layers> CNB_LAYERS_DIR /layers Path to layers directory
<layout> CNB_USE_LAYOUT false (experimental) Analyze image from disk in OCI layout format
<layout-dir> CNB_LAYOUT_DIR (experimental) Path to a root directory where the images are saved in OCI layout format
<image> Tag reference to which the app image will be written
<launch-cache> CNB_LAUNCH_CACHE_DIR Path to a cache directory containing launch layers
<log-level> CNB_LOG_LEVEL info Log Level
<previous-image> CNB_PREVIOUS_IMAGE <image> Image reference to be analyzed (usually the result of the previous build)
<run> CNB_RUN_PATH /cnb/run.toml Path to run file (see run.toml)
<run-image> CNB_RUN_IMAGE resolved from <run> Run image reference
<skip-layers> CNB_SKIP_LAYERS false Do not restore SBOM layer from previous image
<tag>... Additional tag to apply to exported image
<uid> CNB_USER_ID UID of the build image User

-<image> MUST be a valid image reference

  • If the platform provides one or more <tag> inputs, each <tag> MUST be a valid image reference.
  • If <daemon> is false and the platform provides one or more <tag> inputs, each <tag> MUST refer to the same registry as <image>.
  • If <daemon> is false, <previous-image>, if provided, MUST be a valid image reference.
  • If <daemon> is true, <previous-image>, if provided, MUST be either a valid image reference or an imageID.
  • If <skip-layers> is true the lifecycle MUST NOT restore the SBOM layer (if any) from the previous image.
  • If <run-image> is not provided by the platform the lifecycle MUST resolve the run image from the contents of run or fail if run does not contain a valid run image.
  • The lifecycle MUST accept valid references to non-existent <previous-image>, <cache-image>, and <image> without error.
  • The lifecycle MUST ensure registry write access to <image>, <cache-image> and any provided <tag>s.
  • The lifecycle MUST ensure registry read access to <previous-image>, <cache-image>, and <run-image>.
  • The lifecycle MUST write analysis metadata to <analyzed>, where:
    • image MUST describe the <previous-image>, if accessible
    • run-image MUST describe the <run-image>
  • If <layout> is true, <layout-dir> MUST be provided and the lifecycle MUST resolve <run-image> and <previous-image> following the rules to convert the reference to a path
Outputs
Output Description
[exit status] (see Exit Code table below for values)
/dev/stdout Logs (info)
/dev/stderr Logs (warnings, errors)
<analyzed> Analysis metadata (see analyzed.toml
Exit Code Result
0 Success
11 Platform API incompatibility error
12 Buildpack API incompatibility error
1-10, 13-19 Generic lifecycle errors
30-39 Analysis-specific lifecycle errors

detector

The platform MUST execute detector in the build environment

Usage:

/cnb/lifecycle/detector \
  [-analyzed <analyzed>] \
  [-app <app>] \
  [-buildpacks <buildpacks>] \
  [-build-config <build-config>] \
  [-extensions <extensions>] \
  [-generated <generated>] \
  [-group <group>] \
  [-layers <layers>] \
  [-log-level <log-level>] \
  [-order <order>] \
  [-plan <plan>] \
  [-platform <platform>] \
  [-run <run> ] \
  [-system <system>]
Inputs
Input Environment Variable Default Value Description
<analyzed> CNB_ANALYZED_PATH <layers>/analyzed.toml Path to output analysis metadata (see analyzed.toml
<app> CNB_APP_DIR /workspace Path to application directory
<build-config> CNB_BUILD_CONFIG_DIR /cnb/build-config Path to build config directory
<buildpacks> CNB_BUILDPACKS_DIR /cnb/buildpacks Path to buildpacks directory (see Buildpacks Directory Layout)
<exec-env> CNB_EXEC_ENV production Target execution environment. Standard values: "production", "test", "development".
<extensions>^ CNB_EXTENSIONS_DIR /cnb/extensions Path to image extensions directory (see Image Extensions Directory Layout
<generated>^ CNB_GENERATED_DIR <layers>/generated Path to output directory for generated Dockerfiles
<group> CNB_GROUP_PATH <layers>/group.toml Path to output group definition
<layers> CNB_LAYERS_DIR /layers Path to layers directory
<log-level> CNB_LOG_LEVEL info Log Level
<order> CNB_ORDER_PATH <layers>/order.toml if present, or /cnb/order.toml Path resolution for order definition (see order.toml)
<plan> CNB_PLAN_PATH <layers>/plan.toml Path to output resolved build plan
<platform> CNB_PLATFORM_DIR /platform Path to platform directory
<run>^ CNB_RUN_PATH /cnb/run.toml Path to run file (see run.toml)
<system> CNB_SYSTEM_PATH /cnb/system.toml Path to system buildpacks file (see system.toml)

^Only needed when using image extensions

Outputs
Output Description
[exit status] (see Exit Code table below for values)
/dev/stdout Logs (info)
/dev/stderr Logs (warnings, errors)
<group> Detected buildpack group (see group.toml)
<plan> Resolved Build Plan (see plan.toml)
<analyzed> Updated to include the run image obtained from applying generated Dockerfiles
<generated>/run/<image extension ID>/Dockerfile Generated Dockerfiles (see Image Extension Specfication)
<generated>/build/<image extension ID>/Dockerfile Generated Dockerfiles (see Image Extension Specfication)
<generated>/build/<image extension ID>/<extend-config> Configuration for the extend phase (see Image Extension Specfication)
Exit Code Result
0 Success
11 Platform API incompatibility error
12 Buildpack API incompatibility error
1-10, 13-19 Generic lifecycle errors
20 All buildpacks groups have failed to detect w/o error
21 All buildpack groups have failed to detect and at least one buildpack has errored
22-29 Detection-specific lifecycle errors
91 Extension generate error
92-99 Generation-specific lifecycle errors

When <system> is provided (optional), the lifecycle:

  • SHALL merge the system.pre.buildpacks group with each group from <order> such that the pre buildpacks are placed at the beginning of each order group before running detection.
    • System buildpacks in pre SHALL NOT be merged if the group already contains a buildpack with the same ID.
  • SHALL merge the system.post.buildpacks group with each group from <order> such that the post buildpacks are placed at the end of each order group before running detection.
    • System buildpacks in post SHALL NOT be merged if the group already contains a buildpack with the same ID.

