Amazon Aurora is an AWS-optimized relational database engine that supports running either MySQL or PostgreSQL databases. The service is drop-in compatible with MySQL 5.6 and later, and provides a migration tool that is able to assess and migrate a PostgreSQL database into the Aurora environment.
Amazon Aurora enables very simple management of the database while delivering high availability and high performance. The design behind an Aurora cluster differs slightly from the way the open source databases are delivered. With the open source databases, the Master database can have a synchronous slave replica within another availability zone, and then on top of those, we can deliver asynchronous read replicas that can be used to offload the read requests to the database.
An Aurora cluster is designed to always have one master instance, the so-called primary instance, and then multiple replica instances. Both the primary and the replicas have access to the same synchronously replicated backend storage volume. The instances themselves are stateless and are designed to only provide the database service and respond to database queries. The primary instance allows write access to the cluster volume while the replicas allow only for reads. To deliver high availability, the storage and the replicas are distributed across two or more availability zones. If the primary instance becomes unreliable or unavailable, Amazon Aurora will instantly promote one of the replicas to the primary role and deliver instant fail-over of all write traffic to that instance.
In essence, the design of Amazon Aurora enables us to have all nodes in the cluster take some work from the clients and, by having synchronous read replicas within one region, there is no lag in data being delivered out of the database which can be caused by asynchronous replication. The cluster can scale quite a bit since it supports delivering up to 15 replicas in addition to the primary instance, and also allows us to create global database clusters that can have an additional 16 replica instances deployed in other regions.
One feature of Amazon Aurora that is highly anticipated by some is the ability to provide multi-master clusters within our environment. At the time of writing, a preview program for the feature is available and you can sign up for the preview by following the link provided in the Further reading section of this chapter.