RDS Read Replicas are the replication of the primary database that allows applications to read data from this or these replicas.
Up to 15 Read replicas
Within AZ, cross AZ or cross-region
Replication is ASYNC so reads are eventually consistent
Applications must update the connection string to leverage read replicas.
It is useful if some new applications want to read the same data e.g. reporting apps. In this scenario, instead of making a bottleneck on the primary database, we may create new replicas and give the other apps to consume data from replicas so the production app will be unaffected.
It is only useful for SELECT queries
Network Costs
If async replication is on the same region but different AZs it FREE
If replication is cross-regions it causes EXTRA COST
