Yeah unfortunately it looks to be an EBS problem and if your underlying EBS volume housing your primary DB instance takes a dump then that is unfortunately going to cause replication to fall over too
Multi-AZ RDS deployment is supposed to protect you from that though. That's why it's 2x the price. We should have failed over to a different AZ w/o EBS issues.
If your source EBS volume is horked then you aren't going to be replicating any data to your backup host while the EBS volume is messed up (since your source data is unavailable). EBS volumes also don't cross/failover between AZ boundaries.
Maybe there was something bad with your replication server before the outage? It's hard to guess without knowing exactly what was happening at the time...
The whole point is to protect you from problems in one AZ by keeping a hot standby in another AZ. It doesn't matter whether it's due to EBS, power, etc. This is one of the primary reason to use RDS instead of running MySQL yourself on an instance.
Yes...what also sounds plausible is that since this was an EBS outage that the underlying EBS volume wasn't detected as being unavailable (if it in fact did become unavilable) so no failover to your other RDS server was initiated.
