Aurora stores copies of the data in a DB cluster across multiple Availability Zones in a single AWS Region. Aurora stores these copies regardless of whether the instances in the DB cluster span multiple Availability Zones.
When data is written to the primary DB instance, Aurora synchronously replicates the data across Availability Zones to six storage nodes associated with your cluster volume. Doing so provides data redundancy, eliminates I/O freezes, and minimizes latency spikes during system backups. Running a DB instance with high availability can enhance availability during planned system maintenance, and help protect your databases against failure and Availability Zone disruption.
Note the a single AZ solution will go down if the AZ goes down however the data is available in other AZs so a new instance can be launched in the other AZ but no automatically unless you have a replica in that AZ
For a cluster using single-master replication, after you create the primary instance, you can create up to 15 read-only Aurora Replicas.
During day-to-day operations, you can offload some of the work for read-intensive applications by using the reader instances to process
SELECT queries. When a problem affects the primary instance, one of these reader instances takes over as the primary instance. This mechanism is known as failover. Many Aurora features apply to the failover mechanism.
To use a connection string that stays the same even when a failover promotes a new primary instance, you connect to the cluster endpoint. The cluster endpoint always represents the current primary instance in the cluster.
Within each AWS Region, Availability Zones represent locations that are distinct from each other to provide isolation in case of outages. We recommend that you distribute the primary instance and reader instances in your DB cluster over multiple Availability Zones to improve the availability of your DB cluster. That way, an issue that affects an entire Availability Zone doesn’t cause an outage for your cluster.
For high availability across multiple AWS Regions, you can set up Aurora global databases. Each Aurora global database spans multiple AWS Regions, enabling low latency global reads and disaster recovery from outages across an AWS Region. Aurora automatically handles replicating all data and updates from the primary AWS Region to each of the secondary Regions