FediMeteo, timezones, and the art of not breaking what already works

I have already written about how FediMeteo was born, and about how HAProxy helps reduce the number of requests that reach snac. Seen from the outside, FediMeteo almost seems still. There is a static homepage, regenerated every hour. There are the city pages, with their forecasts. There are RSS feeds waiting to be fetched, JSON objects waiting to be requested, Fediverse instances refreshing data, subscribing, unsubscribing, retrieving profiles, and reading notes. That is the visible part. Behind it, however, FediMeteo is much more than a homepage, a few ActivityPub accounts, and a well-behaved reverse proxy. It is a chain of small pieces, in proper Unix style, each trying to do one thing and do it as well as possible. That chain, although almost invisible from the outside, was not born already tidy. It changed, was rewritten, adapted to new countries, timezones, ambiguous city names, external service limits, and also to my own mistakes. Some mistakes were small. Others were much less…