🤔 Unexpected Aurora Cross-Region Read Replica Behavior - Need Expert Input

What you're experiencing is not the expected behavior for a standard Aurora MySQL cross-region read replica. Typically, Aurora read replicas should be read-only, not accepting writes.

The behavior you're describing suggests that what you have is not a standard read replica but potentially a split-brain scenario or an incorrectly configured replication setup. In a proper cross-region read replica configuration:

1. The replica should be read-only and should not accept writes (INSERT/UPDATE statements)
2. The replication flow should be one-way only (primary to replica)
3. Only the primary cluster should show IsClusterWriter: true

The fact that both clusters show IsClusterWriter: true is particularly concerning, as this indicates both clusters are operating as primaries. This could lead to data inconsistency issues since changes made in us-west-2 aren't propagating back to us-east-1.

For Aurora MySQL cross-region replication, the process works through binary log (binlog) replication where:

• Transactions committed on the primary cluster are recorded in binary log files
• These changes are sent through an I/O thread to relay logs in the secondary region
• The changes are then applied to the secondary Aurora cluster

Some potential causes for your situation:

• The replica might have been promoted to a writer at some point
• There might be configuration issues with the replication setup
• The binlog settings might be misconfigured

I recommend checking your binary logging configuration, verifying the replication status, and potentially recreating the cross-region replica if necessary to ensure proper read-only behavior.
Sources
Aurora MySql replication problem | AWS re:Post
Cross-Region Aurora Replicas - AWS Prescriptive Guidance

Can you please check if the DB cluster has write forwarding enabled? In the AWS Management Console, on the Configuration tab of the details page for the cluster, you see the status Enabled for Local read replica write forwarding. https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/aurora-mysql-write-forwarding.html

If its set to true that is most likely the cause of records getting accepted on the reader. https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/aurora-mysql-write-forwarding-enabling.html

Hi. No. Both clusters (primary and secondary) show:

Local read replica write forwarding Disabled

Local read replica write forwarding Disabled