Guilherme Sehn

Full stack developer

How to update timezone information (zoneinfo) on Dokku

Recently, the Brazilian government abolished the daylight saving time where the timezone offset went from -3 to -2.

In cases like this, an outdated zoneinfo Linux file can cause your application to display times in DST when it shouldn’t. Ruby on Rails, for instance, uses the tzinfo gem, which reads Linux’s zoneinfo to gather timezone information including DST intervals.

When using Dokku with buildpacks, just rebuilding your application won’t work to get the zoneinfo updated, as the base Linux container image (gliderlabs/herokuish) will be cached by Docker. So in order for it to update the zoneinfo, first you need to clear Docker’s cache.

The commands are:

  1. docker system prune -a to clear the cached image
  2. dokku ps:rebuild [app-name] to rebuild your app using the new image. The build will take longer than usual since it needs to redownload the base image.