The lifecycle:

  • SHALL detect a single group from <order> and write it to <group> using the detection process outlined in the Buildpack Interface Specification
  • SHALL write the resolved build plan from the detected group to <plan>
  • SHALL provide run-image.target data in <analyzed> to buildpacks according to the process outlined in the Buildpack Interface Specification.
  • When CNB_EXEC_ENV is set to a value other than the default:
    • The lifecycle SHALL skip buildpacks that do not support the current execution environment during detection
    • If all buildpacks in a group are skipped due to execution environment mismatch, the lifecycle SHALL continue to the next group in the order
    • This allows the platform to select buildpack groups appropriate for the target execution environment

When image extensions are present in the order (optional), the lifecycle:

  • SHALL execute all image extensions in the order defined in <group> according to the process outlined in the Buildpack Interface Specification.
  • SHALL filter the build plan with dependencies provided by image extensions.
  • SHALL replace run-image in <analyzed> with the selected run image. To select the run image, the lifecycle SHALL inspect each run.Dockerfile output by image extensions, in the order defined in <group>:
    • If all run.Dockerfiles declare FROM ${base_image}, the selected run image SHALL be the original run image in <analyzed>, with extend = true
    • Else the selected run image SHALL be the last image referenced in the FROM statement of the last run.Dockerfile not to declare FROM ${base_image}
      • run-image.image SHALL be the name of the selected run image
      • run-image.reference and run-image.target SHALL be cleared (as they may no longer be accurate)
      • All preceding run.Dockerfiles SHALL be copied to <generated> with suffix .ignore
      • If there are no run.Dockerfiles following the Dockerfile with the selected run image:
        • run-image.extend SHALL be false
      • Else
        • run-image.extend SHALL be true
  • SHALL warn if the selected run image is not found in <run>
  • SHALL record build-image in <analyzed>
    • If there are no build.Dockerfiles:
      • build-image.extend SHALL be false
    • Else
      • build-image.extend SHALL be true

restorer

Usage:

/cnb/lifecycle/restorer \
  [-analyzed <analyzed>] \
  [-build-image <build-image>] \
  [-cache-dir <cache-dir>] \
  [-cache-image <cache-image>] \
  [-daemon] \ # sets <daemon>
  [-gid <gid>] \
  [-group <group>] \
  [-insecure-registry <insecure-registry>...] \
  [-layers <layers>] \
  [-log-level <log-level>] \
  [-skip-layers <skip-layers>] \
  [-uid <uid>] \
  [-run <run> ]
Inputs
Input Environment Variable Default Value Description
<analyzed> CNB_ANALYZED_PATH <layers>/analyzed.toml Path to output analysis metadata (see analyzed.toml
<build-image>* CNB_BUILD_IMAGE Reference to the current build image in an OCI registry (if used <kaniko-dir> must be provided)
<cache-dir> CNB_CACHE_DIR Path to a cache directory
<cache-image> CNB_CACHE_IMAGE Reference to a cache image in an OCI registry
<daemon>^ CNB_USE_DAEMON false Read additional target data for run image from docker daemon
<gid> CNB_GROUP_ID Primary GID of the build image User
<group> CNB_GROUP_PATH <layers>/group.toml Path to group definition (see group.toml)
<insecure-registry>... CNB_INSECURE_REGISTRIES When fetching images from this registry, do not use TLS encryption or certificate verification
<kaniko-dir>^ Kaniko directory (must be /kaniko)
<layers> CNB_LAYERS_DIR /layers Path to layers directory
<log-level> CNB_LOG_LEVEL info Log Level
<skip-layers> CNB_SKIP_LAYERS false Do not perform layer restoration
<uid> CNB_USER_ID UID of the build image User
<run>** CNB_RUN_PATH /cnb/run.toml Path to run file (see run.toml)
<exec-env> CNB_EXEC_ENV production Target execution environment. Standard values: "production", "test", "development".

^ Only needed when using image extensions

* Only needed when using image extensions to extend the build image

** Only needed when using image extensions to extend the run image

Outputs
Output Description
[exit status] (see Exit Code table below for values)
/dev/stdout Logs (info)
/dev/stderr Logs (warnings, errors)
<layers>/<buidpack-id>/store.toml Persistent metadata (see data format in Buildpack Interface Specification)
<layers>/<buidpack-id>/<layer>.toml Files containing the layer content metadata of each analyzed layer (see data format in Buildpack Interface Specification)
<layers>/<buidpack-id>/<layer>.sbom.<ext> Files containing the Software Bill of Materials for each analyzed layer (see Buildpack Interface Specification)
<layers>/<buidpack-id>/<layer>/*. Restored layer contents
<kaniko-dir>/cache Kaniko cache contents
Exit Code Result
0 Success
11 Platform API incompatibility error
12 Buildpack API incompatibility error
1-10, 13-19 Generic lifecycle errors
40-49 Restoration-specific lifecycle errors
  • For each buildpack in <group>, if persistent metadata for that buildpack exists in the analysis metadata, lifecycle MUST write a toml representation of the persistent metadata to <layers>/<buildpack-id>/store.toml
  • If <skip-layers> is true the lifecycle MUST NOT perform layer restoration.
  • Else the lifecycle MUST perform layer restoration for any app image layers or cached layers created by any buildpack present in the provided <group>.
  • When <build-image> is provided (optional), the lifecycle:
    • MUST record the digest reference to the provided <build-image> in <analyzed>
    • MUST copy the OCI manifest and config file for <build-image> to <kaniko-dir>/cache
  • The lifecycle:
    • MUST resolve mirrors for the run-image.reference in <analyzed> and resolve it to a digest reference
    • MUST populate run-image.target data in <analyzed> if not present
    • If <analyzed> has run-image.extend = true, the lifecycle:
      • MUST download from the registry and save in OCI layout format the run-image in <analyzed> to <kaniko-dir>/cache
Layer Restoration

The lifecycle MUST use the provided cache-dir or cache-image to retrieve cache contents. The rules for restoration MUST be followed when determining how and when to store cache layers.

When a platform builds an application with a different execution environment than was used in a previous build (different value of CNB_EXEC_ENV), the platform SHOULD NOT restore layers from the previous build's image. The lifecycle MAY ignore layer metadata from previous builds with different execution environments to ensure proper environment-specific behaviors are maintained.

extender (optional)

If using extender, the platform MUST execute extender in either or both of: the build environment, the run environment

Usage:

/cnb/lifecycle/extender \
  [-analyzed <analyzed>] \
  [-app <app>] \
  [-buildpacks <buildpacks>] \
  [-extended <extended>] \
  [-generated <generated>] \
  [-gid <gid>] \
  [-group <group>] \
  [-kaniko-cache-ttl <kaniko-cache-ttl>] \
  [-kind <kind>] \
  [-layers <layers>] \
  [-log-level <log-level>] \
  [-plan <plan>] \
  [-platform <platform>]
  [-uid <uid>] \
Inputs
Input Env Default Value Description
<analyzed> CNB_ANALYZED_PATH <layers>/analyzed.toml Path to analysis metadata (see analyzed.toml
<app> CNB_APP_DIR /workspace Path to application directory
<build-config> CNB_BUILD_CONFIG_DIR /cnb/build-config Path to build config directory
<buildpacks>* CNB_BUILDPACKS_DIR /cnb/buildpacks Path to buildpacks directory (see Buildpacks Directory Layout)
<extended>** CNB_EXTENDED_DIR <layers>/extended Path to output directory for extended run image layers
<generated> CNB_GENERATED_DIR <layers>/generated Path to directory containing generated Dockerfiles
<gid>* CNB_GROUP_ID Primary GID of the build image User
<group> CNB_GROUP_PATH <layers>/group.toml Path to group definition (see group.toml)
<kaniko-cache-ttl> CNB_KANIKO_CACHE_TTL 2 weeks Kaniko cache TTL
<kaniko-dir> Kaniko directory (must be /kaniko)
<kind> CNB_EXTEND_KIND build Type of image to extend (valid values: build, run)
<layers> CNB_LAYERS_DIR /layers Path to layers directory
<log-level> CNB_LOG_LEVEL info Log Level
<plan>* CNB_PLAN_PATH <layers>/plan.toml Path to resolved build plan (see plan.toml)
<platform> CNB_PLATFORM_DIR /platform Path to platform directory
<uid>* CNB_USER_ID UID of the build image User
<exec-env> CNB_EXEC_ENV production Target execution environment. Standard values: "production", "test", "development".

