Inter-cluster resource collisions for gcppubsub bus

[scothis]

Expected Behavior

Each channel on a gcppubsub bus should operate atomically.

Actual Behavior

If there are two Knative clusters running in the same GCP Project, that create a gcppubsub bus with the same name in the same namespace, and a channel is created with the same name, and a subscription is created with the same name. The topics and subscription resources in pub/sub end up being shared between both clusters which assume that have use of those resources exclusively.

This is mostly an issue when running samples, but can cause head scratching.

Steps to Reproduce the Problem

1. create two Knative clusters
2. deploy the gcppubsub bus into each cluster in the same name/namespace using the same GCP Project
3. deploy the hello sample into each cluster
4. each message hitting the bus will only be delivered to one of the clusters (appears to be round robin)

Additional Info

The topic and subscription resources in cloud pub/sub should have a random value representing the bus that "owns" the resource that is also stable for the lifetime of the bus.

/kind bug

[scothis]

/assign @scothis

[vaikas]

@scothis can this be closed or is there something else to do here?

[scothis]

@vaikas-google while the implementation has been completely rewritten, the same bug still exists. The PR was closed because it was pointing at the old bus implementation which had been removed.

The topic name generated for a channel needs to be stable within a given cluster and unique across clusters in order to side-step this bug. The current topic name generator produces names that collide between clusters that use the same Pub/Sub project.

cc @matzew

[scothis]

/unassign @scothis

[matzew]

/assign @matzew

[matzew]

I was not aware of this issue, but will take a look!

[evankanderson]

/assign @Harwayne

Adam was also looking at this; I don't want @matzew and @Harwayne to collide/waste effort.