Build hooks allow behavior to be injected into the build process.
The postCommit field of a BuildConfig object executes commands inside a
temporary container that is running the build output image. The hook is executed
immediately after the last layer of the image has been committed and before the
image is pushed to a registry.
The current working directory is set to the image’s WORKDIR, which is the
default working directory of the container image. For most images, this is where
the source code is located.
The hook fails if the script or command returns a non-zero exit code or if starting the temporary container fails. When the hook fails it marks the build as failed and the image is not pushed to a registry. The reason for failing can be inspected by looking at the build logs.
Build hooks can be used to run unit tests to verify the image before the build is marked complete and the image is made available in a registry. If all tests pass and the test runner returns with exit code 0, the build is marked successful. In case of any test failure, the build is marked as failed. In all cases, the build log will contain the output of the test runner, which can be used to identify failed tests.
The postCommit hook is not only limited to running tests, but can be used
for other commands as well. Since it runs in a temporary container, changes made
by the hook do not persist, meaning that the hook execution cannot affect the
final image. This behavior allows for, among other uses, the installation and
usage of test dependencies that are automatically discarded and will be not
present in the final image.