EFS Client Connections Metric Fluctuations

Question

Hello,

I have 3 EC2 instances, each mounted to the same EFS file system. For the file system metric "Client connections", I would expect to have a constant value of 3.

However, when viewing this graphed metric on the "Sum" statistic, there are periodic fluctuations. Most of the time the value is 3, but sometimes can drop to 2, then sometimes go up to 4.

Please help me understand why this is happening. I followed the documentation for mounting but perhaps something went wrong somehow? I'm concerned there is some intermittent connection issue that may impact performance/reliability.

Any suggestions on how I should further troubleshoot?

Thanks for reading.

Answer

Metrics are a "point in time" measurement. The number you're seeing is true for an instant - when the measurement is taken.

My guess here (and it is a guess) is that there are times when one of your instances has disconnected (there will be timeouts, reboots, kernel updates, many things that can cause a brief disconnect) and during that time there will be one less connection to EFS; and that may be when the metric is calculated.

Similarly, an unexpected drop in a connection and a subsequent reconnection will see a situation where EFS thinks the old connection is still alive (it will timeout eventually) as well as the new connection. In that case you'll see four connections for a short period.

However: It's impossible to tell without detailed logs from the operating system and similarly detailed logs from EFS. Our support team can assist with troubleshooting the EFS side so I'd recommend that you raise a support case with them to dive deeper.

From a reliability and performance perspective I would enable detailed filesystem and network logging on your instances (temporarily) to try and determine if and why connections are dropping.

EFS Client Connections Metric Fluctuations

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