This is an example of setting up a NAT inside docker - in a fairly self-explanatory and minimal way. There are three examples that you can run in this setup: a positive example, a negative example, and a chatty positive example for debugging and demonstration purposes.

tl;dr: bind the cron definition file as a volume, and wire running it, as part of the image (in your Dockerfile).

Here is frmo a Stackoverflow answer:

Let's say you have a file hello-cron:

I've used the following script to do this: