Triggers and EventListeners

Event Based Triggers for Tekton Pipelines

Tekton Triggers

Tekton Triggers is a Tekton component that allows you to detect and extract information from events from a variety of sources and deterministically instantiate and execute TaskRuns and PipelineRuns based on that information. Tekton Triggers can also pass information extracted from events directly to TaskRuns and PipelineRuns. You install Tekton Triggers on your Kubernetes cluster as an extension to Tekton Pipelines.

How does Triggers work?

Tekton Triggers consists of a controller service that runs on your Kubernetes cluster as well as the following Kubernetes Custom Resource Definitions (CRDs) that extend the functionality of Tekton Pipelines to support events:

  • EventListener - listens for events at a specified port on your Kubernetes cluster. Specifies one or more Triggers.

  • Trigger - specifies what happens when the EventListener detects an event. A Trigger specifies a TriggerTemplate, a TriggerBinding, and optionally, an Interceptor.

  • TriggerTemplate - specifies a template for the TaskRun or PipelineRun you want to instantiate and execute when EventListener detects an event.

  • TriggerBinding - specifies the fields in the event payload from which you want to extract data as well as the fields in your TaskRun or PipelineRun to populate with the extracted values. In other words, it binds payload fields to TaskRun or PipelineRun fields.

  • ClusterTriggerBinding - a cluster-scoped version of the TriggerBinding, especially useful for reuse within your cluster.

  • Interceptor - a “catch-all” event processor for a specific platform that runs before the TriggerBinding enabling you to perform payload filtering, verification (using a secret), transformation, define and test trigger conditions, and other useful processing. Once the event data passes through an interceptor, it then goes to the Trigger before you pass the payload data to the TriggerBinding.

    Note: Interceptors are currently part of EventListeners but are being converted to a standalond CRD in PR 960.

What can I do with Triggers?

As an example, you can implement the following CI/CD workflow with Triggers:

  1. Triggers listens for a git commit or a git pull request event. When it detects one, it executes a unit test Pipeline on the committed code.

  2. Triggers listens for a git push event indicating the test finished successfully. When it detects one, it validates the test’s outcome and executes a Pipeline that builds the tested code.

  3. When the associated PipelineRun completes execution, Triggers checks the outcome of the build, and if it’s successful, executes a Task that uploads the build artifacts to the Docker registry of your choice.

  4. Finally, the Docker registry sends an event to Pub/Sub, which triggers a Pipeline that pushes the build artifacts to a staging environment.

Further Reading

To get started with Tekton Triggers, see the following: