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[#]: subject: "Dynamic scheduling of Tekton workloads using Triggers"
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[#]: via: "https://opensource.com/article/21/11/kubernetes-dynamic-scheduling-tekton"
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[#]: author: "Savita Ashture https://opensource.com/users/savita-ashture"
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[#]: collector: "lujun9972"
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[#]: translator: " "
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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Dynamic scheduling of Tekton workloads using Triggers
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======
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Upgrade your CI/CD pipeline with this Kubernetes-native application.
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![Parts, modules, containers for software][1]
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[Tekton][2] is a Kubernetes-native continuous integration and delivery (CI/CD) framework. It allows you to create containerized, composable, and configurable workloads declaratively through Kubernetes Custom Resource Definitions (CRD).
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[Tekton Triggers][3] is a Tekton component that allows you to detect and extract information from events from various sources and execute [TaskRuns][4] and [PipelineRuns][5] based on that information. It also enables passing extracted information to TaskRuns and PipelineRuns from events.
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This article demonstrates how Tekton Triggers integrates with external services, such as a Git repository, using GitLab as an example.
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### Prerequisites
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If you want to follow the steps in this article, you must have a Kubernetes cluster running Kubernetes 1.18 or above with an ingress controller installed that can give you an external IP. You must also have [Tekton Pipelines][6] and [Tekton Triggers][7] installed.
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### Triggers flow
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A Trigger works because Tekton, using a special pod called an EventListener, is able to monitor your cluster for a specific event. To pick up on relevant events, you can use a ClusterInterceptor. When an event occurs that you have identified as significant, the Tekton Trigger starts an action or workflow you have defined.
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![A flow chart showing the interactions among EventListener, Trigger, and ClusterInterceptor.][8]
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Credits: <https://github.com/tektoncd/triggers/blob/main/images/TriggerFlow.svg>
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Tekton Trigger allows you to create a special resource called an EventListener, which is a Kubernetes service that listens for incoming HTTP requests from different sources, usually a Git repository, including those hosted on GitLab, GitHub, and others. Based on those events, the EventListener pod performs actions and creates Tekton resources, such as TaskRun or PipelineRun.
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All Triggers resource definitions are created in YAML, the configuration format most commonly used in Kubernetes. However, before writing YAML files to define a Trigger, it's important to understand Tekton Triggers terminology.
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#### EventListener
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An [EventListener][9] is a Kubernetes service that listens for incoming HTTP requests and executes a Trigger. For example, after receiving a specific incoming request, this definition executes the `gitlab-listener-trigger` Trigger:
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```
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apiVersion: triggers.tekton.dev/v1beta1
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kind: EventListener
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metadata:
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name: gitlab-event-listener
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spec:
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serviceAccountName: gitlab-listener-sa
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triggers:
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- triggerRef: gitlab-listener-trigger
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resources:
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kubernetesResource:
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serviceType: NodePort
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```
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#### Trigger
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A [Trigger][10] decides what to do with a received event. It also sets a TriggerBinding, TriggerTemplate, and optional interceptors to run. Triggers make use of interceptors to validate or modify incoming requests before proceeding.
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```
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apiVersion: triggers.tekton.dev/v1beta1
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kind: Trigger
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metadata:
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name: gitlab-listener-trigger
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spec:
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interceptors:
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- name: "verify-gitlab-payload"
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ref:
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name: "gitlab"
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kind: ClusterInterceptor
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params:
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- name: secretRef
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value:
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secretName: "gitlab-secret"
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secretKey: "secretToken"
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- name: eventTypes
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value:
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- "Push Hook"
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bindings:
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- ref: binding
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template:
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ref: template
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```
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#### Interceptor
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An [interceptor][11] is an event processor that runs before the TriggerBinding. It also performs payload filtering, verification (using a secret), and transformation; defines and tests trigger conditions; and implements other useful processing.
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By default, four core interceptors are installed when installing Triggers: GitHub, GitLab, Bitbucket, and CEL. The installation also includes one Webhook interceptor for implementing custom business logic.
