AuroraBinLogReplicaLag reporting as -1

The AuroraBinLogReplicaLag reporting as -1 for the writer instance in your Aurora MySQL Cluster could indicate an issue with binary logging configuration or replication setup. Here are some steps you can take to address this:

1. Check if binary logging is enabled on your Aurora MySQL cluster. If it's not enabled, this could explain the -1 value for the writer instance. To enable binary logging, you'll need to modify the DB cluster's parameter group in the Amazon RDS console.

2. If binary logging is already enabled, you may need to reboot the writer instance for any recent changes to take effect. In Aurora MySQL version 2.09 and lower, rebooting the writer instance will also reboot all reader instances. For version 2.10 and higher, you'll need to manually reboot the reader instances as well.

3. Verify that the cluster parameter group associated with your Aurora MySQL cluster has the correct settings for GTID-based replication. If GTID-based replication is not needed, ensure that the 'gtid_mode' and 'enforce_gtid_consistency' parameters are set to 'OFF'.

4. If the issue persists after these steps, it's possible that there's an underlying problem with the replication process or the managed service itself. In this case, it would be advisable to contact AWS Support for further assistance, as they can investigate deeper into the managed service aspects that you don't have direct control over.

Remember that while Aurora is a managed service, there are still some configuration aspects that you can control. However, if the problem continues after trying these steps, engaging AWS Support would be the best course of action to resolve the issue with the AuroraBinLogReplicaLag metric.
Sources
Disabling GTID-based replication for an Aurora MySQL DB cluster - Amazon Aurora
Configuring Aurora MySQL binary logging - Amazon Aurora