📣 Are you using when expressions? 📣

[jerop]

Hello Tekton Friends!

This discussion is about changes to when expressions in Tekton Pipelines 0.27.

We are migrating to using when expressions to guard a Task only. For further details, read the proposal in TEP-0059: Skipping Strategies.

Set scope-when-expressions-to-task field in feature flags to "true" enable the new functionality.

Guard a Task only

When guarding a Task only, its:

• ordering-dependent Tasks, based on runAfter, will be executed
• resource-dependent Tasks will be attempted and:
  • if based on Results, the dependent Tasks will be skipped due to missing Results
    • further dependent Tasks will be skipped as well
    • when we support default Results, these resource-dependent Tasks would be executed if default Results are specified, read more in TEP-0048
  • if based on Workspaces, make sure to handle the execution of the dependent Task in case the file expected from the skipped parent Task is missing from the Workspace

Read more in Guard a Task only.

Guard a Task and its dependent Tasks

To guard a Task and its dependent Tasks, there are two options:

• cascade the when expressions to the specific dependent Tasks to be guarded as well
• compose the Task and its dependent Tasks as a unit to be guarded and executed together using Pipelines in Pipelines (experimental feature), read more in TEP-0056

Read more in Guard a Task and its dependent Tasks.

Example

In the example below, manual-approval Task is executed only when merging a pull request, which is guarded using when expressions. To reuse the Pipeline when merging and not merging, the dependent Tasks need to be executed when the guarded manual-approval Task is skipped.

Previously, if the when expressions in manual-approval were evaluated to "false", then manual-approval, build-image, deploy-image and slack-msg Tasks would all be skipped.

With scoping when expressions to Task, then build-image and deploy-image would be executed. For now, slack-msg would be skipped because of the missing approver Result - but should be executed if you provide default Results when we support them.

Timeline

In February 2022, this flag will be flipped to "true" and then it’ll be removed in March 2022. Read more in Deprecations and TEP-0059: Skipping Strategies - Migration.

Happy to answer any questions here or elsewhere. I’ll follow up with updates and reminders on this migration.

Thanks,
Jerop

[afrittoli]

The flag default value was switched as part of release v0.33.x