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##### GitLab interceptors
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GitLab interceptors help to validate and filter GitLab webhooks and filter incoming events by event type. The GitLab interceptor requires a secret token. This token is set when creating the webhook in GitLab and is validated by the GitLab interceptor when the request arrives.
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```
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apiVersion: v1
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kind: Secret
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metadata:
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name: gitlab-secret
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type: Opaque
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stringData:
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secretToken: "1234567"
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```
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#### TriggerBinding
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After validating and modifying the incoming request, you need to extract values from the request and bind them to variables that you can later use in a TriggerTemplate to pass our Pipeline.
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For our example, you just need a URL and a revision.
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```
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apiVersion: triggers.tekton.dev/v1beta1
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kind: TriggerBinding
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metadata:
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name: binding
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spec:
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params:
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- name: gitrevision
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value: $(body.checkout_sha)
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- name: gitrepositoryurl
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value: $(body.repository.git_http_url)
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```
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#### TriggerTemplate
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The [TriggerTemplate][12] is a blueprint that instantiates `TaskRun` or `PipelineRun` when EventListener detects an event.
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```
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apiVersion: triggers.tekton.dev/v1beta1
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kind: TriggerTemplate
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metadata:
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name: template
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spec:
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params:
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- name: gitrevision
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- name: gitrepositoryurl
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resourcetemplates:
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- apiVersion: tekton.dev/v1alpha1
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kind: TaskRun
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metadata:
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generateName: gitlab-run-
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spec:
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taskSpec:
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inputs:
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resources:
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- name: source
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type: git
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steps:
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- image: ubuntu
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script: |
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#! /bin/bash
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ls -al $(inputs.resources.source.path)
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inputs:
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resources:
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- name: source
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resourceSpec:
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type: git
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params:
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- name: revision
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value: $(tt.params.gitrevision)
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- name: url
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value: $(tt.params.gitrepositoryurl)
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```
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Note that the pipeline resources module is, at the time of writing, being deprecated and will be replaced by [git-clone][13] tasks, from [tektoncd/catalog][14].
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### Dynamically schedule workloads by configuring a webhook
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First, create a new namespace, `demo`:
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```
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`$ kubectl create ns demo`
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```
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Next, before applying the Triggers resource, configure the required role-based access control (RBAC):
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```
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$ kubectl -n demo apply -f \
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"<https://gist.githubusercontent.com/savitaashture/596bc4d93ff6b7606fe52aa20ba1ba14/raw/158a5ed0dc30fd1ebdac461147a4079cd6187eac/triggers-rbac.yaml>"
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```
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Note: RBAC configurations vary depending on the permissions.
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Apply Triggers resources:
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```
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$ kubectl -n demo apply -f \
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"<https://gist.githubusercontent.com/savitaashture/8aa013db1cb87f5dd1f2f96b0e121363/raw/f4f592d8c1332938878c5ab9641e350c6411e2b0/triggers-resource.yaml>"
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```
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After applying, verify the successful creation of the EventListener object and pod:
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EL object READY status should be **True. **
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```
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$ kubectl get el -n demo
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NAME ADDRESS AVAILABLE REASON READY REASON
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gitlab-event-listener <http://el-gitlab-event-listener.demo.svc.cluster.local:8080> True MinimumReplicasAvailable True
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```
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EL Pod status should be **Running.**
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```
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$ kubectl get pods -n demo
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NAME READY STATUS RESTARTS AGE
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el-gitlab-event-listener-fb77ff8f7-p5wnv 1/1 Running 0 4m22s
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```
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Create ingress to get the external IP to configure in the GitLab webhook:
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```
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$ kubectl -n demo apply -f \
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"<https://gist.githubusercontent.com/savitaashture/3b3554810e391477feae21bb8a9af93a/raw/56665b0a31c7a537f9acbb731b68a519be260808/triggers-ingress.yaml>"
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```
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Get the ingress IP:
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```
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$ kubectl get ingress triggers-ingress-resource -n demo
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NAME CLASS HOSTS ADDRESS PORTS AGE
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ingress-resource <none> * <address> 80 6s
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```
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Configure a webhook in GitLab. In your GitLab repository, go to **Settings -> Webhooks**.
