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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: 22 Aug 2022

mongod replication lag

Investigating the problem

Begin by checking the Mongo cluster status, then checking the replication info

Possible fixes

Try restarting one of the lagging mongodb secondaries.

SSH into a non-primary machine and run:

sudo service mongodb restart

This may restart replication on that node, and also cause the other lagging node to resync with the primary node and restart its own replication.

If you need to restart mongodb on the other secondaries, do this one node at a time, as load on the primary mongo node may be increased by the replication.

If restarting doesn’t solve the problem, you can force a resync.