updates/deletes to unrelated Services trigger DAG rebuilds

[skriss]

Spun out from #4386, it looks like the same thing happens for Services since we are not calling serviceTriggersRebuild on removals (which happen for both updates and deletes).

[skriss]

Adding to 1.24 to be tackled along with the Secrets work.

[vishal-chdhry]

Hi! @skriss I would love to contribute but I can't understand what I have to do. Can you please guide me a little

[skriss]

Hey @vishal-chdhry! Here's some more detail, let me know if you have further questions.

#4792 did something similar, but for Secrets -- it's a good template to follow.

When we insert a Service into the DAG cache, we call kc.serviceTriggersRebuild to see if the DAG needs to be rebuilt (https://github.com/projectcontour/contour/blob/main/internal/dag/cache.go#L112). However, when we update/delete a Service, we are not performing that same check (https://github.com/projectcontour/contour/blob/main/internal/dag/cache.go#L263-L267). We need to add that check to the remove logic.

We should also ensure that https://github.com/projectcontour/contour/blob/main/internal/dag/cache_test.go#L953 has test cases for both (a) deleting a Service that is referenced by an HTTPProxy, which should trigger a rebuild; and (b) deleting a Service that is not referenced, which should not trigger a rebuild.

https://github.com/projectcontour/contour/blob/main/internal/featuretests/v3/cluster_test.go#L622 would also be good to add to, to ensure that updating/deleting the Service does not trigger xDS traffic. You can look at https://github.com/projectcontour/contour/pull/4792/files#diff-39afe30b2f5c7952f94cbdcd0e39f1d985f3ed59b9d292100637eb82a1f21c6a for an example of how something similar was tested for Secrets.

[vishal-chdhry]

\assign