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153 lines
5.3 KiB
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[#]: subject: "Create conditional pipelines with CEL"
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[#]: via: "https://opensource.com/article/22/7/conditional-tekton-pipelines-cel"
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[#]: author: "Camilla Conte https://opensource.com/users/spotlesstofu"
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[#]: collector: "lkxed"
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[#]: translator: " "
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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Create conditional pipelines with CEL
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======
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Control when automated builds happen in Tekton with CEL.
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![Plumbing tubes in many directions][1]
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You just followed a guide to start your Tekton pipeline (or task) when a merge request is created or updated on your GitLab project. So you configured GitLab to send merge request **events** as **webhooks**. And you deployed some **Tekton** components:
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* EventListener: receives webhooks from GitLab
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* Trigger: starts your Pipeline every time the EventListener receives a new webhook from GitLab
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* Pipeline: fetches the source code from GitLab and builds it
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Then you notice that any event in your merge request (a new comment, a tag change) triggers the pipeline. That's not the behavior you desire. You don't need to build a comment or a tag, after all. You only want the pipeline to run when there is actual new code to build. Here's how I use Tekton's CEL Interceptor to create conditionals for my pipelines.
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### Have your trigger ready
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I expect you have a trigger already defined. It's probably something similar to the snippet below.
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The trigger's interceptor rejects anything that's not coming from a merge request. Still, the interceptor is not able to differentiate between code and non-code updates (like new comments).
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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: webhook-listener-trigger
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spec:
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interceptors:
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# reject any payload that's not a merge request webhook
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- name: "filter-event-types"
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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: eventTypes
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value:
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- "Merge Request 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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### Add a CEL interceptor
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Here comes the `cel` interceptor. This interceptor filters the webhook payload using the CEL expression language. If the filter expression evaluates to `true`, the pipeline starts.
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Here I'm checking for the `object_attributes.oldrev` field to exist in the JSON body of the webhook payload. If `object_attributes.oldrev` exists, then that means this event is about a code change. If there wasn't a code change, there's no previous revision (`oldrev` ) to refer to.
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```
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spec:
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interceptors:
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- name: "allow-code-changes-only"
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ref:
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name: cel
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kind: ClusterInterceptor
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params:
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- name: filter
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value: >
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has(body.object_attributes.oldrev)
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```
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Add the new interceptor to your trigger. Now your trigger looks like this:
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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: eventTypes
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value:
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- "Merge Request Hook"
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- name: "allow-code-changes-only"
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ref:
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name: "cel"
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kind: ClusterInterceptor
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params:
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- name: filter
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value: >
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has(body.object_attributes.oldrev)
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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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Deploy this new version of the trigger and enjoy the powers of automation. From now on, your pipeline only starts if there is some new code to build.
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### Tips
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There are no limits to the conditions you can set in a CEL filter.
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You may check that the merge request is currently open:
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```
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body.object_attributes.state in ['opened']
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```
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You can make sure the contributor finished their work on the code:
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```
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body.object_attributes.work_in_progress == false
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```
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You just have to concatenate multiple conditions correctly:
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```
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- name: filter
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value: >
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has(body.object_attributes.oldrev) &&
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body.object_attributes.state in ['opened'] &&
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body.object_attributes.work_in_progress == false
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```
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Check out the [merge request events][2] documentation to get inspired to write your own conditions.
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You may need the [CEL language definition][3] to know how to translate your thoughts into code.
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To evaluate types other than strings, you want to know the [mapping between JSON and CEL][4] types.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/22/7/conditional-tekton-pipelines-cel
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作者：[Camilla Conte][a]
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选题：[lkxed][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/spotlesstofu
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[b]: https://github.com/lkxed
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[1]: https://opensource.com/sites/default/files/lead-images/plumbing_pipes_tutorial_how_behind_scenes.png
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[2]: https://docs.gitlab.com/ee/user/project/integrations/webhook_events.html#merge-request-events
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[3]: https://github.com/google/cel-spec/blob/master/doc/langdef.md
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[4]: https://github.com/google/cel-spec/blob/master/doc/langdef.md#json-data-conversion
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