Tekton Triggers with GitHub

Tekton Triggers allow us to automate the instantiation of pipelines based on external events. This means, for instance, we can start a pipeline every time a new pull request is created in our GitHub repository. This is the power of CI/CD in action!

Before we can create a trigger we need to install tekton, triggers and interceptors

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

First we need to create the service account and the permissions:

apiVersion: v1
kind: ServiceAccount
metadata:
  name: tekton-service-account
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: tekton-triggers-minimal
rules:
# EventListeners need to be able to fetch all namespaced resources
- apiGroups: ["triggers.tekton.dev"]
  resources: ["eventlisteners", "triggerbindings", "triggertemplates", "triggers", "interceptors"]
  verbs: ["get", "list", "watch"]
- apiGroups: [""]
# configmaps is needed for updating logging config
  resources: ["configmaps"]
  verbs: ["get", "list", "watch"]
# Permissions to create resources in associated TriggerTemplates
- apiGroups: ["tekton.dev"]
  resources: ["pipelineruns", "pipelineresources", "taskruns"]
  verbs: ["create"]
- apiGroups: [""]
  resources: ["serviceaccounts"]
  verbs: ["impersonate"]
- apiGroups: ["policy"]
  resources: ["podsecuritypolicies"]
  resourceNames: ["tekton-triggers"]
  verbs: ["use"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: tekton-triggers-binding
subjects:
- kind: ServiceAccount
  name: tekton-service-account
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: tekton-triggers-minimal
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: tekton-triggers-clusterrole
rules:
  # EventListeners need to be able to fetch any clustertriggerbindings
- apiGroups: ["triggers.tekton.dev"]
  resources: ["clustertriggerbindings", "clusterinterceptors", "interceptors"]
  verbs: ["get", "list", "watch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: tekton-triggers-clusterbinding
subjects:
- kind: ServiceAccount
  name: tekton-service-account
  namespace: default
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: tekton-triggers-clusterrole

That we apply with

kubectl apply -f rbac.yaml

After that we are going to create the pipeline that we will use later when we trigger the event.

apiVersion: tekton.dev/v1beta1
kind: Pipeline
metadata:
  name: github-echo-pipeline
spec:
  tasks:
  - name: echo-message
    taskSpec:
      steps:
      - name: echo
        image: ubuntu
        script: |
          #!/bin/bash
          echo "Pipeline triggered by a GitHub pull request!"

Let’s execute with

kubectl apply -f pipelines.yaml

Now we check the pipeline with

tkn pipeline list

Triggers in Tekton mainly consist of three components:

1. TriggerBinding: Extracts data from the event payload.

2. TriggerTemplate: Uses the data to create Tekton resources.

3. EventListener: Listens for the external events."

Our EventListener will listen for GitHub webhook events and use the TriggerBinding and TriggerTemplate to execute our pipeline.

apiVersion: triggers.tekton.dev/v1beta1
kind: EventListener
metadata:
  name: github-pr
spec:
  serviceAccountName: tekton-service-account
  triggers:
    - name: pr-trigger
      bindings:
        - ref: github-pr-trigger-binding
      template:
        ref: github-pr-trigger-template
  resources:
    kubernetesResource:
      serviceType: LoadBalancer

Now we execute

kubectl apply -f evenlistener.yaml

We can check with

tkn eventlistener list

Now we get the service with

kubectl get svc

And we check the pod created with

kubectl get pods

Let's define our TriggerBinding to extract the necessary information from GitHub's webhook payload

apiVersion: triggers.tekton.dev/v1beta1
kind: TriggerBinding
metadata:
  name: github-pr-trigger-binding
spec:
  params:
  - name: revision
    value: $(body.pull_request.head.sha)
  - name: repo-url
    value: $(body.repository.clone_url)

This binding extracts the git revision and repository URL from the event

kubectl apply -f trigerbinding.yaml

Now we check the pipeline with

tkn triggerbinding list

Now, let's define how the extracted data will be used to instantiate our pipeline

apiVersion: triggers.tekton.dev/v1beta1
kind: TriggerTemplate
metadata:
  name: github-pr-trigger-template
spec:
  params:
  - name: revision
    default: main
  - name: repo-url
  resourcetemplates:
  - apiVersion: tekton.dev/v1beta1
    kind: PipelineRun
    metadata:
      generateName: my-pipeline-
    spec:
      pipelineRef:
        name: github-echo-pipeline
      params:
      - name: repo-url
        value: $(tt.params.repo-url)
      - name: revision
        value: $(tt.params.revision)

This template will create a unique PipelineRun for each event using the $(uid) variable.

kubectl apply -f trigger.yaml

And now we can check the event trigger with

tkn triggertemplate list

Now we are going to need to know how connect to this trigger and to do that we are going to use the Load Balancer service that was created when the eventlistener was created.

curl -vvv http://IP:8080

Next step is setup GitHub with this IP to the event listener

Go to your GitHub repository:

1. Navigate to Settings > Webhooks > Add webhook.

2. Paste the ngrok URL into the Payload URL field.

3. Set the Content type to application/json.

4. For events, select Pull requests.

5. Save the webhook.

Let's test our setup. Create a new pull request in your GitHub repository. This should automatically trigger

When the PR is create if we execute

tkn pipeline list

We can see that the pipeline has started and it is running and after a few seconds if we check again pipeline is done and Succeeded. Now we can see the logs with

tkn pipeline logs

And as you can see our echo in the pipeline has been executed!

We hope you found this tutorial insightful. Until next time, happy coding!

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Here' the same article in video form for your convenience:

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