Creating a custom builder allows you to control what buildpacks are used and what image apps are based on.
As part of this guide we’ll create a basic builder that uses mostly no-op buildpacks to show you around a bit.
Before we start, let’s pull down a few buildpacks from our samples repo.
# clone the repo git clone https://github.com/buildpacks/samples
First, let’s create a builder configuration file (
builder.toml) with the following contents:
# Buildpacks to include in builder [[buildpacks]] uri = "samples/buildpacks/hello-processes" [[buildpacks]] # Packaged buildpacks to include in builder; # the "hello-universe" package contains the "hello-world" and "hello-moon" buildpacks image = "cnbs/sample-package:hello-universe" # Order used for detection [[order]] # This buildpack will display build-time information (as a dependency) [[order.group]] id = "samples/hello-world" version = "0.0.1" # This buildpack will display build-time information (as a dependant) [[order.group]] id = "samples/hello-moon" version = "0.0.1" # This buildpack will create a process type "sys-info" to display runtime information [[order.group]] id = "samples/hello-processes" version = "0.0.1" # Stack that will be used by the builder [stack] id = "io.buildpacks.samples.stacks.bionic" # This image is used at runtime run-image = "cnbs/sample-stack-run:bionic" # This image is used at build-time build-image = "cnbs/sample-stack-build:bionic"
Creating a builder is now as simple as running the following command:
# create builder pack builder create my-builder:bionic --config ./builder.toml
builder createhas a
--publishflag that can be used to publish the generated builder image to a registry.
Congratulations! You’ve got a custom builder.
Let’s go a little further and use our builder to
build an app by running:
pack build my-app --builder my-builder:bionic --path samples/apps/java-maven/
Remember that we mentioned that the buildpacks we used as part of this builder don’t really do much. To be honest, they
didn’t even use the app source code. What they did do was show the environment in which they run on and now by running
the app image with
--entrypoint sys-info we can see the runtime information as well.
docker run --rm --entrypoint sys-info -it my-app
We’re sure you’ll be able to create more useful builders.
For additional sample builders and buildpacks, check out our samples repo.
You can also check out our reference of the builder config here.
If you would like to customize the stack used by your builder, check out our Create a stack tutorial.