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This page describes what to do in case of an Icinga alert. For more information you could search the govuk-puppet repo for the source of the alert
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Last updated: 17 Sep 2020

Established connections exceed

This alert triggers when the number of established connections to a port exceeds a certain number. This can be configured for specific applications, but the default relates to the number of Unicorn worker processes if this is configured, or 2 if it’s not. This is because Unicorn can only handle as many concurrent connections as it has workers.

If this alert is firing, it can suggest that requests are coming in to the application faster than it can handle, and they’re beginning to back up. This is bad, as it means that the requests will be slower, as the application wasn’t able to start processing it immediately.

If you’re seeing this alert regularly for an app and the machine it’s on has enough memory to cope with more workers then you can increase this amount via puppet. An example of increasing the unicorn workers for an app can be found here.