AWS Redis cluster mode - what is the difference between Auto-failover and Multi-AZ flag?

Question

I couldn't find the answer anywhere, and the description field when hovering are identical for me:

"Status of Multi-AZ Automatic Failover. If enabled, in case of primary node loss, failover to a read replica will happen automatically"

"Status of Automatic Failover. If enabled, in case of primary node loss, failover to a read replica will happen automatically"

So does it matter to have Multi-AZ on or off? My guess is with Multi-AZ on, it would allow failing-over to read replicate from the other AZ.

Thank you

Commend

Answer 1

Both options require that the Number of Replicas field be > 0 since you can't have automatic failover if you don't have replicas to failover to.

Assuming it's >= 1, the only difference with the Multi-AZ flag is that without it, the replicas would all be in the same AZ, and if the entire AZ is down (opposed to just the primary Redis instance) the replicas would all be down too.

If using Multi-AZ, if the primary is down, it will failover to a replica on another AZ, greatly increasing the chance that the replica is up.

Orsini

You can still place ReadReplicas across multiple AZs with only Auto-Failover enabled, but I'm not sure about the value add. It seems that Auto-Failover by itself would only happen to a ReadReplica within the same AZ, even though you can failover to a ReadReplica in another AZ just fine manually. – Stand