Log rotation

Docker keeps everything a container prints, by default in a json-file that only disappears with the container. Rotation caps it: max-size and max-file, per container or for the whole daemon.

How it works

logging: options: max-size: "50m", max-file: "3" keeps at most three files of 50 MB and deletes the oldest. The local driver rotates and compresses by default (100 MB). log-opts in /etc/docker/daemon.json sets a default for every new container. New options only apply to containers created afterwards.

What breaks

One chatty container (debug logs left on, an error in a loop) fills the disk in hours; then the database cannot write, builds fail and other containers crash. docker system df does not count these files. driver: none saves the disk but leaves nothing to read when something goes wrong.

In compose.yaml

x-logging: &logging
  driver: json-file
  options:
    max-size: "50m"
    max-file: "3"

services:
  api:
    image: shop-api:4.2
    logging: *logging

See it break, then fix it

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