RDS read Replicas

[ishan-sharma]

In the RDS cheatsheet, it is mentioned that the Database instance is copied asynchronously to read replicas. What does asynchronously copy mean here?

Does it mean that when traffic is less on the Database instance only then the read replica is copied or due so some other reasons?

[Jon-Bonso]

Hi Ishan,

For Read Replicas, the database updates on the source DB instance will be replicated using a supported engine’s native, asynchronous replication. You can create multiple read replicas for a given source DB Instance and distribute your application’s read traffic amongst them.

Asynchronous replication is simply a one-way data synchronization in which one server acts as the master, while one or more other servers act as slaves. The master here is the source DB instance and the slaves are the Read Replicas. Any changes made in the source DB (master) will be pushed to the read replica (slave), but since the read replica is read-only, there’s no way that a change in the replica will be pushed to the master.

In contrast, synchronous replication is a two-way synchronization. This is the case for Multi-AZ deployments. Updates to your DB Instance are synchronously replicated across Availability Zones to the standby DB instances in order to keep both in sync and protect your latest database updates against DB instance failure.

Cheers,

Jon Bonso