ChannelProvisioner should be "multi-tenant"

[sebgoa]

Taking the GCP pubsub channel provisioner as an example, it is not multi-tenant.

It assumes one GCP project and only one pubsub service account.

We should be able to run multiple GCP pubsub channel provisioners that could point to different GCP project, and we should be able to create those per namespace.

[Harwayne]

This will interact with #1002.

There are a few possible solutions in the existing Provisioner model:

1. Create multiple ClusterChannelProvisioners. Each one corresponds to a single GCP (project, secret). They are all available in all namespaces.
   • This could either have one dispatcher per CCP, or a single dispatcher shared by all.
2. Create a ChannelProvisioner CRD. This is similar to ClusterChannelProvisioner, but is namespaced. It is usable only in the namespace it exists in. Users install its controller and dispatcher in the same namespace as the CO.
   • I believe the pre-0.2 object model had both Bus and ClusterBus, but it was annoying to handle both. @grantr can you give any greater insight to the problem that caused?
3. Allow individual Channels to provide arguments to select different projects and credentials. They are available in all namespaces.
   • We might be able to use webhooks to do some sort of auth checks, but I'm not sure.
4. gcp-pubsub CCP has a ConfigMap mapping namespace to (project, secret) tuples. This allows each namespace to use a distinct (project, secret).

As written, it sounds like you want 2, is that correct?

[sebgoa]

2. or 3.

[akashrv]

/assign @n3wscott

For GCP pubsub CRD channel, this is already part of the design. Hence just assigning to Scott.

[akashrv]

This will be part of #1214

[vaikas]

this is fixed in the http://github.google.com/google/knative-gcp