* Only needed when extending the build image

** Only needed when extending the run image

Outputs

When extending the build image:

  • In addition to the outputs enumerated below, outputs produced by extender include those produced by builder - as the lifecycle will run the build phase after extending the build image.
  • Platforms MUST skip the builder and proceed to the exporter.
Output Description
[exit status] (see Exit Code table below for values)
/dev/stdout Logs (info)
/dev/stderr Logs (warnings, errors)
<kaniko-dir>/cache Kaniko cache contents
Exit Code Result
0 Success
11 Platform API incompatibility error
12 Buildpack API incompatibility error
1-10, 13-19 Generic lifecycle errors
100-109 Extension-specific lifecycle errors
  • For each extension in <group> in order, if a Dockerfile exists in <generated>/<buildpack-id>/<kind>.Dockerfile, the lifecycle:
  • The extended image MUST be an extension of:
    • The build-image in <analyzed> when <kind> is build, or
    • The run-image in <analyzed> when <kind> is run
  • When extending the build image, after all build.Dockerfiles are applied, the lifecycle:
    • SHALL proceed with the build phase using the provided <gid> and <uid>
  • When extending the run image, after all run.Dockerfiles are applied, the lifecycle:
    • If any run.Dockerfile set the label io.buildpacks.rebasable to false or left the label unset:
      • SHALL set the label io.buildpacks.rebasable to false on the extended run image
    • If after the final run.Dockerfile the run image user is root,
      • SHALL fail
    • SHALL copy the manifest and config for the extended run image, along with any new layers, to <extended>/run

builder

The platform MUST execute builder in the build environment

Usage:

/cnb/lifecycle/builder \
  [-analyzed <analyzed>] \
  [-app <app>] \
  [-buildpacks <buildpacks>] \
  [-build-config <build-config>] \
  [-group <group>] \
  [-layers <layers>] \
  [-log-level <log-level>] \
  [-plan <plan>] \
  [-platform <platform>]
Inputs
Input Env Default Value Description
<analyzed> CNB_ANALYZED_PATH <layers>/analyzed.toml Path to analysis metadata (see analyzed.toml
<app> CNB_APP_DIR /workspace Path to application directory
<build-config> CNB_BUILD_CONFIG_DIR /cnb/build-config Path to build config directory
<buildpacks> CNB_BUILDPACKS_DIR /cnb/buildpacks Path to buildpacks directory (see Buildpacks Directory Layout)
<exec-env> CNB_EXEC_ENV production Target execution environment. Standard values: "production", "test", "development".
<group> CNB_GROUP_PATH <layers>/group.toml Path to group definition (see group.toml)
<layers> CNB_LAYERS_DIR /layers Path to layers directory
<log-level> CNB_LOG_LEVEL info Log Level
<plan> CNB_PLAN_PATH <layers>/plan.toml Path to resolved build plan (see plan.toml)
<platform> CNB_PLATFORM_DIR /platform Path to platform directory
Outputs
Output Description
[exit status] (see Exit Code table below for values)
/dev/stdout Logs (info)
/dev/stderr Logs (warnings, errors)
<layers>/<buildpack ID>/<layer> Layer contents (see Buildpack Interface Specfication
<layers>/<buildpack ID>/<layer>.toml Layer metadata (see Buildpack Interface Specfication
<layers>/config/metadata.toml Build metadata (see metadata.toml)
Exit Code Result
0 Success
11 Platform API incompatibility error
12 Buildpack API incompatibility error
1-10, 13-19 Generic lifecycle errors
51 Buildpack build error
50, 52-59 Build-specific lifecycle errors
  • The lifecycle SHALL execute all buildpacks in the order defined in <group> according to the process outlined in the Buildpack Interface Specification.
  • SHALL provide run-image.target data in <analyzed> to buildpacks according to the process outlined in the Buildpack Interface Specification.
  • The lifecycle SHALL add all invoked buildpacks to<layers>/config/metadata.toml.
  • The lifecycle SHALL aggregate all processes and slices returned by buildpacks in <layers>/config/metadata.toml.
  • The lifecycle SHALL record the buildpack-provided default process type in <layers>/config/metadata.toml.
    • The lifecycle SHALL treat web processes defined by buildpacks implementing Buildpack API < 0.6 as default = true.

exporter

Usage:

/cnb/lifecycle/exporter \
  [-analyzed <analyzed>] \
  [-app <app>] \
  [-cache-dir <cache-dir>] \
  [-cache-image <cache-image>] \
  [-daemon] \ # sets <daemon>
  [-extended <extended>] \
  [-gid <gid>] \
  [-group <group>] \
  [-insecure-registry <insecure-registry>...] \
  [-launch-cache <launch-cache> ] \
  [-launcher <launcher> ] \
  [-launcher-sbom <launcher-sbom> ] \
  [-layers <layers>] \
  [-layout] \ # sets <layout>
  [-layout-dir] \ # sets <layout-dir>
  [-log-level <log-level>] \
  [-parallel] \
  [-process-type <process-type> ] \
  [-project-metadata <project-metadata> ] \
  [-report <report> ] \
  [-run <run>] \
  [-uid <uid> ] \
  <image> [<image>...]
Inputs
Input Environment Variable Default Value Description
<analyzed> CNB_ANALYZED_PATH <layers>/analyzed.toml Path to analysis metadata (see analyzed.toml
<app> CNB_APP_DIR /workspace Path to application directory
<cache-dir> CNB_CACHE_DIR Path to a cache directory
<cache-image> CNB_CACHE_IMAGE Reference to a cache image in an OCI registry
<daemon> CNB_USE_DAEMON false Export image to docker daemon
<extended>** CNB_EXTENDED_DIR <layers>/extended Path to directory containing extended run image layers
<gid> CNB_GROUP_ID Primary GID of the build image User
<group> CNB_GROUP_PATH <layers>/group.toml Path to group file (see group.toml)
<image> Tag reference to which the app image will be written
<insecure-registry>... CNB_INSECURE_REGISTRIES When fetching images from this registry, do not use TLS encryption or certificate verification
<launch-cache> CNB_LAUNCH_CACHE_DIR Path to a cache directory containing launch layers
<launcher-sbom> /cnb/lifecycle Path to directory containing SBOM files describing the launcher executable
<launcher> /cnb/lifecycle/launcher Path to the launcher executable
<layers>/config/metadata.toml Build metadata (see metadata.toml
<layers> CNB_LAYERS_DIR /layers Path to layer directory
<layout> CNB_USE_LAYOUT false (experimental) Export image to disk in OCI layout format
<layout-dir> CNB_LAYOUT_DIR (experimental) Path to a root directory where the images are saved in OCI layout format
<log-level> CNB_LOG_LEVEL info Log Level
<parallel> CNB_PARALLEL_EXPORT false Export app image and cache in parallel
<process-type> CNB_PROCESS_TYPE Default process type to set in the exported image
<project-metadata> CNB_PROJECT_METADATA_PATH <layers>/project-metadata.toml Path to a project metadata file (see project-metadata.toml
<report> CNB_REPORT_PATH <layers>/report.toml Path to report (see report.toml
<run> CNB_RUN_PATH /cnb/run.toml Path to run file (see run.toml
<uid> CNB_USER_ID UID of the build image User
SOURCE_DATE_EPOCH Timestamp for created time in app image config

