containerized nginx log rotation with logrotate

Question

Nginx doesn't have native log rotation, so an external tool, such as logrotate, is required. Nginx presents a challenge in that the logs have to be reopened post rotation. You can send a USR1 signal to it if the pid is available in /var/run.

But when running in a docker container, the pid file is missing in /var/run (and the pid actually belongs to the host, since it is technically a host process).

If you don't reopen the logs, nginx doesn't log anything at all, though it continues to function otherwise as web server, reverse proxy, etc.

Answer 1

You can get the process id from the Pid attribute using docker inspect and use kill -USR1 {pid} to have nginx reopen the logs.

Here's the /etc/logrotate.d/nginx file I created:

/var/log/nginx/access.log
{
    size 2M
    rotate 10
    missingok
    notifempty
    compress
    delaycompress
    postrotate
        docker inspect -f '{{ .State.Pid }}' nginx | xargs kill -USR1
    endscript
}