I think the philosophy for logs is that they are THE user interface for operators of your service. If you are SaaS, that's you! If you provide software for self-hosting, that's your customers. It can't be an afterthought; this is how ordinary people can peer deep into your system to understand what's wrong with it. If they figure it out, they don't page you. If it's useless, you can't fix it after they page you. Be paranoid and make your subsystems show their work. Anything you want to know while debugging, print it, don't make the user "hey just run this and tell me what it returns". I think there is an art here, and many treat it as an afterthought.

I always liked structured logs because it frees my mind from coming up with how I want to format arguments. "New HTTP request for /foobar from 1.2.3.4 with request-id ac31a9e0-5d57-44de-9e98-60fa94d3e866" is a pain to read and maintain. `log.Debug("incoming http request", logger.IP("remote-ip", req.Address), logger.String("request-id", req.ID), logger.String("route", req.Route))` is easy to write, and the resulting logs are easy to analyze!

I do like myself some pretty colorful logs, but prefer JSON as the intermediary. It's pretty easy to post-process the logs into something understandable. I wrote https://github.com/jrockway/json-logs for this task. Give it a stream of JSON logs, get colorful text out. Add/drop fields or select/highlight interesting lines with JQ or regular expressions (with -A -B -C of course). Installable on Linux or Mac with Homebrew ;) It's one of the few pieces of software I wrote for myself that passes the "toothbrush test". I use it twice a day every day. And that's a good day when I'm not pulling my hair out over an obscure issue ;)