** Only needed when extending the run image

  • At least one <image> must be provided
  • Each <image> MUST be a valid tag reference
  • If <daemon> is false and more than one <image> is provided they MUST refer to the same registry
  • The <run-image> will be read from analyzed.toml
Outputs
Output Description
[exit status] Success (0), or error (1+)
/dev/stdout Logs (info)
/dev/stderr Logs (warnings, errors)
<image> Exported app image (see Buildpack Interface Specfication
Exit Code Result
0 Success
11 Platform API incompatibility error
12 Buildpack API incompatibility error
1-10, 13-19 Generic lifecycle errors
60-69 Export-specific lifecycle errors

  • The lifecycle SHALL write the same app image to each <image> tag

  • The app image:

    • If image extensions were used to extend the run-image in analyzed.toml:
      • MUST be based on the image in <extended>/run
    • Else:
    • All base image layers and any extension layers SHALL be preserved
    • All base image config values SHALL be preserved unless this conflicts with another requirement
    • MUST contain all buildpack-provided launch layers as determined by the Buildpack Interface Specfication
    • MUST contain a layer containing all Software Bill of Materials (SBOM) files for launch as determined by the Buildpack Interface Specfication if they are present
      • <layers>/sbom/launch/<buildpack-id>/sbom.<ext> MUST contain the buildpack-provided launch SBOM
      • <layers>/sbom/launch/<buildpack-id>/<layer-id>/sbom.<ext> MUST contain the buildpack-provided layer SBOM if <layer-id> is a launch layer
      • <layers>/sbom/launch/sbom.legacy.json MAY contain the legacy buildpack-provided non-standard Bill of Materials for launch (where supported)
      • <layers>/sbom/launch/buildpacksio_lifecycle/launcher/sbom.<ext> MUST contain the CNB-provided launcher SBOM if present in the /cnb/lifecycle directory
    • MUST contain one or more app layers as determined by the Buildpack Interface Specfication
    • MUST contain one or more launcher layers that include:
      • A file with the contents of the <launcher> file at path /cnb/lifecycle/launcher
      • One symlink per buildpack-provided process type with name /cnb/process/<type> and target /cnb/lifecycle/launcher
    • MUST contain a layer that includes <layers>/config/metadata.toml
    • If <process-type> matches a buildpack-provided process:
      • MUST have ENTRYPOINT=/cnb/process/<process-type>
    • Else if <process-type> is provided and does not match a buildpack-provided process:
      • MUST fail
    • Else if there is a buildpack-provided default process type in <layers>/config/metadata.toml:
      • MUST have ENTRYPOINT=/cnb/process/<buildpack-default-process-type>
    • Else:
      • MUST have ENTRYPOINT set to /cnb/lifecycle/launcher
    • MUST contain the following Env entries
      • CNB_LAYERS_DIR=<layers>
      • CNB_APP_DIR=<app>
      • PATH=/cnb/process:$PATH where $PATH is the value of $PATH on the run-image.
    • MUST have the working directory set to the value of <app>.
    • MUST contain the following labels
      • io.buildpacks.lifecycle.metadata: see lifecycle metadata label
      • io.buildpacks.project.metadata: the value of which SHALL be the json representation of <project-metadata>
      • io.buildpacks.build.metadata: see build metadata
      • If image extensions were used to extend the run image and <extended>/run/<image config> has the label io.buildpacks.rebasable set to true:
        • io.buildpacks.rebasable SHALL be true
      • Else
        • io.buildpacks.rebasable SHALL be false

  • To ensure build reproducibility, the lifecycle:

    • SHOULD set the modification time of all files in newly created layers to a constant value
    • SHOULD set the created time in image config to SOURCE_DATE_EPOCH, or to a constant value if not defined

  • The lifecycle SHALL write a report to <report> describing the exported app image

  • The <layers> directory:

    • MUST include all Software Bill of Materials (SBOM) files for build as determined by the Buildpack Interface Specfication if they are present
      • <layers>/sbom/build/<buildpack-id>/sbom.<ext> MUST contain the buildpack-provided build SBOM
      • <layers>/sbom/build/<buildpack-id>/<layer-id>/sbom.<ext> MUST contain the buildpack-provided layer SBOM if <layer-id> is not a launch layer.
      • <layers>/sbom/build/sbom.legacy.json MAY contain the legacy buildpack-provided non-standard Bill of Materials for build (where supported)
      • <layers>/sbom/build/buildpacksio_lifecycle/sbom.<ext> MUST contain the CNB-provided lifecycle SBOM if present in the /cnb/lifecycle directory

  • If a cache is provided the lifecycle:

    • SHALL write the contents of all cached layers and any provided layer-associated SBOM files to the cache
    • SHALL record the diffID and layer content metadata of all cached layers in the cache

  • If <layout> is true the lifecycle:

    • SHALL write the app image on disk following the rules to convert the reference to a path

creator

The platform MUST execute creator in the build environment

Usage:

/cnb/lifecycle/creator \
  [-app <app>] \
  [-buildpacks <buildpacks>] \
  [-cache-dir <cache-dir>] \
  [-cache-image <cache-image>] \
  [-daemon] \ # sets <daemon>
  [-gid <gid>] \
  [-insecure-registry <insecure-registry>...] \
  [-launch-cache <launch-cache> ] \
  [-launcher <launcher> ] \
  [-layers <layers>] \
  [-layout] \ # sets <layout>
  [-layout-dir] \ # sets <layout-dir>
  [-log-level <log-level>] \
  [-order <order>] \
  [-platform <platform>] \
  [-previous-image <previous-image> ] \
  [-process-type <process-type> ] \
  [-project-metadata <project-metadata> ] \
  [-report <report> ] \
  [-run <run>] \
  [-run-image <run-image>] \
  [-skip-restore <skip-restore>] \
  [-tag <tag>...] \
  [-uid <uid> ] \
   <image>
Inputs

Running creator SHALL be equivalent to running detector, analyzer, restorer, builder and exporter in order with identical inputs where they are accepted, with the following exceptions.

