Docker compose should not mount /app from working directory

[icarito]

Only when the app really needs to write to a directory it is okay to mount the directory as a volume. Otherwise it's wise to let the app use the build-time files that are already at the container , providing further isolation and reliability.

The questions is what directory / directories are needed to be written at runtime?
#4858 is a start to this.

I'm thinking also the log directory needs to be writable?