I did SRE for years. A lot of time it would end up being DNS or routing somewhere outside of our control. Sometimes a disk would get close to filling up and a

I did SRE for years. A lot of time it would end up being DNS or routing somewhere outside of our control. Sometimes a disk would get close to filling up and a cron would clear it just in time so you would see decreasing performance then it would clear. Other times we would have a customer that did something that we just did not expect with the system and it would cause SQL queries to slow down in ways we could not imagine. And it was transient so those would be hard to find or explain. Or we would hit a limit in the load balancer (haproxy) in really odd ways. Too much traffic on the frontend or not enough capacity in the backend. And many other various ways of things not working. Haproxy was and still is amazing software. Really almost magical.