Mitigating Failures
When planning your MemoryDB for Redis implementation, you should plan so that failures have a minimal impact upon your application and data. The topics in this section cover approaches you can take to protect your application and data from failures.
Mitigating Failures: MemoryDB clusters
A MemoryDB cluster is comprised of a single primary node which your application can both read from and write to, and from 0 to 5 read-only replica nodes. However, we highly recommend to use at least 1 replica for high availability. Whenever data is written to the primary node it is persisted to the transaction log and asynchronously updated on the replica nodes.
When a read replica fails
MemoryDB detects the failed replica.
MemoryDB takes the failed node offline.
MemoryDB launches and provisions a replacement node in the same AZ.
The new node synchronizes with the transaction log.
During this time your application can continue reading and writing using the other nodes.
MemoryDB Multi-AZ
If Multi-AZ is activated on your MemoryDB clusters, a failed primary will be detected and replaced automatically.
MemoryDB detects the primary node failure.
MemoryDB fails over to a replica after ensuring it is consistent with the failed primary.
MemoryDB spins up a replica in the failed primary's AZ.
The new node syncs with the transaction log.
Failing over to a replica node is generally faster than creating and provisioning a new primary node. This means your application can resume writing to your primary node sooner.
For more information, see Minimizing downtime in MemoryDB with Multi-AZ.