Container logs

Whatever the main process writes to stdout and stderr becomes the container's log. docker logs is the first thing to read when a container misbehaves.

How it works

docker logs api prints the log, --tail 50 the last lines, -f follows it live and --since 10m filters by time. Logs survive a stop but not docker rm. With Compose, docker compose logs shows every service, each line prefixed by its name.

What breaks

An app that writes to a file inside the container hides its errors from docker logs and fills its writable layer: log to stdout. And the default json-file driver keeps everything; without max-size, a chatty container can fill the disk.

In a terminal

docker logs --tail 50 api
docker logs -f --since 10m api

See it break, then fix it

Write the Dockerfile or the compose file, type the docker commands, and watch a simulated server run them through reboots, upgrades and traffic. Free to start.

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