Linode sent a high CPU warning about a month ago now (not something I've received before), but I don't recall noticing any issues - I assumed it either resolved itself and/or Matt restarted the server; since there haven't been any more warnings I assumed it was a one-off and nothing to worry about.

One possibility is aggressively crawling bots - in the past I've had issues with Semrush bot and a few others and blocked them - so maybe we need an updated robots.txt - it's a low-effort first step at least.