Outputting to the console, in Docker, from a cron job

If you’re googling this exact title, you’re probably bumping your head against the same things I was today. I was debugging a completely different project, and needed to print to the console, from a cron job, in a Docker container. Turns out this isn’t as straightforward as I thought.

Foreground cron

Before you even get to the problem space, here’s a tip. If you want to have a cron job running in a container, start cron in the foreground. If you do not, Docker realises nothing is going on, and exits. If you want to keep the container active so your cron jobs get a chance to execute, then start it in the foreground.