The buildkite agent is a small, reliable and cross-platform build runner that makes it easy to run automated builds on your own infrastructure. Its main responsibilities are polling buildkite.com for work, running build jobs, reporting back the status code and output log of the job, and uploading the job’s artifacts.

 

How it Works?

 

The agent works by polling Buildkite’s agent API over HTTPS. There is no need to forward ports or provide incoming firewall access, and the agents can be run across any number of machines and networks.

The agent starts by registering itself with Buildkite, and once registered it’s placed into your organization’s agents pool. The agent periodically polls Buildkite looking for new work, waiting to accept an available job.

After accepting a build job the agent will execute the command, streaming back the build script’s output and then posting the final exit status.

Whilst the job is running you can use the buildkite-agent meta-data command to set and get build-wide meta-data, and buildkite-agent artifact for fetching and retrieving binary build-wide artifacts. These two commands allow you to have completely isolated build jobs (similar to a 12 factor web application) but have easy access to shared state and data storage across any number of machines and networks.

 

Customising with Hooks

 

The agent’s behavior can be customized using hooks, which are just shell scripts that exist on your build machines or in each pipeline’s code repository. Hooks can be used to set up secrets as well as overriding default behavior. See the hooks documentation for full details.

 

Signal Handling

 

When a build job is cancelled the agent will send the build job process a SIGTERM signal to allow it to gracefully exit. If the process does not exit within 10 seconds it will be forcefully terminated with a SIGKILL signal.

The agent will also accept SIGTERM directly, and will gracefully exit. After it has processed the current job, it will disconnect and stop accepting jobs.

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