The system I'm working on has multiple environments, each running in separate Azure regions. Our CosmosDB is replicated to these regions and multi-region writes are enabled. We're using the default consistency model (Session).
We have azure functions that use the CosmosDb trigger deployed in all three regions. Currently these use the same lease prefix which means that only one function processes changes at any given time. I know that we can set each region to have different lease prefixes to enable concurrent processing but I'd like to solidify my understanding before taking this step.
My question is around the behaviour of the change feed with regards to replication in this scenario? According to this link https://github.com/MicrosoftDocs/azure-docs/issues/42248#issuecomment-552207409 data is first converged on the primary region and then the change feed is updated.
Other resources I've read seem to suggest that each region has it's own change feed which will update upon replication. Also, the previous link recommends only running a change feed processor in the primary region in multi-master.
In an ideal world, I'd like change feed processors in each region to handle local writes quickly. These functions will make updates to CosmosDB and I also want to avoid issues with replication. My question is - what is the actual behavior in a multi master configuration (and by extension the correct architecture)?. Is it "safe" to use per-region change feed processors, or should we use a single processor in the primary region?
