source-to-image (sti)

Source-to-image (sti) is a tool for building reproducible docker images. sti produces ready-to-run images by injecting source code into a docker image and assembling a new docker image which incorporates the builder image and built source, and is ready to use with docker run. sti supports incremental builds which re-use previously downloaded dependencies, previously built artifacts, etc.

Interested in learning more? Read on!

Want to just get started now? Check out the instructions.

Philosophy

1. Simplify the process of application source + builder image -> usable image for most use cases (the 80%)
2. Define and implement a workflow for incremental build that eventually uses only docker primitives
3. Develop tooling that can assist in verifying that two different builder images result in the same "docker run" outcome for the same input
4. Use native docker primitives to accomplish this - map out useful improvements to docker that benefit all image builders

Anatomy of a builder image

Creating builder images is easy. sti expects you to supply the following scripts to use with an image:

1. assemble - builds and/or deploys the source
2. run- runs the assembled artifacts
3. save-artifacts (optional) - captures the artifacts from a previous build into the next incremental build
4. usage (optional) - displays builder image usage information

Additionally for the best user experience and optimized sti operation we suggest image to have /bin/sh and tar command inside.

Users can also set extra environment variables in the application source code, which are passed to the build and the assemble script consumes them. All environment variables are also present in the output application image. These variables are defined in .sti/environment file inside the application sources. The format of this file is a simple key-value, for example:

FOO=bar

In this case, the value of FOO environment variable will be set to bar.

For detailed description of the requirements and the scripts along with examples see builder_image.md

Build workflow

sti build workflow is:

1. sti creates a container based on the build image and passes it a tar file that contains:
   1. The application source in src
   2. The build artifacts in artifacts (if applicable - see incremental builds)
2. sti sets the environment variables from .sti/environment (optional)
3. sti starts the container and runs its assemble script
4. sti waits for the container to finish
5. sti commits the container, setting the CMD for the output image to be the run script and tagging the image with the name provided.

Using ONBUILD images

In case you want to use one of the official Docker language stack images for your build you don't have do anything extra. The STI is capable to recognize the Docker image with ONBUILD instructions and choose the OnBuild strategy. This strategy will trigger all ONBUILD instructions and execute the assemble script (if it exists) as the last instruction.

Since the ONBUILD images usually don't provide any entrypoint, in order to use this build strategy you have to provide it. You can either include the 'run', 'start' or 'execute' script in your application source root folder or you can specify a valid STI scripts URL and the 'run' script will be fetched and set as an entrypoint in that case.

Incremental builds

sti automatically detects:

• Whether a builder image is compatible with incremental building
• Whether a previous image exists, with the same name as the output name for this build

If a save-artifacts script exists, a prior image already exists, and the --clean option is not used, the workflow is as follows:

1. sti creates a new docker container from the prior build image
2. sti runs save-artifacts in this container - this script is responsible for streaming out a tar of the artifacts to stdout
3. sti builds the new output image:
   1. The artifacts from the previous build will be in the artifacts directory of the tar passed to the build
   2. The build image's assemble script is responsible for detecting and using the build artifacts

NOTE: The save-artifacts script is responsible for streaming out dependencies in a tar file.

Dependencies

1. Docker
2. Go

Installation

Assuming go and docker are installed and configured, execute the following commands:

$ go get github.com/openshift/source-to-image
$ cd ${GOPATH}/src/github.com/openshift/source-to-image
$ export PATH=$PATH:${GOPATH}/src/github.com/openshift/source-to-image/_output/local/go/bin/
$ hack/build-go.sh

Getting Started

You can start using sti right away (see releases) with the following test sources and publicly available images:

$ sti build git://github.com/pmorie/simple-ruby openshift/ruby-20-centos7 test-ruby-app
$ docker run --rm -i -p :9292 -t test-ruby-app

$ sti build git://github.com/bparees/openshift-jee-sample openshift/wildfly-8-centos test-jee-app
$ docker run --rm -i -p :8080 -t test-jee-app

Interested in more advanced sti usage? See cli.md for detailed CLI description with examples.