Metrics tell you that something is wrong. Traces tell you where. Logs tell you why. Use them in that order and each step narrows the search — start with logs and you are grepping a firehose. Here is what each one is actually for, and the field that connects all three.
The top search result tells you to run docker system prune -a --volumes. It frees the space and deletes your database. Here is how to measure Docker disk usage properly, reclaim it from safest to most destructive, and fix the logs that Docker never reports on.
Two static binaries, a package and four systemd units. How to install Prometheus and Grafana on a single server from scratch, wire in node_exporter, put nginx and TLS in front, and keep the ports that have no authentication off the public internet.
Almost every TLS certificate error traces back to one of three causes: a broken chain, a hostname the certificate does not cover, or an expiry nobody was watching. Here is how to tell them apart in under a minute, and how to stop the third one from ever happening again.
Most "the site is down" tickets are really DNS problems wearing a costume. Here's the practical DNS troubleshooting workflow I use — how to read dig output, follow the delegation chain, decode SERVFAIL and NXDOMAIN, and stop blaming propagation for things that are actually caching, TTL, or DNSSEC failures.