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builder-contract.md

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Builders

This document defines Builder images and the conventions to which they are expected to adhere.

What is a Builder?

A Builder image is a special classification for images that run as a part of the Build CRD's steps:.

For example, in the following Build the images, gcr.io/cloud-builders/gcloud and gcr.io/cloud-builders/docker are "Builders".:

spec:
  steps:
  - image: gcr.io/cloud-builders/gcloud
    ...
  - image: gcr.io/cloud-builders/docker
    ...

Typical Builders

A Builder is typically a purpose-built container whose entrypoint is a tool that performs some action and exits with a zero status on success. These entrypoints are often command-line tools, for example, git, docker, mvn, and so on.

Typical builders set their command: (aka ENTRYPOINT) to be the command they wrap and expect to take args: to direct their behavior.

See here and here for more builders.

Atypical Builders

It it possible, although less typical to implement the Builder convention by overriding command: and args: for example:

steps:
- image: ubuntu
  command: ['/bin/bash']
  args: ['-c', 'echo hello $FOO']
  env:
  - name: 'FOO'
    value: 'world'

Specialized Builders

It is also possible for advanced users to create purpose-built builders. One example of this are the "FTL" builders.

What are the Builder conventions?

Builders should expect a Build to implement the following conventions:

  • /workspace: The default working directory will be /workspace, which is a volume that is filled by the source: step and shared across build steps:.

  • /builder/home: This volume is exposed to steps via $HOME.

  • Credentials attached to the Build's service account may be exposed as Git or Docker credentials as outlined here.

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License.