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Then set the below fields:
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* URL: external IP Address from the Ingress with `/` path
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* Secret token: 1234567, which should match the secret value created above from `triggers-resource.yaml` file
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Choose event type from the Trigger section, then just select **Push events,** uncheck **Enable SSL verification**, and click on **Add webhook.**
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![screenshot of GitLab Webhooks configurations][15]
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Savita Ashture, [CC BY-SA 4.0][16]
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#### Testing GitLab events by pushing PR
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Clone your own GitLab repository, make changes, and push. For example:
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```
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$ git clone <https://gitlab.com/savitaashture1/gitlabtest-triggers>
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$ cd gitlabtest-triggers
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$ git commit -m "empty-commit" --allow-empty && git push origin main
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[main 934ecba] empty-commit
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Username for '<https://gitlab.com>': savitaashture
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Password for '<https://savitaashture@gitlab.com>':
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warning: redirecting to <https://gitlab.com/savitaashture1/gitlabtest-triggers.git/>
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Enumerating objects: 1, done.
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Counting objects: 100% (1/1), done.
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Writing objects: 100% (1/1), 183 bytes | 183.00 KiB/s, done.
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Total 1 (delta 0), reused 0 (delta 0)
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To <https://gitlab.com/savitaashture1/gitlabtest-triggers>
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ff1d11e..934ecba main -> main
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```
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Events will be generated and sent to the EventListener pod. You can verify this by doing:
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```
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kubectl get pods -n demo
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kubectl logs -f <pod_name> -n demo
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```
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Verify successful delivery of events by doing a `get` operation for `TaskRun`.
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```
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$ kubectl -n demo get taskruns | grep gitlab-run-
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gitlab-run-hvtll True Succeeded 95s 87s
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```
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Clean all resources created by Triggers by removing namespace `demo`:
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`$ kubectl delete ns demo`
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### Conclusion
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Tekton Triggers is one of the most useful modules that help schedule workloads dynamically in response to a user-defined set of events. Because of this module, my team was able to achieve end-to-end CI/CD.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/11/kubernetes-dynamic-scheduling-tekton
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作者：[Savita Ashture][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/savita-ashture
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/containers_modules_networking_hardware_parts.png?itok=rPpVj92- (Parts, modules, containers for software)
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[2]: https://opensource.com/article/21/11/cicd-pipeline-kubernetes-tekton
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[3]: https://github.com/tektoncd/triggers
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[4]: https://github.com/tektoncd/pipeline/blob/master/docs/taskruns.md
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[5]: https://github.com/tektoncd/pipeline/blob/master/docs/pipelineruns.md
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[6]: https://github.com/tektoncd/pipeline/blob/main/docs/install.md#installing-tekton-pipelines-on-kubernetes
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[7]: https://github.com/tektoncd/triggers/blob/main/docs/install.md#installing-tekton-triggers-on-your-cluster
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[8]: https://opensource.com/sites/default/files/uploads/tekton_event_chart.png (Trigger flow)
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[9]: https://github.com/tektoncd/triggers/blob/main/docs/eventlisteners.md
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[10]: https://github.com/tektoncd/triggers/blob/main/docs/triggers.md
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[11]: https://github.com/tektoncd/triggers/blob/main/docs/interceptors.md
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[12]: https://github.com/tektoncd/triggers/blob/main/docs/triggertemplates.md
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[13]: https://github.com/tektoncd/catalog/blob/main/task/git-clone/0.4/git-clone.yaml
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[14]: https://github.com/tektoncd/catalog
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[15]: https://opensource.com/sites/default/files/uploads/tekton_trigger_screenshot.png (GitLab repository)
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[16]: https://creativecommons.org/licenses/by-sa/4.0/
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