RDS Cross Region Read Replica Not Successfully Creating

Do you have any BLOB data in your MYSQL? If So, make sure your parameter group has the maximum packet size set the same as your Master RDS instance.

I understand you're having trouble creating a functional cross-region read replica for your MySQL RDS cluster. This is a frustrating situation, especially when you're trying to scale your API into other regions. Let's explore some potential causes and solutions for this issue.

1. Binary logging: Ensure that binary logging is enabled on your source DB cluster. For cross-region read replicas to work, you need to set the binlog_format parameter in your DB cluster parameter group. Valid options are MIXED, ROW, or STATEMENT. After changing this parameter, you'll need to reboot the Aurora DB cluster for the change to take effect.

2. Replication lag: Cross-region replication typically experiences more lag time due to the longer network channels between AWS Regions. This increased lag could potentially cause connection issues. Monitor the ReplicaLag metric to see if it's unusually high.

3. Network connectivity: Verify that the security groups, network ACLs, and VPC configurations in both regions allow proper communication between the source and replica instances.

4. Parameter group settings: Ensure that the parameter groups in both regions are compatible. Pay special attention to parameters like max_allowed_packet. If this value is smaller on the replica than on the source, it can cause replication errors.

5. Storage and compute resources: Make sure your read replica has sufficient compute and storage resources, ideally matching those of the source DB cluster. Inadequate resources can lead to replication issues.

6. Upgrade requirements: In some cases, cross-region replication may require a database engine upgrade. If this is the case, you'll need to upgrade the engine version for all instances in the source DB cluster before creating the cross-region read replica.

7. Read-only setting: After creating the read replica, check that the read_only parameter is set to 1. Writing to tables on a read replica can break replication.

If none of these solutions resolve the issue, you may need to delete the problematic read replica and create a new one. When recreating, use the same DB instance identifier to maintain the same endpoint as the old read replica.

Remember, troubleshooting replication issues can be complex. If you continue to experience problems, don't hesitate to contact AWS Support for more personalized assistance.
Sources
Troubleshooting cross-Region replicas for Amazon Aurora MySQL - Amazon Aurora
Troubleshooting a MySQL read replica problem - Amazon Relational Database Service
Troubleshooting for Amazon RDS - Amazon Relational Database Service
Replicating Amazon Aurora MySQL DB clusters across AWS Regions - Amazon Aurora