Hi!
Yes, dockerfile is available same as the rest of the code. You can find it here. You can see that docker build is multi-staged. We build WAR file in first stage and use that in the images we publish. Jenkins builds images every 20 minutes if any changes were made for versions starting from 2.30.
Thanks for sharing, great to hear about your positive experience dockerising DHIS2 instance! If you get to try our images, please do not hesitate to give feedback or request features