Input Environment Variable Default Value Description
<previous-image> CNB_PREVIOUS_IMAGE <image> Image reference to be analyzed (usually the result of the previous build)
<skip-restore> CNB_SKIP_RESTORE false Prevent buildpacks from reusing layers from previous builds, by skipping the restoration of any data to each buildpack's layers directory, with the exception of store.toml.
<tag>... Additional tag to apply to exported image
  • If <skip-restore> is true the creator SHALL skip the restoration of any data to each buildpack's layers directory, with the exception of store.toml.
  • If the platform provides one or more <tag> inputs they SHALL be treated as additional <image> inputs to the exporter
Outputs

Outputs produced by creator are identical to those produced by exporter, with the following additional expanded set of error codes.

Exit Code Result
0 Success
11 Platform API incompatibility error
12 Buildpack API incompatibility error
1-10, 13-19 Generic lifecycle errors
20-29 Detection-specific lifecycle errors
30-39 Analysis-specific lifecycle errors
40-49 Restoration-specific lifecycle errors
50-59 Build-specific lifecycle errors
60-69 Export-specific lifecycle errors

rebaser

Usage:

/cnb/lifecycle/rebaser \
  [-daemon] \ # sets <daemon>
  [-force] \
  [-gid <gid>] \
  [-insecure-registry <insecure-registry>...] \
  [-log-level <log-level>] \
  [-previous-image <previous-image>] \
  [-report <report> ] \
  [-run-image <run-image> | -image <run-image> ] \ # -image is Deprecated
  [-uid <uid>] \
  <image> [<image>...]
Inputs
Input Environment Variable Default Value Description
<daemon> CNB_USE_DAEMON false Export image to docker daemon
<force> CNB_FORCE_REBASE false Allow unsafe rebase
<gid> CNB_GROUP_ID Primary GID of the build image User
<image> App image to rebase
<insecure-registry>... CNB_INSECURE_REGISTRIES When fetching images from this registry, do not use TLS encryption or certificate verification
<log-level> CNB_LOG_LEVEL info Log Level
<previous-image> derived from <image> Previous image reference
<report> CNB_REPORT_PATH <layers>/report.toml Path to report (see report.toml
<run-image> CNB_RUN_IMAGE derived from <image> Run image reference
<uid> CNB_USER_ID UID of the build image User
  • At least one <image> must be provided
  • If <image> has the label io.buildpacks.rebasable set to false, the lifecycle SHALL fail unless <force> is true
  • Each <image> MUST be a valid tag reference
  • If <daemon> is false and more than one <image> is provided, the images MUST refer to the same registry.
  • If <previous-image> is provided by the platform, the value will be used as the app image to rebase. <previous-image> must NOT be modified unless specified again in <image>.
  • Else <previous-image> value will be derived from the first <image>.
  • If <run-image> is not provided by the platform, the value will be resolved from the contents of the runImage key in the io.buildpacks.lifecycle.metdata label on <image>, or stack.runImage if not found (for compatibility with older platforms; see deprecations).
Outputs
Output Description
[exit status] (see Exit Code table below for values)
/dev/stdout Logs (info)
/dev/stderr Logs (warnings, errors)
<image> Rebased app image (see Buildpack Interface Specfication)
Exit Code Result
0 Success
11 Platform API incompatibility error
12 Buildpack API incompatibility error
1-10, 13-19 Generic lifecycle errors
70-79 Rebase-specific lifecycle errors
  • The lifecycle SHALL write the same app image to each <image> tag
  • The rebased app image SHALL be identical to <image>, with the following modifications:
    • Run image layers SHALL be defined as Layers in <image> up to and including the layer with diff ID matching the value of run-image.top-layer from the io.buildpacks.lifecycle.metadata label
    • Run image layers SHALL be replaced with the layers from the new <run-image>
    • The value of io.buildpacks.lifecycle.metadata SHALL be modified as follows
      • run-image.reference SHALL uniquely identify <run-image>
      • run-image.top-layer SHALL be set to the uncompressed digest of the top layer in <run-image>
    • The value of io.buildpacks.base.* labels and io.buildpacks.stack.* labels (if present) SHALL be modified to that of the new run-image
  • If <force> is true, the following target data values in the output <image> config MUST be derived from the new <run-image>:
    • os
    • architecture
    • variant (if specified)
    • io.buildpacks.base.distro.name (if specified)
    • io.buildpacks.base.distro.version (if specified)
  • Else the target data above MUST match the old run image if <force> is false
  • If <force> is true and the provided <run-image> is not found in runImage.image or runImage.mirrors:
    • run-image.image SHALL be the provided <run-image>
    • run-image.mirrors SHALL be omitted
  • Else if <force> is false, the provided <run-image> MUST be found in runImage.image or runImage.mirrors
  • To ensure build reproducibility, the lifecycle:
    • SHOULD set the created time in image config to a constant
  • The lifecycle SHALL write a report to <report> describing the rebased app image

launcher

Usage:

/cnb/process/<process-type> [<arg>...]
# OR
/cnb/lifecycle/launcher [--] [<cmd> <arg>...]
Inputs
Input Environment Variable Default Value Description
<app> CNB_APP_DIR /workspace Path to application directory
<exec-env> CNB_EXEC_ENV production Target execution environment. Standard values: "production", "test", "development".
<layers> CNB_LAYERS_DIR /layers Path to layer directory
<process-type> type of process to launch
<direct> Process execution strategy
<cmd> Command to execute
<args> Arguments to command
<layers>/config/metadata.toml Build metadata (see metadata.toml
<layers>/<buildpack-id>/<layer>/ Launch Layers

A command (<cmd>), arguments to that command (<args>), a working directory (<working-dir>), and an execution strategy (<direct>) comprise a process definition. Processes MAY be buildpack-defined or user-defined.

