Replication with Amazon Aurora PostgreSQL
Following, you can find information about replication with Amazon Aurora PostgreSQL, including how to monitor replication.
Topics
Using Aurora Replicas
An Aurora Replica is an independent endpoint in an Aurora DB cluster, best used for scaling read operations and increasing availability. An Aurora DB cluster can include up to 15 Aurora Replicas located throughout the Availability Zones of the Aurora DB cluster's AWS Region.
The DB cluster volume is made up of multiple copies of the data for the DB cluster. However, the data in the cluster volume is represented as a single, logical volume to the primary writer DB instance and to Aurora Replicas in the DB cluster. For more information about Aurora Replicas, see Aurora Replicas.
Aurora Replicas work well for read scaling because they're fully dedicated to read operations on your cluster volume. The writer DB instance manages write operations. The cluster volume is shared among all instances in your Aurora PostgreSQL DB cluster. Thus, no extra work is needed to replicate a copy of the data for each Aurora Replica.
With Aurora PostgreSQL, when an Aurora Replica is deleted, its instance endpoint is removed immediately, and the Aurora Replica is removed from the reader endpoint. If there are statements running on the Aurora Replica that is being deleted, there is a three minute grace period. Existing statements can finish gracefully during the grace period. When the grace period ends, the Aurora Replica is shut down and deleted.
Aurora PostgreSQL DB clusters don't support Aurora Replicas in different AWS Regions, so you can't use Aurora Replicas for cross-Region replication.
Rebooting the writer DB instance of an Amazon Aurora DB cluster also automatically reboots the Aurora Replicas for that DB cluster. The automatic reboot re-establishes an entry point that guarantees read/write consistency across the DB cluster.
Monitoring Aurora PostgreSQL replication
Read scaling and high availability depend on minimal lag time. You can monitor how far
an Aurora Replica is lagging behind the writer DB instance of your Aurora PostgreSQL DB
cluster by monitoring the Amazon CloudWatch ReplicaLag metric. Because Aurora
Replicas read from the same cluster volume as the writer DB instance, the
ReplicaLag metric has a different meaning for an Aurora PostgreSQL DB
cluster. The ReplicaLag metric for an Aurora Replica indicates the lag for
the page cache of the Aurora Replica compared to that of the writer DB instance.
For more information on monitoring RDS instances and CloudWatch metrics, see Monitoring metrics in an Amazon Aurora cluster.
