Read replicas

Read replicas are copies of the database that serve reads, so a read-heavy app can add read capacity while every write still goes to one primary.

Use when

Read-heavy workloads with a modest write rate

Avoid when

Write-heavy load — every write still lands on the primary · Reads that must see the write that just happened

Trade-offs

Replication lag vs freshness — a replica can return an older answer than the primary · Read capacity only — writes still all land on the primary

Requires

Split app and database tiers, Load balancer