How to get the AWS RDS maximum connections from the AWS API? - amazon-web-services

Question

Is there a way to get the maximum number of connections for an RDS database from the AWS API?
I know that you can get the current number of connections from the DatabaseConnections Cloudwatch metric, but I'm looking to get the maximum/limit of connections possible for the database.
I also know that you can get it from within the database. For example, in Postgres, you can run:
postgres=> show max_connections;
However, I would like to get the value from outside the database.
I read in this this documentation about the max_connections DB instance parameter.
In most cases, the max_connections instance parameter is a value like this LEAST({DBInstanceClassMemory/9531392},5000) which depends on the DBInstanceClassMemory formula variable.
I read in this documentation that DBInstanceClassMemory can depend on several factors and is lower than the memory figures shown in the instance class tables.
Is there a way to get the DBInstanceClassMemory value from the API?
It looks like the AWS Console is able to get the value from outside of the database. See the red line in the graph below:
Edit: I found the JavaScript function that calculates the maximum number of connections in the AWS Console. It's called getEstimatedDefaultMaxConnections and it basically just divides the instance class' memory (from the instance class table) by the default memory-per-maximum-connections value (i.e. the default formula listed in the documentation). So, it ignores the fact that DBInstanceClassMemory will be less than the instance class' memory and it also ignores any changes you make to the max_connections DB instance parameter.
Is there a way for me to get that value using the API or to calculate it based on the DBInstanceClassMemory value (if it is available via the API)?

Answer 1

I ended up calculating an estimate of the number of maximum connections by fetching the max_connections DB parameter of the database, parsing it and evaluating it.
To get an estimate of the DBInstanceClassMemory value, I first fetched all of the available instance types using describe-instance-types and saved it to a file. I set DBInstanceClassMemory to 90% of this value to account for the memory lost to OS and RDS processes.
Then I:
Iterated through all of my RDS instances using DescribeDBInstances,
Fetched the DB parameters for each database using DescribeDBParameters and filtered for the max_connections parameter.
Parsed the max_connections parameter and evaluated the function using my estimated DBInstanceClassMemory for the database.