Aurora Database Replicas

Correct Answer - B, D.

An Amazon Aurora DB cluster consists of primary DB instances and Aurora Replicas.

Check the details in.

Option A is incorrect: Because the replicas can only serve the read traffic.

Option B is CORRECT: Because the replicas spread in different availability zones to ensure that the database still works even if one availability zone has an outage.

Option C is incorrect: Because there is no such limitation, and each Aurora DB cluster can have up to 15 Aurora Replicas in addition to the primary DB instance.

Option D is CORRECT: This is a key feature of Aurora Replica.

Option E is incorrect: Because Aurora Replica is configured with the same storage volume as the primary DB instance, according to the above link.

Sure, I'd be happy to provide a detailed explanation of the correct statements regarding Aurora database replicas in the context of your question.

Firstly, statement B is correct. When you create an Aurora MySQL cluster, Aurora automatically creates up to 15 replicas in different Availability Zones within the same AWS Region as the primary database instance. This is done to ensure high availability and durability of your database by enabling automatic failover to a replica in case the primary instance becomes unavailable due to various reasons such as hardware or software failures, network issues, or scheduled maintenance. By having replicas in different AZs, the impact of any issues that might occur in one AZ is minimized.

Secondly, statement D is also correct. Aurora automatically performs failover to a replica if the primary instance becomes unavailable. This is done in seconds with no data loss. When a failover occurs, the replica is promoted to be the new primary instance and starts handling all traffic, while the failed primary instance is replaced with a new replica. The failover process is transparent to your application and Aurora ensures that the connection endpoints are updated automatically.

To further explain the other statements and why they are not correct:

A. The replicas can share both the read and write traffic - This statement is partially correct. Aurora supports read scaling by offloading read traffic to replicas, but only the primary instance can handle write traffic. This is done to ensure data consistency across all replicas. You can configure your application to use read replicas for read-intensive workloads, but any writes must be directed to the primary instance.

C. By default, there is only one replica generated in each availability zone - This statement is incorrect. As mentioned earlier, Aurora automatically creates up to 15 replicas in different AZs within the same AWS Region as the primary database instance. The exact number of replicas created depends on the cluster size and the amount of available resources in each AZ.

E. Replicas are configured with smaller storage volume than the primary DB instance to save cost - This statement is also incorrect. Aurora replicas have the same storage volume as the primary instance. The only difference is that replicas are read-only and can't handle write traffic. You can create Aurora replicas with different instance classes or sizes to better match your workload requirements, but the storage volume remains the same.

I hope this helps clarify the correct statements and provides a better understanding of Aurora database replicas in AWS.