This is another letter to future me.

In the future, if everything goes pear-shaped, and you decide its easier to burn this server to the ground and start anew using one of Digital Ocean's droplets and WordOps (a handy set of scripts and configs to get your LAMP/LEMP stack working in seconds), please remember this: delete the default regex lookups for atom, rss and json so they're not cached in your locations-wo.conf. If you don't, you won't have accessible feeds for as long as it takes you to remember this tip... Not that it's happened before.