AWS RDS: How to get hold of the Current Activity / Number of Connections?

Using the AWS RDS console it is very easy to see the number of connections to an instance in the "Current Activity" column:

How do I get this information from the aws cli? As far as I can tell, aws rds describe-db-instances does not seem to have this particular piece of information.

NOTE: For my purposes, it would be enough to know if there are any connections.

Solution

For metrics, you should be using the aws cloudwatch tool. To get the number of database connections currently, you could use something like this:

aws cloudwatch get-metric-statistics --namespace AWS/RDS
--metric-name DatabaseConnections --start-time 2018-06-14T16:00:00Z
--end-time 2018-06-14T16:01:00Z --period 60 --statistics "Maximum"
--dimensions Name=DBInstanceIdentifier,Value=your-db-identifier

You'll need to combine it with code or a script to insert the correct --start-time and --end-time values.