Postgres Instance on RDS vs Aurora

Question

I am looking at either setting up Aurora Postgresql or RDS Postgresql instance in AWS.

I would like the db instance to be running in 2 different regions and would like real time replication to be set up. I would also like no downtime for rehydration / patching etc.

Based on what I have read / discussed with colleagues so far , I am under the impression that Aurora Postgresql is the option to choose because RDS needs few minutes of downtime for rehydration and Aurora supports realtime replication of db instance across different regions.

Is my understanding correct and are there any other factors that I should be aware of?

Answer 1

No RDS product supports "real-time" replication across regions. Cross-region replication is always asynchronous.

You can expect to see a higher level of lag time for any Read Replica that is in a different AWS Region than the source instance, due to the longer network channels between regional data centers.

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_ReadRepl.html#USER_ReadRepl.XRgn

Additionally, cross-region replicas for Aurora/Postgres are not yet available.

Cross-region replicas are only available for Aurora/MySQL... but a cross-region replica is not for zero downtime or failover, anyway -- it's only for geo/latency-based read scale-out or disaster recovery, because once you promote the replica, the original master has to be abandoned, because replication is one-way.

If, when you said "region," you were actually referring to availability zones, then that is much more straightforward, since the backing store of Aurora instances is replicated across 3 availability zones within the region, and replication is synchronous. All replicas in a single region can be synchronous, even in different AZs, since they all share the same replicated storage.