Buildpacks tutorial

About this project

This project is cloned from Spring PetClinic and its purpose is to showcase how Buildpacks works.

Requirements

• pack CLI installed
• Docker daemon installed

Getting started

First, choose one of the suggested builder from the output of this command:

pack suggest-builders

As this is a Java application, select one with a buildpack for Java, for example cloudfoundry/cnb:bionic. You could choose a builder from another source or even build your own (Create a buildpack and Create a builder).

Once you've chosen a builder, you can build it as follows:

pack build <image-name> --builder <builder-name>

For example:

pack build petclinic:buildpack --builder cloudfoundry/cnb:bionic

From the command output you can determine which buildpacks where involved and which layers where rebuilt. Once your image is built, use docker images to see it and docker run -p 8080:8080 --rm <image-name>:<tag> to run it.

Inspecting an image

Once you have built your image, you can inspect it to see some metadata:

pack inspect-image <image-name>

For example, building this petclinic application with cloudfoundry/cnb:bionic and then inspecting it returns the following output:

REMOTE:
(not present)

LOCAL:

Stack: io.buildpacks.stacks.bionic

Base Image:
 Reference: 1332879bc8e38793a45ebe5a750f2a1c35df07ec2aa9c18f694644a9de77359b
 Top Layer: sha256:eb195d29dc1aa6e4239f00e7868deebc5ac12bebe76104e0b774c1ef29ca78e3

Run Images:
 cloudfoundry/run:base-cnb

Buildpacks:
 ID                                                VERSION
 org.cloudfoundry.openjdk                          v1.2.14
 org.cloudfoundry.buildsystem                      v1.2.15
 org.cloudfoundry.jvmapplication                   v1.1.12
 org.cloudfoundry.tomcat                           v1.3.18
 org.cloudfoundry.springboot                       v1.2.13
 org.cloudfoundry.distzip                          v1.1.12
 org.cloudfoundry.springautoreconfiguration        v1.1.11

Processes:
 TYPE                  SHELL        COMMAND                                                                                          ARGS
 web (default)         bash         java -cp $CLASSPATH $JAVA_OPTS org.springframework.samples.petclinic.PetClinicApplication
 executable-jar        bash         java -cp $CLASSPATH $JAVA_OPTS org.springframework.boot.loader.JarLauncher
 spring-boot           bash         java -cp $CLASSPATH $JAVA_OPTS org.springframework.samples.petclinic.PetClinicApplication
 task                  bash         java -cp $CLASSPATH $JAVA_OPTS org.springframework.samples.petclinic.PetClinicApplication

We can see that the buildpacks used for its building process, the name of the stack used (useful for rebasing our image to another stack) and the reference for the top layer of the stack. You can also use the flag --bom, which returns a bill of materials as a JSON object, with more information about each layer.

Inspecting an image can be done in images generated by Buildpacks, as well as in any other image. Keep in mind other images may not contain this kind of metadata in them.

Documentation

You can access the official Buildpacks documentation here.