Question/Suggestion: What would it take to make streams versioned like grain interfaces?

[MarkNickeson]

The basic idea is to enable graceful relocation of "internal streaming state" from Version N to Version N+1 silos, avoiding overt disruption associated with shutdown of silos housing active "internal streaming state".

Explicitly: this is not about versioning message state residing within streams.

Ideally:

• Versioned streams would honor version selector and compatibility strategy semantics just like grain interface versioning
• Orleans would auto-manage "internal streaming state" silo-to-silo migration during version updates, similar to how grain interface versioning results in deactivation/reactivation
• Enable architectural and operational reasoning about "what silos hold my stream caching stuff?"
• Provider independent; works seamlessly for any compliant streaming provider.

Thank you!

[ReubenBond]

It's an interesting idea. Placement is currently based on interfaces, but this could be implemented today using a custom attribute on a grain to add a "version" property to the GrainProperties in the ClusterManifest and then when you encounter a message which is intended for a newer version you would call MigrateOnIdle() with a placement hint to migrate the grain to a new silo programmatically, setting the target's SiloAddress in the RequestContext via RequestContext.Set(IPlacementDirector.PlacementHintKey, targetHost). The target silo would be discovered by finding a compatible silo in the ClusterManifest. From the new grain, you would resume stream processing. This functionality could be wrapped up in a more user-friendly interface. We'd need a proposal for that.