The launcher:

  • MUST derive the values of <cmd>, <args>, <working-dir>, and <direct> as follows:
  • If the final path element in $0, matches the type of any buildpack-provided process type
    • <process-type> SHALL be the final path element in $0
    • The lifecycle:
      • MUST select the process with type equal to <process-type> from <layers>/config/metadata.toml that is eligible for the current execution environment
      • If no process with the requested type is eligible for the current execution environment, the lifecycle MUST fail
      • A process is considered eligible for the current execution environment if:
        • It has no execution environment specified in exec-env, OR
        • Its exec-env includes the value of <exec-env>, OR
        • Its exec-env includes the special value "*" which indicates compatibility with all execution environments
      • MUST set <working-dir> to the value defined for the process in <layers>/config/metadata.toml, or to <app> if not defined
      • If the buildpack that provided the process supports default process args
        • <direct> SHALL be true
        • MUST replace any buildpack provided default <args> with any user-provided <args>
      • Else
        • <direct> value defined by buildpack SHALL be honored
        • MUST append any user-provided <args> to process arguments
  • Else
    • If $1 is --
      • <direct> SHALL be true
      • <cmd> SHALL be $2
      • <args> SHALL be ${@3:}
      • <working-dir> SHALL be <app>
    • Else
      • <direct> SHALL be false
      • <cmd> SHALL be $1
      • <args> SHALL be ${@2:}
      • <working-dir SHALL be <app>
Execution

Given the start command and execution strategy,

  1. The launcher MUST set all buildpack-provided launch environment variables as described in the Environment section.

  2. The launcher MUST

    1. execute each file in each <layers>/<layer>/exec.d directory in the launch environment, with working directory <app>, and set the returned variables in the launch environment before continuing,
      1. Firstly, in order of /bin/build execution used to construct the OCI image.
      2. Secondly, in alphabetically ascending order by layer directory name.
      3. Thirdly, in alphabetically ascending order by file name.
    2. execute each file in each <layers>/<layer>/exec.d/<process> directory in the launch environment, with working directory <app>, and set the returned variables in the launch environment before continuing,
      1. Firstly, in order of /bin/build execution used to construct the OCI image.
      2. Secondly, in alphabetically ascending order by layer directory name.
      3. Thirdly, in alphabetically ascending order by file name.

  3. If using an execution strategy involving a shell, the launcher MUST use a single shell process, with working directory <app>, to

    1. source each file in each <layers>/<layer>/profile.d directory,
      1. Firstly, in order of /bin/build execution used to construct the OCI image.
      2. Secondly, in alphabetically ascending order by layer directory name.
      3. Thirdly, in alphabetically ascending order by file name.
    2. source each file in each <layers>/<layer>/profile.d/<process> directory,
      1. Firstly, in order of /bin/build execution used to construct the OCI image.
      2. Secondly, in alphabetically ascending order by layer directory name.
      3. Thirdly, in alphabetically ascending order by file name.
    3. source †<app>/.profile or ‡<app>/.profile.bat if it is present.

  4. The launcher MUST set the working directory for the start command to <working-dir>, or to <app> if <working-dir> is not specified.

  5. The launcher MUST invoke the start command with the decided execution strategy.

†When executing a process using any execution strategy, the launcher SHOULD replace the launcher process in memory without forking it.

†When executing a process with Bash, the launcher SHOULD additionally replace the Bash process in memory without forking it.

‡When executing a process with Command Prompt, the launcher SHOULD start a new process with the same security context, terminal, working directory, STDIN/STDOUT/STDERR handles and environment variables as the Command Prompt process.

Outputs

If the launcher errors before executing the process it will have one of the following error codes:

Exit Code Result
11 Platform API incompatibility error
12 Buildpack API incompatibility error
80-89 Launch-specific lifecycle errors

Otherwise, the exit code shall be the exit code of the launched process.

The launcher:

Run Image Resolution

Given run metadata shall be resolved as follows:

  • By choosing the <run-image> for a given <app-image>:
    • If any of image.image or image.mirrors has a registry matching that of <app-image> and is accessible with read permissions:
      • This value will become the <run-image>
    • If none of image.image or image.mirrors has a registry matching that of <app-image>:
      • The first value of image.image or image.mirrors that is accessible with read permissions will become the <run-image>
  • By choosing mirrors information for a given <run-image>:
    • The first image in [[images]] where image.image or one of image.mirrors matches <run-image>
    • Else the first image in [[images]]

Registry Authentication

The platform MAY set CNB_REGISTRY_AUTH in the lifecycle execution environment, where value of CNB_REGISTRY_AUTH MUST be valid JSON object and MAY contain any number of <regsitry> to <auth-header> mappings. If CNB_REGISTRY_AUTH is set and <registry> matches the registry of an image reference, the lifecycle SHOULD set the value of the Authorization HTTP header to <auth-header> when attempting to read or write the image located at the given reference.

If CNB_REGISTRY_AUTH is unset and a docker config.json file is present, the lifecycle SHOULD use the contents of this file to authenticate with any matching registry. The lifecycle SHOULD adhere to established docker conventions when checking for the existence of or interpreting the contents of a config.json file.

The lifecycle MAY provide other mechanisms by which a platform can supply registry credentials.

The lifecycle MUST attempt to authenticate anonymously if no matching credentials are found.

Experimental Features

Where noted, certain features are considered experimental and susceptible to change in a future API version.

The platform SHOULD set CNB_EXPERIMENTAL_MODE=<warn|error|silent> in the lifecycle's execution environment to control the behavior of experimental features.

When an experimental feature is invoked, the lifecycle:

  • SHALL fail if CNB_EXPERIMENTAL_MODE is unset
  • SHALL warn and continue if CNB_EXPERIMENTAL_MODE=warn
  • SHALL fail if CNB_EXPERIMENTAL_MODE=error
  • SHALL continue without warning if CNB_EXPERIMENTAL_MODE=silent

Buildpacks

Buildpacks Directory Layout

The buildpacks directory MUST contain unarchived buildpacks such that:

  • Each top-level directory is a buildpack ID.
  • Each second-level directory is a buildpack version.

Image Extensions

Image Extensions Directory Layout

The image extensions directory MUST contain unarchived image extensions such that:

  • Each top-level directory is an image extension ID.
  • Each second-level directory is an image extension version.

Security Considerations

The platform SHOULD run each phase of the lifecycle in an isolated container to prevent untrusted app and buildpack code from accessing storage credentials needed during the export and analysis phases. A more thorough explanation is provided in the Buildpack Interface Specification.

Additional Guidance

Environment

Buildpack Environment

Base Image-Provided Variables

The following variables SHOULD be set in the lifecycle execution environment and SHALL be directly inherited by the buildpack without modification:

Env Variable Description
HOME Current user's home directory
POSIX Path Variables

The following variables SHOULD be set in the lifecycle execution environment and MAY be modified by prior buildpacks before they are provided to a given buildpack:

Env Variable Layer Path Contents
PATH /bin binaries
LD_LIBRARY_PATH /lib shared libraries
LIBRARY_PATH /lib static libraries
CPATH /include header files
PKG_CONFIG_PATH /pkgconfig pc files

The platform SHOULD NOT assume any other base-image-provided environment variables are inherited by the buildpack.

User-Provided Variables

User-provided environment variables MUST be supplied by the platform as files in the <platform>/env/ directory.

Each file SHALL define a single environment variable, where the file name defines the key and the file contents define the value.

User-provided environment variables that are POSIX path variables MAY be modified by prior buildpacks before they are provided to a given buildpack, however the user-provided value is always prepended to the buildpack-provided value.

User-provided environment variables that are not POSIX path variables MAY NOT be modified by prior buildpacks before they are provided to a given buildpack.

