I currently operate a Debian VPS with Linode to host a website. Yesterday, the entire VPS became unresponsive for about 40 minutes. Checking the graphs that Linode provides I see that the entire system seems to have ground to a halt during this time:
Checking dmesg
just yields a bunch of iptables denied
messages, but I suspect that these are as a result of the firewall operating correctly, since they're mostly obviously unreasonable (e.g. UDP packets, nonsense TCP packets, etc).
How would I go about diagnosing what happened, and take steps to prevent it from happening again?