Getting Started with Triggers

Create and run your first Tekton Trigger.

This tutorial shows you how to

Install Tekton Triggers.
Create a TriggerTemplate.
Create a TriggerBind.
Create an EventListener.

This guide uses a local cluster with minikube.

Before you begin

Complete the two previous Getting Started tutorials: Tasks and Pipelines. Do not clean up your resources, skip the last section.
Install curl if it’s not already available on your system.

Overview

You can use Tekton Triggers to modify the behavior of your CI/CD Pipelines depending on external events. The basic implementation you are going to create in this guide comprises three main components:

An EventListener object that listens to the world waiting for “something” to happen.
A TriggerTemplate object, which configures a PipelineRun when this event occurs.
A TriggerBinding object, that passes the data to the PipelineRun created by the TriggerTemplate object.

Triggers flow diagram

An optional ClusterInterceptor object can be added to validate and process event data.

You are going to create a Tekton Trigger to run the hello-goodbye Pipeline when the EventListener detects an event.

Install Tekton Triggers

Use kubectl to install Tekton Triggers:

kubectl apply --filename \
https://storage.googleapis.com/tekton-releases/triggers/latest/release.yaml
kubectl apply --filename \
https://storage.googleapis.com/tekton-releases/triggers/latest/interceptors.yaml

Monitor the installation:

kubectl get pods --namespace tekton-pipelines --watch

When tekton-triggers-controller, tekton-triggers-webhook, and tekton-triggers-core-interceptors show 1/1 under the READY column, you are ready to continue. For example:

NAME                                                 READY   STATUS    RESTARTS        AGE
tekton-pipelines-controller-68b8d87687-8mzvt         1/1     Running   2 (4d13h ago)   4d19h
tekton-pipelines-webhook-6fb6dd6d75-7jfz6            1/1     Running   2 (104s ago)    4d19h
tekton-triggers-controller-74b654c6bc-24ds7          1/1     Running   2 (104s ago)    4d19h
tekton-triggers-core-interceptors-79f4dbb969-sk2dk   1/1     Running   3 (104s ago)    4d19h
tekton-triggers-webhook-56885c9875-nx499             1/1     Running   2 (104s ago)    4d19h

Hit Ctrl + C to stop monitoring.

Create a TriggerTemplate

A TriggerTemplate defines what happens when an event is detected.

Create a new file named trigger-template.yaml and add the following:

apiVersion: triggers.tekton.dev/v1beta1
kind: TriggerTemplate
metadata:
  name: hello-template
spec:
  params:
  - name: username
    default: "Kubernetes"
  resourcetemplates:
  - apiVersion: tekton.dev/v1beta1
    kind: PipelineRun
    metadata:
      generateName: hello-goodbye-run-
    spec:
      pipelineRef:
        name: hello-goodbye
      params:
      - name: username
        value: $(tt.params.username)

The PipelineRun object that you created in the previous tutorial is now included in the template declaration. This trigger expects the username parameter to be available; if it’s not, it assigns a default value: “Kubernetes”.

Apply the TriggerTemplate to your cluster:
```
kubectl apply -f trigger-template.yaml
```

Create a TriggerBinding

A TriggerBinding executes the TriggerTemplate, the same way you had to create a PipelineRun to execute the Pipeline.

Create a file named trigger-binding.yaml with the following content:

apiVersion: triggers.tekton.dev/v1beta1
kind: TriggerBinding
metadata:
  name: hello-binding
spec: 
  params:
  - name: username
    value: $(body.username)

This TriggerBinding gets some information and saves it in the username variable.

Apply the TriggerBinding:
```
kubectl apply -f trigger-binding.yaml
```

Create an EventListener

The EventListener object encompasses both the TriggerTemplate and the TriggerBinding.

Create a file named event-listener.yaml and add the following:

apiVersion: triggers.tekton.dev/v1beta1
kind: EventListener
metadata:
  name: hello-listener
spec:
  serviceAccountName: tekton-robot
  triggers:
    - name: hello-trigger 
      bindings:
      - ref: hello-binding
      template:
        ref: hello-template

This declares that when an event is detected, it will run the TriggerBinding and the TriggerTemplate.

The EventListener requires a service account to run. To create the service account for this example create a file named rbac.yaml and add the following:

apiVersion: v1
kind: ServiceAccount
metadata:
  name: tekton-robot
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: triggers-example-eventlistener-binding
subjects:
- kind: ServiceAccount
  name: tekton-robot
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: tekton-triggers-eventlistener-roles
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: triggers-example-eventlistener-clusterbinding
subjects:
- kind: ServiceAccount
  name: tekton-robot
  namespace: default
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: tekton-triggers-eventlistener-clusterroles

This service account allows the EventListener to create PipelineRuns.

Apply the file to your cluster:
```
kubectl apply -f rbac.yaml
```

Running the Trigger

You have everything you need to run this Trigger and start listening for events.

Create the EventListener:
```
kubectl apply -f event-listener.yaml
```

To communicate outside the cluster, enable port-forwarding:

kubectl port-forward service/el-hello-listener 8080

The output confirms that port-forwarding is working:

kubectl port-forward service/el-hello-listener 8080
Forwarding from 127.0.0.1:8080 -> 8080
Forwarding from [::1]:8080 -> 8080

Keep this service running, don’t close the terminal.

Monitor the Trigger

Now that the EventListener is running, you can send an event and see what happens:

Open a new terminal and submit a payload to the cluster:

curl -v \
   -H 'content-Type: application/json' \
   -d '{"username": "Tekton"}' \
   http://localhost:8080

You can change “Tekton” for any string you want. This value will be ultimately read by the goodbye-world Task.

The response is successful:

< HTTP/1.1 202 Accepted
< Content-Type: application/json
< Date: Fri, 30 Sep 2022 00:11:19 GMT
< Content-Length: 164
<
{"eventListener":"hello-listener","namespace":"default","eventListenerUID":"35dd0858-3692-4bb5-8c4f-1bf6d705bb73","eventID":"1a0a1120-7833-4078-9f30-0e3688f27dde"}
* Connection #0 to host localhost left intact

This event triggers a PipelineRun, check the PipelineRuns on your cluster :

kubectl get pipelineruns

The output confirms the pipeline is working:

NAME                      SUCCEEDED   REASON      STARTTIME   COMPLETIONTIME
hello-goodbye-run         True        Succeeded   24m         24m
hello-goodbye-run-8hckl   True        Succeeded   81s         72s

You see two PipelineRuns, the first one created in the previous guide, the last one was created by the Trigger.

Check the PipelineRun logs. The name is auto-generated adding a suffix for every run, in this case it’s hello-goodbye-run-8hckl. Use your own PiepelineRun name in the following command to see the logs:
```
tkn pipelinerun logs <my-pipeline-run> -f
```
And you get the expected output:
```
[hello : echo] Hello World

[goodbye : goodbye] Goodbye Tekton!
```
Both Tasks completed successfuly. Congratulations!

Clean up

Press Ctrl + C in the terminal running the port-forwarding process to stop it.

Delete the cluster:

minikube delete

The output confirms that the cluster was deleted:

🔥  Deleting "minikube" in docker ...
🔥  Deleting container "minikube" ...
🔥  Removing /home/user/.minikube/machines/minikube ...
💀  Removed all traces of the "minikube" cluster.

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Last modified January 29, 2023: Rework left-hand nav order (dbe0a93)