The platform SHOULD NOT set user-provided environment variables directly in the lifecycle execution environment.

Operator-Defined Variables

Operator-provided environment variables MUST be supplied by the platform as files in the <build-config>/env/ directory.

Each file SHALL define a single environment variable, where the file name defines the key and the file contents define the value.

The <build-config>/env/ directory follows the Environment Variable Modification Rules outlined in the Buildpack Interface Specification, except for the modification behavior when no period-delimited suffix is provided; when no suffix is provided, the behavior is default.

Operator-defined environment variables MAY be modified by prior buildpacks before they are provided to a given buildpack, however the operator-defined value is always applied after the buildpack-provided value.

The platform SHOULD NOT set operator-provided environment variables directly in the lifecycle execution environment.

Launch Environment

User-provided modifications to the process execution environment SHOULD be set directly in the lifecycle execution environment.

The process SHALL inherit both base-image-provided and user-provided variables from the lifecycle execution environment with the following exceptions:

  • CNB_APP_DIR, CNB_LAYERS_DIR and CNB_PROCESS_TYPE SHALL NOT be set in the process execution environment.
  • /cnb/process SHALL be removed from the beginning of PATH.
  • The lifecycle SHALL apply buildpack-provided modifications to the environment as outlined in the Buildpack Interface Specification.

Caching

If caching is enabled the platform is responsible for providing the lifecycle with access to the correct cache. Whenever possible, the platform SHOULD provide the same cache to each rebuild of a given app image. Cache locality and availability MAY vary between platforms.

Build Reproducibility

When given identical inputs all build and rebase operations:

  • SHOULD produce app images with identical imageIDs
  • If exporting directly to a registry
    • SHOULD produce app images with identical manifest digests
  • MAY output other non-reproducible artifacts

To achieve reproducibility the lifecycle SHOULD set the following to a constant, rather than an accurate value:

  • file modification times in generated layers
  • image creation time

Because compressions algorithms and manifest whitespace affect the image digest, an app image exported to the docker daemon and subsequently pushed to a registry MAY have a different digest than an app image exported directly to a registry by the lifecycle, even when all other inputs are held constant.

If buildpacks do not generate layer contents or layer metadata reproducibly, builds MAY NOT be reproducibile even when identical source code and buildpacks are provided to the lifecycle.

All app image labels SHOULD contain only reproducible values.

For more information on build reproducibility see https://reproducible-builds.org/

Map an image reference to a path in the layout directory

An image reference refers to either a tag reference or a digest reference:

  • A tag reference refers to an identifier of form <registry>/<repo>/<image>:<tag>
  • A digest reference refers to a content addressable identifier of form <registry>/<repo>/<image>@<algorithm>:<digest>

The image reference will be mapped to a path in the layout directory following these rules:

  • If the image points to a tag reference:
    • The path MUST be <layout-dir>/<registry>/<repo>/<image>/<tag>
  • Else if the image points to a digest reference:
    • The path MUST be <layout-dir>/<registry>/<repo>/<image>/<algorithm>/<digest>

Data Format

Files

analyzed.toml (TOML)

[image]
  reference = "<image reference>"

[metadata]
# layer metadata

[run-image]
  image = "<image>"
  reference = "<image reference>"
  extend = false
  [target]
  os = "<OS name>"
  arch = "<architecture>"
  variant = "<architecture variant>"
  [target.distro]
  name = "<OS distribution name>"
  version = "<OS distribution version>"

[build-image]
  reference = "<image reference>"

Where:

  • previous-image.reference MUST be either:
    • A digest reference to an image in an OCI registry
    • The ID of an image in a docker daemon
    • The path to an image in OCI layout format
  • previous-image.metadata MUST be the TOML representation of the layer metadata label
  • run-image.reference MUST be either:
    • A digest reference to an image in an OCI registry
    • The ID of an image in a docker daemon
    • The path to an image in OCI layout format
  • run-image.image MUST be the platform- or extension-provided image name
  • run-image.target contains the target data for the image
    • If target distribution data is missing, it will be inferred from /etc/os-release for Linux images; furthermore, if the image contains the label io.buildpacks.stack.id with value io.buildpacks.stacks.bionic, the lifecycle SHALL assume the following values:
      • run-image.target.os = "linux"
      • run-image.target.arch = "arm64"
      • run-image.target.distro.name = "ubuntu"
      • run-image.target.distro.version = "18.04"

group.toml (TOML)

[[group]]
id = "<buildpack ID>"
version = "<buildpack version>"
api = "<buildpack API version>"
homepage = "<buildpack homepage>"

[[group-extensions]]
id = "<image extension ID>"
version = "<image extension version>"
api = "<image extension API version>"
homepage = "<image extension homepage>"

Where:

  • id, version, and api MUST be present for each buildpack object in a group.

metadata.toml (TOML)

buildpack-default-process-type = "<process type>"

[[buildpacks]]
id = "<buildpack ID>"
version = "<buildpack version>"
api = "<buildpack API version>"
optional = false

[[extensions]]
id = "<image extension ID>"
version = "<image extension version>"
api = "<image extension API version>"

[[processes]]
type = "<process type>"
command = ["<command>"]
args = ["<arguments>"]
direct = false
working-dir = "<working directory>"
exec-env = ["<execution environment>"] # Optional. If not specified, applies to all execution environments. The special value "*" indicates compatibility with all execution environments. If exec-env is ["*"] or not specified, the process is eligible for all execution environments.

[[slices]]
paths = ["<app sub-path glob>"]

Where:

  • id, version, and api MUST be present for each buildpack
  • processes contains the complete set of processes contributed by all buildpacks
    • The exec-env field MUST be set to ["*"] if the process applies to all execution environments
    • The exec-env field MUST contain specific execution environment values (e.g., ["production"], ["test", "development"]) if the process is restricted to certain environments
    • If exec-env is not specified, it SHALL be treated as ["*"] (applies to all environments)
  • slices contains the complete set of slices defined by all buildpacks

order.toml (TOML)

[[order]]
[[order.group]]
id = "<buildpack ID>"
version = "<buildpack version>"
optional = false

[[order-extensions]]
[[order-extensions.group]]
id = "<image extension ID>"
version = "<image extension version>"

Where:

  • Both id and version MUST be present for each buildpack object in a group.
  • The value of optional MUST default to false if not specified.

plan.toml (TOML)

[[entries]]

  [[entries.providers]]
    id = "<buildpack or image extension ID>"
    version = "<buildpack or image extension version>"
    extension = false

  [[entries.requires]]
    name = "<dependency name>"
    [entries.requires.metadata]
      # arbitrary data describing the required dependency

Where:

  • entries MAY be empty
  • Each entry:
    • MUST contain at least one buildpack or image extension in providers
      • If the provider is an image extension (optional), extension MUST be true; the value of extension MUST default to false if not specified
    • MUST contain at least one dependency requirement in requires
    • MUST exclusively contain dependency requirements with the same <dependency name>

project-metadata.toml (TOML)

