advanced.md

description	keywords	title
Automated builds	automated, build, images	Advanced options for Autobuild and Autotest

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 do not 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.
• CACHE_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:CACHE_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.

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

Override build, test or push commands

Docker Cloud 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.)

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).

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 Cloud allows you to define build environment variables either in the hook files, or from the automated build UI (which you can then reference in hooks).

In the following example, we define a build hook that uses docker build arguments to set the variable CUSTOM based on the value of variable we defined using the Docker Cloud build settings. $DOCKERFILE_PATH is a variable that we provide with the name of the Dockerfile we wish 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 .

Caution: 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.

To learn more about Docker build-time variables, see the docker build documentation.

Two-phase build

If your build process requires a component that is not a dependency for your application, you can use a pre-build hook (refers to the hooks/pre_build file) to collect and compile required components. In the example below, the hook uses a Docker container to compile a Golang binary that is required before the build.

#!/bin/bash
echo "=> Building the binary"
docker run --privileged \
  -v $(pwd):/src \
  -v /var/run/docker.sock:/var/run/docker.sock \
  centurylink/golang-builder

Push to multiple repos

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 / Branch Clones

When Docker Cloud pulls a branch from a source code repository, it performs a shallow clone (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.

Because of this, 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:

    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:

    git fetch --unshallow origin