Chart Aurora Postgres read replica instance number?

There is no direct metric in AWS CloudWatch that allows you to monitor the number of read replica instances for an Aurora PostgreSQL database.

AWS CloudWatch primarily provides metrics for various system aspects such as CPU utilization, database connections, free storage space, etc., but doesn't provide a metric for the count of read replicas.

However, there are a couple of workarounds:

• AWS RDS API: You can use the AWS RDS API, specifically the describe-db-instances command, to get information about your DB instances. You can filter the results to return only instances that are read replicas by looking at the ReadReplicaSourceDBInstanceIdentifier attribute. A small script can be used to automate this process and you can push these metrics to CloudWatch custom metrics to track the number of read replicas over time.

• AWS Lambda: You can set up an AWS Lambda function to automatically call the RDS API at regular intervals. The function would count the number of read replicas and then publish that count as a custom metric to CloudWatch. This way, you could have a "chart" of the number of read replicas over time.

Remember, creating custom metrics in CloudWatch may incur additional costs, so keep that in mind when setting up your monitoring system.