Safely allowing cross namespace references

[Rob Scott]

Hey sig-auth,

I wanted to get your feedback on a design we have added to Gateway API that will enable some cross namespace references. In our case, we have a common scenario where users want to configure their load balancing infrastructure in an infra namespace and use that to route to apps in different namespaces.

To accomplish this safely, we introduced a handshake mechanism. One side of that handshake is a direct object reference to a resource in a different namespace. The other side of that handshake is a ReferencePolicy in the target namespace. Users can create ReferencePolicy resources in namespaces they control to allow references from other namespaces.

Each ReferencePolicy has 2 sections - from (group, kind, namespace), and to (group, kind). This lets a user allow references from Routes in an infra namespace to Services in their local namespace.

We've received feedback that this pattern could be useful beyond just Gateway API. For example, the Storage Bucket KEP could also use a resource like this. 

I've added this topic to the agenda for this week's sig-auth community meeting, but thought this email might help to get the discussion going.

Thanks!

Rob

[Tim Hockin]

Another example would be cross-namespace secrets - it has been asked a hundred times.

Another example would be cross-namespace Ingress - which was a CVE not too long ago.

In short, this keeps coming up, and I would like to see a consistent answer to it.  Namespace is a 95% perfect solution.  The other 5% is fraught.  

This approach doesn't seem awful to me, but I am not an expert in this area at all, and I can't say what other models might work as well or better.

Looking forward to a consult :)

Tim 

[Tasha Drew]

Adding the @kubernetes-wg-multitenancy to the thread, good convo

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