Multi AZ

We use this concept to handle disaster recovery to make our DB more high availability.

It will have another DB called standby DB that synchronized data frommaster DB so when the master DB is failed , It used standby DB to recovery process . (Read replica can be used as standby DB). Application used one DNS name to connect with DB so in case that master DB failed it will automatic failover to connect standby DB.

From Single AZ to Multi AZ (!Important)

It has zero down time operation to move DB from single AZ to multi AZ. Firstly It creates a snapshot for master DB next It restore DB in new AZ from snapshot and establish sync connection from master to this new DB.