Buildkite Agent Hooks

Hooks extend or override the built-in behaviours of the Buildkite agent and Bootstrap binaries.

Hooks can be defined in the following locations:

• On the agent
• In your pipeline's repository
• In plugins applied to steps

For example, you could define an agent-wide checkout hook which speeds up a fresh git clone on a new build machine, a repository pre-command hook which sets up repository-specific environment variables, or a plugin environment hook which fetches API keys from a secrets' storage service.

There are two categories of hook:

• Agent Lifecycle
• Job Lifecycle

Agent lifecycle hooks are executed by the Buildkite agent as part of the agent's lifecycle. For example, the pre-bootstrap hook is executed before starting a job's bootstrap process, and the agent-shutdown hook is executed before the agent process terminates.

Job lifecycle hooks are sourced by the Buildkite bootstrap in the different job phases. They are run in a per-job shell environment, and any exported environment variables are carried to the job's subsequent phases and hooks. For example, the environment hook can modify or export new environment variables for the job's subsequent checkout and command phases. Shell options set by individual hooks, such as set -e -o pipefail, are not carried over to other phases or hooks.

In August 2021 we changed how we refer to agent hooks to differentiate between the hooks feature for both the agent and bootstrap processes, and the agent hooks-path configuration for the directory that agent level hooks are defined.

Hook locations

Hooks can be defined in three locations:

• Agent hooks - these exist on the agent file system in a directory created by your agent installer and configured by the hooks-path setting. You can define both agent lifecycle and job lifecycle hooks in the agent hooks location. Job lifecycle hooks defined here will be run for every job the agent receives, from any pipeline.
• Repository hooks - these exist in your pipeline repository's .buildkite/hooks directory and can define job lifecycle hooks. Job lifecycle hooks defined here will be run for every pipeline that uses the repository.
• Plugin hooks - these are provided by any plugins you've included in your pipeline steps and can define job lifecycle hooks. Job lifecycle hooks defined by a plugin will only be run for the step that includes them. Plugins can be vendored (if they are already present in the repository, and included using a relative path) or non-vendored (when they are included from elsewhere), which affects the order they are run in.

Agent hooks

Every agent installer creates a hooks directory containing a set of sample hooks. You can find the location of your agent hooks directory in your platform's installation documentation.

To get started with agent hooks copy the relevant example script and remove the .sample file extension.

See agent lifecycle hooks and job lifecycle hooks for the hook types that can be defined in the agent hooks directory.

Repository hooks

Repository hooks allow you to execute repository-specific scripts. Repository hooks live alongside your repository's source code under the .buildkite/hooks directory.

To get started, create a shell script in .buildkite/hooks named post-checkout. It will be sourced and run after your repository has been checked out as part of every job for any pipeline that uses this repository.

You can define any of the job lifecycle hooks whose Order includes Repository.

Plugin hooks

Plugin hooks allow plugins you've defined in your Pipeline Steps to override default behavior.

See the plugin documentation for how to implement plugin hooks and job lifecycle hooks for the list of hook types that a plugin can define.

Agent lifecycle hooks

Creating agent lifecycle hooks

The Buildkite agent executes agent lifecycle hooks. These hooks can only be defined in the agent hooks-path directory. Agent lifecycle hooks can be executables written in any programming language. On Unix-like systems (such as Linux and macOS), hooks must be files that are executable by the user the agent is running as.

Use agent lifecycle hooks to prepare for or clean up after all jobs that may run. For example, use pre-bootstrap to block unwanted jobs from running or use agent-shutdown to tear down a service after all jobs are finished. If your hook uses details about any individual job to run, prefer job lifecycle hooks for those tasks instead.

The agent exports few environment variables to agent lifecycle hooks. Read the agent lifecycle hooks table for details on the interface between the agent and each hook type.

Job lifecycle hooks

The following is a complete list of available job hooks, and the order in which they are run as part of each job:

Creating job lifecycle hooks

Job lifecycle hooks are sourced for every job an agent accepts. Use job lifecycle hooks to prepare for jobs, override default behavior, or clean up after jobs that have finished. For example, use the environment hook to set a job's environment variables or the pre-exit hook to delete temporary files and remove containers. If your hook is related to the startup or shutdown of the agent, consider agent lifecycle hooks for those tasks instead.

Job lifecycle hooks have access to all the standard Buildkite environment variables.

Job lifecycle hooks are copied to $TMPDIR directory and sourced by the agent's default shell. This has a few implications:

• $BASH_SOURCE contains the location the hook is sourced from
• $0 contains the location of the copy of the script that is running from $TMPDIR
• the shebang line of the hook script has no effect

To write job lifecycle hooks in another programming language, you need to execute them from within the shell script, and explicitly pass any Buildkite environment variables you need to the script when you call it.

The following is an example of an environment hook which exports a GitHub API key for the pipeline's release build step:

set -eu
echo '--- :house_with_garden: Setting up the environment'

export GITHUB_RELEASE_ACCESS_KEY='xxx'

Job hooks on Windows

Buildkite defaults to using the Batch shell on Windows. Buildkite agents running on Windows require that either:

• The hooks files have a .bat extension, and be written in Windows Batch, or
• The agent shell option points to the PowerShell or PowerShell Core executable, and the hooks files are written in PowerShell. PowerShell hooks are supported in Buildkite agent version 3.32.3 and above.

An example of a Windows environment.bat hook:

@ECHO OFF
ECHO "--- :house_with_garden: Setting up the environment"
SET GITHUB_RELEASE_ACCESS_KEY='xxx'