We are experiencing an issue that repeats sometimes but it affects to the end users, I hope you can help us.
In our company, we have the following configuration:
- Four Moodle 3.5.4 nodes with PHP 7.1 and Apache 2.4.
- One MariaDB 5.5.52 server.
- Operating system is Red Hat 7.3.
- Two Moodles
- One balancer that manage connections through the servers.
- Cron is run each five minutes among all nodes (I mean, first node runs at 00, 20, 40 each hour, second node at 05, 25, 45 each hour, and so on...)
Sometimes it happens that one node start to perform worse than the others, with the following symptoms:
- Sessions in MariaDB from this node slowly start to increase: they usually start appearing as "Sleep" and 0 seconds in this state but with time the start to increase the time Sleeping and also the amount of sessions.
- In the PHP node, http sessions start to increase also and consecuently, the load of the server.
Once this behaviour is noticed, performance through this node is worse than others, response time and even timeouts.
There is not apparent reason for this behaviour, these servers are dedicated to Moodle, there is not any error in /var/log/messages or any other log. Also, is not always the same node.
Has this happened to anyone before?
Thanks in advance.