Aggressive caching for a Mastodon reverse proxy: what to cache, what to never cache, and why content negotiation will eventually betray you (opens in new tab)

I have written before about putting a cache in front of . The general idea is always the same: the reverse proxy should absorb the repetitive, public work that has no business reaching the application server. This post is the same idea applied to a much louder neighbour: a Mastodon instance. The instance is Mastodon is heavier than snac in every direction. It has Puma and Sidekiq behind it, more endpoints, more streaming, more federation patterns, and one specific characteristic that complica...