Instances hang on reboot

Question

Suggestions on why this happens, and any way to avoid it:

Two (smallest) Lightsail instances, running Amazon Linux 2023 - latest release minus one.
One instance in UK region and one in France region.
Update to latest release. Reboot - fine.
A few minutes later, reboot again. Both hang in "Stopping" state.
Give up and force stop - both eventually stop.
Attempt to start - they come up, but can't connect (ssh) to them.
Try a reboot - reboot returns to Running within a second. (Didn't work).
Go through force stop/start again, still hangs.
Both are using ~50% cpu - these have NO applications installed or running - just wireguard.

Available CPU burst is, of course running down, and down ...

Give up and restore both from snapshots. Both run fine.

This is not the first time I have seen this sort of behavior - with different OS, so I believe it is a VM bug.

Answer

Check the instance metrics page for your instances and see if your software (wireguard) is remaining within the sustainable zone https://lightsail.aws.amazon.com/ls/docs/en_us/articles/amazon-lightsail-viewing-instance-burst-capacity

If your instance is consistently running above the sustainable zone you will exhaust your burst capacity. Larger instances have higher sustainable thresholds and a greater burst capacity.

Instances hang on reboot

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