Enable skipping pipeline steps based on some condition expression (CEL)

[kispaljr]

Problem statement

As a kpt package author I want to be able to create a package with a pipeline step (KRM function) that is only executed if some condition based on the contents of the package is true.

E.g. I want to take different steps in the pipeline based on which type of secret management the package is configured to do.

Please note that this is different from filtering the KRM objects that a pipeline step is applied to (selectors and exclude fields).

Workarounds with the current version

I can write my own KRM function that evaluates the condition. However, if the step wouldn't need a custom KRM function otherwise (since I only want to do a set-annotation) this is very uncomfortable, and complicates my package unnecessary.

Possible solution

Add an "execution condition" field to the Pipeline schema, that can contain a CEL expression referencing the KRM objects in the package.

[SurbhiAgarwal1]

Hey! I'd like to take this one if it's still available.

I've been looking through the issue and the codebase, and this seems like a really useful feature. The workaround of writing a custom function just to check a condition is definitely awkward when you just want to do something simple like set-annotation.

Here's what I'm thinking for the implementation:

Approach:

• Add a condition field to the Function struct in the pipeline schema
• Use the CEL library (google/cel-go) for evaluating expressions
• The runner will check the condition before executing each function
• If condition evaluates to false, skip the function (just pass through the input unchanged)

Example of what it would look like:

pipeline:
  mutators:
  - image: gcr.io/kpt-fn/set-namespace:v0.4
    condition: "resources.exists(r, r.kind == 'ConfigMap' && r.metadata.name == 'env-config')"
    configMap:
      namespace: production

I'll start with the schema changes and get CEL integrated into the runner. Should have something working soon.

Let me know if there are any specific considerations I should keep in mind!