In another video we laid out seven critical metrics you should monitor with AWS CloudWatch to know when to scale your database cluster. This video will focus on the first of those metrics, database connections.

Amazon RDS databases have limits on the number of active connections they will allow. It isn't reported by CloudWatch and there's no visual indication on any graph. These connections will come from your application, cron jobs, or database admins. When the maximum number of connections has been reached all new connection requests are rejected. You'll be able to see the database connections in CloudWatch, but there is no indication of any limitations on the metric. One way to keep up with the limitation is by setting a CloudWatch alarm. You will need to remember to add this alarm to every server. Also, if you ever change the size of your servers, override the parameter groups to allow more connections, or change the size of your servers you'll need to change the alarms.

A better way to keep up with the limitation is to use Blue Matador. It will manage these types of thresholds for you all with a very quick setup.