Aurora PostgreSQL Writer and Reader Region & AZ both shows as being at ap-southeast-2b. Is this an issue that has to be corrected?

Having both the Writer and Reader instances of an Aurora PostgreSQL cluster in the same Availability Zone (AZ) is not ideal for high availability and fault tolerance. This configuration does not provide the benefits of Multi-AZ deployment, which is designed to improve database availability.

In a typical Multi-AZ setup for Aurora, the Writer and Reader instances should be in different AZs within the same region. This arrangement helps ensure that your database remains accessible even if one AZ experiences an outage.

To address this issue, you can take the following steps:

1. Add a new Reader instance to your Aurora cluster. When you do this, Aurora should automatically place it in a different AZ from your existing instances.

2. Once the new Reader is fully operational and in sync with the Writer, you can initiate a failover to promote this new Reader to become the Writer. This will effectively move your Writer instance to a different AZ.

3. After the failover is complete, you can delete the original Reader instance that was in the same AZ as the old Writer.

This process will result in your Writer and Reader instances being in different AZs, improving the fault tolerance of your Aurora cluster. It's important to note that while you're making these changes, there may be a brief period of downtime during the failover process.

For future reference, when creating a new Aurora cluster or adding instances, Aurora typically tries to distribute instances across different AZs automatically to enhance availability. If you're consistently seeing instances being created in the same AZ, it might be worth checking your subnet group configuration to ensure it includes subnets from multiple AZs.

Remember to monitor your cluster's performance and availability during and after these changes to ensure everything is functioning as expected.
Sources
Can I fail over a writer instance to a new and scaled up reader instance in an Single-AZ Aurora cluster? | AWS re:Post
Move an Amazon RDS instance to a different Availability Zone | AWS re:Post
High availability for Amazon Aurora - Amazon Aurora