Hello, In the documentation it says that the latency between different AZ is 1 to 2 milliseconds
https://docs.aws.amazon.com/sap/latest/general/arch-guide-architecture-guidelines-and-decisions.html (See Latency across Availability Zones)
There's a caveat. If you're only using the low-end instances like t2, you will likely have a lot of jitter and can sometimes encounter more latency.
If the instances are ENA (or SR-IOV) compatible, and using it, you'll get a big reduction in actual jitter and can realistically expect very low latency so long as you stay within the same VPC and region.
RDS specifically seems to be well optimized for networking, in the few years I've been using it (us-west-2) I've never had a single problem related to latency with the RDS instances themselves, but this is a N=1 data point.
Also, If you're using many instances connecting to one postgres server, make sure you're using pgbouncer or a similar connection pooler or you'll hit connection issues way before even a few ms of latency will cause problems.
Reserved Instances for RDS AuroraAccepted Answerasked 2 years ago
AWS RDS Aurora latency baselineasked 10 months ago
Latency issue between RDS and Lamdaasked a month ago
EC2 Dashboard says I have NO INSTANCESasked 2 years ago
RDS Postgresql migrate to Aurora Postgresql. Not showing "Aurora read replica" & "Migrate snapshot" options.Accepted Answerasked 9 months ago
How to ensure replica is in sync between AWS RDS PSQL primary DB and Aurora RDS PSQL replica cluster?asked 4 months ago
400 ms difference between APIG latency and Lambda LatencyAccepted Answerasked 2 years ago
Optimizing latency between application server (EC2) and RDSasked 9 months ago
Migration from Aurora PostgreSQL back to regular RDSAccepted Answerasked 4 years ago
Rds cross region latency issueasked 4 months ago