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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
Last updated: 24 Mar 2021

Unicorn Herder

‘app unicornherder running’

This alert means the Unicorn Herder process has disappeared for the named app, so the app is still running but we don’t know about it and can’t control it.

To fix this, manually kill off the unicorn workers for the app and restart the herder process.

SSH into the affected machine and get the process ID of the unicorn master:

ps aux | grep "unicorn master" | grep "<app name>" | awk '{ print $2 }'

If there is no unicorn master process for the app, then it has crashed.

Kill the process:

kill -9 <pid>

Then start the app again:

sudo service <app-name> start