[!NOTE]

Automated builds require a Docker Pro, Team, or Business subscription.

The following options allow you to customize your automated build and automated test processes.

Environment variables for building and testing#

Several utility environment variables are set by the build process, and are available during automated builds, automated tests, and while executing hooks.

[!NOTE]

These environment variables are only available to the build and test processes and don't affect your service's run environment.

• SOURCE_BRANCH: the name of the branch or the tag that is currently being tested.
• SOURCE_COMMIT: the SHA1 hash of the commit being tested.
• COMMIT_MSG: the message from the commit being tested and built.
• DOCKER_REPO: the name of the Docker repository being built.
• DOCKERFILE_PATH: the dockerfile currently being built.
• DOCKER_TAG: the Docker repository tag being built.
• IMAGE_NAME: the name and tag of the Docker repository being built. (This variable is a combination of DOCKER_REPO:DOCKER_TAG.)

If you are using these build environment variables in a docker-compose.test.yml file for automated testing, declare them in your sut service's environment as shown below.

services:
  sut:
    build: .
    command: run_tests.sh
    environment:
      - SOURCE_BRANCH

Override build, test or push commands#

Docker Hub allows you to override and customize the build, test and push commands during automated build and test processes using hooks. For example, you might use a build hook to set build arguments used only during the build process. You can also set up custom build phase hooks to perform actions in between these commands.

[!IMPORTANT]

Use these hooks with caution. The contents of these hook files replace the basic docker commands, so you must include a similar build, test or push command in the hook or your automated process does not complete.

To override these phases, create a folder called hooks in your source code repository at the same directory level as your Dockerfile. Create a file called hooks/build, hooks/test, or hooks/push and include commands that the builder process can execute, such as docker and bash commands (prefixed appropriately with #!/bin/bash).

These hooks run on an instance of Ubuntu, which includes interpreters such as Perl or Python, and utilities such as git or curl. Refer to the Ubuntu documentation for the full list of available interpreters and utilities.

Custom build phase hooks#

You can run custom commands between phases of the build process by creating hooks. Hooks allow you to provide extra instructions to the autobuild and autotest processes.

Create a folder called hooks in your source code repository at the same directory level as your Dockerfile. Place files that define the hooks in that folder. Hook files can include both docker commands, and bash commands as long as they are prefixed appropriately with #!/bin/bash. The builder executes the commands in the files before and after each step.

The following hooks are available:

• hooks/post_checkout
• hooks/pre_build
• hooks/post_build
• hooks/pre_test
• hooks/post_test
• hooks/pre_push (only used when executing a build rule or Automated build )
• hooks/post_push (only used when executing a build rule or Automated build )

Build hook examples#

Override the "build" phase to set variables#

Docker Hub allows you to define build environment variables either in the hook files, or from the automated build interface, which you can then reference in hooks.

The following example defines a build hook that uses docker build arguments to set the variable CUSTOM based on the value of variable defined using the Docker Hub build settings. $DOCKERFILE_PATH is a variable that you provide with the name of the Dockerfile you want to build, and $IMAGE_NAME is the name of the image being built.

$ docker build --build-arg CUSTOM=$VAR -f $DOCKERFILE_PATH -t $IMAGE_NAME .

[!IMPORTANT]

A hooks/build file overrides the basic docker build command used by the builder, so you must include a similar build command in the hook or the automated build fails.

Refer to the docker build documentation to learn more about Docker build-time variables.

Push to multiple repositories#

By default the build process pushes the image only to the repository where the build settings are configured. If you need to push the same image to multiple repositories, you can set up a post_push hook to add additional tags and push to more repositories.

$ docker tag $IMAGE_NAME $DOCKER_REPO:$SOURCE_COMMIT
$ docker push $DOCKER_REPO:$SOURCE_COMMIT

Source repository or branch clones#

When Docker Hub pulls a branch from a source code repository, it performs a shallow clone, it clones only the tip of the specified branch. This has the advantage of minimizing the amount of data transfer necessary from the repository and speeding up the build because it pulls only the minimal code necessary.

As a result, if you need to perform a custom action that relies on a different branch, such as a post_push hook, you can't checkout that branch unless you do one of the following:

• You can get a shallow checkout of the target branch by doing the following:

  console $ git fetch origin branch:mytargetbranch --depth 1

• You can also "unshallow" the clone, which fetches the whole Git history (and potentially takes a long time / moves a lot of data) by using the --unshallow flag on the fetch:

  console $ git fetch --unshallow origin