If Cosmo DB NoSQL is using Multi-Region Writes, then it is recommended by Microsoft to not enable Availability Zone support as it provides limited value. As documented in the learn docs. Following the guidance shared in - the learn docs around the impact of using availability zones with Multi-Region Writes enabled. AZs for Multi-Region writes are free, and it is assumed having them turned on doesn't affect the reliability of Cosmo DB when using Multi-Region Writes.
It should be noted that having AZ enabled only is recommended if strong consistency is being used. Multi-Region Writes do not support strong consistency.
Cosmos DB accounts configured with multiple write regions can't be configured for strong consistency as it isn't possible for a distributed system to provide an RPO of zero and an RTO of zero.
ejhenry
commented
4 days ago
Describe the solution you'd like
If Cosmo DB NoSQL is using Multi-Region Writes, then it is recommended by Microsoft to not enable Availability Zone support as it provides limited value. As documented in the learn docs. Following the guidance shared in - the learn docs around the impact of using availability zones with Multi-Region Writes enabled. AZs for Multi-Region writes are free, and it is assumed having them turned on doesn't affect the reliability of Cosmo DB when using Multi-Region Writes.
It should be noted that having AZ enabled only is recommended if strong consistency is being used. Multi-Region Writes do not support strong consistency.
I have also updated the wording in the learn docs to reflect this - https://github.com/MicrosoftDocs/azure-docs/pull/123628
Recommendation: The feature request is two folds: If Multi-Region writes is enabled, then AZs are grayed out, as they provide limited value.
Describe alternatives you've considered
No alternatives
Additional context
All context is added to the above.