[source]
type = "<source type>"

[source.version]
# arbitrary data

[source.metadata]
# arbitrary data

Where:

  • All values are optional
  • type, if present, SHOULD contain the type of location where the provided app source is stored (e.g git, s3)
  • version, if present, SHOULD contain data uniquely identifying the particular version of the provided source
  • metadata MAY contain additional arbitrary data about the provided source

report.toml (TOML)

[image]
tags = ["<tag reference>"]
digest = "<image digest>"
image-id = "<imageID>"
manifest-size = "<manifest size in bytes>"

Where:

  • tags MUST contain all tag references to the exported app image
  • If the app image was exported to an OCI registry
    • digest MUST contain the image digest
    • manifest-size MUST contain the manifest size in bytes
  • If the app image was exported to a docker daemon
    • imageID MUST contain the imageID

run.toml (TOML)

[[images]]
 image = "<image>"
 mirrors = ["<mirror1>", "<mirror2>"]

Where:

  • image.image MAY be a tag reference to a run image in an OCI registry
  • image.mirrors MUST NOT be present if image.image is not present
  • image.mirrors MAY contain one or more tag references to run images in OCI registries
  • All image.mirrors:
    • SHOULD reference an image with ID identical to that of image.image
  • image.image and image.mirrors.[] SHOULD each refer to a unique registry

system.toml (TOML)

[[system.pre.buildpacks]]
  id = "<buildpack ID>"
  version = "<buildpack version>"
  optional = false

[[system.post.buildpacks]]
  id = "<buildpack ID>"
  version = "<buildpack version>"
  optional = false

Where:

  • system.pre.buildpacks MAY contain a list of buildpacks to insert at the beginning of every order group before detection.
  • system.post.buildpacks MAY contain a list of buildpacks to insert at the end of every order group before detection.
  • Both id and version MUST be present for each buildpack object in system.pre.buildpacks and system.post.buildpacks.
  • The value of optional MUST default to false if not specified.

Labels

io.buildpacks.build.metadata (JSON)

{
  "processes": [
    {
      "type": "<process-type>",
      "command": ["<command>"],
      "args": [
        "<args>"
      ],
      "direct": false,
      "working-dir": "<working-dir>",
      "buildpackID": "<buildpack ID>",
      "exec-env": ["<execution environment>"] // Array of execution environments. Use ["*"] for all environments. If omitted, defaults to ["*"]
    }
  ],
  "buildpacks": [
    {
      "id": "<buildpack ID>",
      "version": "<buildpack version>",
      "homepage": "<buildpack homepage>",
      "api": "<buildpack API version>"
    }
  ],
  "extensions": [
    {
      "id": "<extension ID>",
      "version": "<extension version>",
      "homepage": "<extension homepage>",
      "api": "<buildpack API version>"
    }
  ],
 "launcher": {
    "version": "<launcher-version>",
    "source": {
      "git": {
        "repository": "<launcher-source-repository>",
        "commit": "<launcher-source-commit>"
      }
    }
  }
}

Where:

  • processes MUST contain all buildpack contributed processes
  • buildpacks MUST contain the detected group
  • launcher.version SHOULD contain the version of the launcher binary included in the app
  • launcher.source.git.repository SHOULD contain the git repository containing the launcher source code
  • launcher.source.git.commit SHOULD contain the git commit from which the given launcher was built

io.buildpacks.lifecycle.metadata (JSON)

{
  "app": [
    {"sha": "<slice-layer-diffID>"}
  ],
  "sbom": {
    "sha": "<BOM-layer-diffID>"
  },
  "config": {
    "sha": "<config-layer-diffID>"
  },
  "exec-env": "<execution environment>",
  "launcher": {
    "sha": "<launcher-layer-diffID>"
  },
  "buildpacks": [
    {
      "key": "<buildpack-id>",
      "version": "<buildpack-version>",
      "layers": {
        "<layer-name>": {
          "sha": "<layer-diffID>",
          "data": {},
          "build": false,
          "launch": false,
          "cache": false
        }
      }
    }
  ],
  "runImage": {
    "image": "cnbs/sample-stack-run:bionic",
    "mirrors": = ["<mirror1>", "<mirror2>"],
    "topLayer": "<run-image-top-layer-diffID>",
    "reference": "<run-image-reference>"
  }
}

Where:

  • app MUST contain one entry per app slice layer where
    • sha MUST contain the digest of the uncompressed layer
  • sbom.sha MUST contain the digest of the uncompressed layer containing buildpack-provided Software Bill of Materials
  • config.sha MUST contain the digest of the uncompressed layer containing launcher config
  • launcher.sha MUST contain the digest of the uncompressed layer containing the launcher binary
  • buildpacks MUST contain one entry per buildpack that participated in the build where
    • key is required and MUST contain the buildpack ID
    • version is required and MUST contain the buidpack Version
    • layers is required and MUST contain one entry per launch layer contributed by the given buildpack.
    • For each entry in layers:
      • The key MUST be the name of the layer
      • The value MUST contain JSON representation of the layer.toml with an additional sha key, containing the digest of the uncompressed layer
      • The value MUST contain an additional sha key, containing the digest of the uncompressed layer
  • runImage.image and runImage.mirrors MUST be resolved from run.toml from the given <run-image>
  • runImage.topLayer MUST contain the uncompressed digest of the top layer of the run-image
  • runImage.reference MUST uniquely identify the run image. It MAY contain one of the following
    • An image ID (the digest of the uncompressed config blob)
    • A digest reference to a manifest stored in an OCI registry

io.buildpacks.project.metadata (JSON)

{
  "source": {
    "type": "<type>",
    "version": {
     // arbitrary version data
    },
    "metadata": {
    // arbitrary data
    }
  }
}

This label MUST contain the JSON representation of project-metadata.toml

Deprecations

This section describes all the features that are deprecated.

io.buildpacks.stack.* Labels

Deprecated in Platform API 0.12.

For compatibility with older platforms and older buildpacks, base image authors SHOULD ensure for build images and run images:

  • The image config's Label field has the label io.buildpacks.stack.id set to the stack ID.
  • The image config's Label field has the label io.buildpacks.stack.mixins set to a JSON array containing mixin names for each mixin applied to the image.

And for build images:

  • The image config's Env field has the environment variable CNB_STACK_ID set to the stack ID.

Where CNB_STACK_ID SHALL be directly inherited by buildpacks without modification.

To upgrade, the platform SHOULD upgrade all buildpacks to use Buildpack API 0.10 or greater.

io.buildpacks.lifecycle.metadata (JSON) stack Key

Deprecated in Platform API 0.12.

The stack key is deprecated.

  "stack": {
    "runImage": {
      "image": "cnbs/sample-stack-run:bionic",
      "mirrors": ["<mirror1>", "<mirror2>"]
    }
  }

Where stack MUST contain the same data as the top-level runImage key.

To upgrade, the platform SHOULD read the top-level runImage key instead.