Scaling Mastodon

My instance mastodon.social has recently surpassed 43,000 users. I have closed registrations both to have more time to investigate the infrastructure and ensure a good experience for existing users, and to encourage more decentralization in the network (with a wonderful effect — the Mastodon fediverse now hosts over 161,000 people spread out over more than 500 independent instances!) But providing a smooth and swift service to 43,000 users takes some doing, and as some of the other instances are approaching large sizes themselves, it is a good time to share the tips & tricks I learned from doing it.