Log Rotation For Docker Containers

One of the twelve pillars of a well behaved application is "Logs". However, having an infinitely expanding file on your server isn't ideal. So let's rotate it.

Logging parameters.

Docker allows you to configure two parameters. max-size and max-file.

max-size specifies how big a single file can be. So one container can have a log size as big as X megabytes.

max-file is the maximum number of log files persisted at any given time.

To change these we simply have to create or edit a daemon settings file.

sudo vim /etc/docker/daemon.json

and update it's contents to match the following.

{
    "log-opts": {
        "max-size": "128m",
        "max-file": "128"
    }
}

The combination above allows for up to 128 128MB files at once for a total of 16.38400 gigabytes of used storage at max capacity.

For the change to take effect you'll also need to restart the daemon & all of your containers.

sudo service docker restart

Pro Tip: Use fluentd & splunk to transform and aggregate your logs to a centralized location.

Sources: 12 Factor Docker Documentation