The neat way to re-run a layer daily is to use a build arg:

  FROM debian
  
  ARG APT_UPDATE_DATE
  RUN apt-get update && apt-get upgrade -y

Then `docker build --build-arg APT_UPDATE_DATE=$(date +%Y%m%d)` will always re-run the `apt-get update` for the first build each day. You probably also want `--pull`.