Extensions, logs, and the embedded database are by default stored in $CATTLE_HOME. Also, $CATTLE_HOME/etc/cattle is automatically added to the classpath, so $CATTLE_HOME/etc/cattle/cattle.properties will be found as the cattle config file and read.
If you are running the cattle.jar manually from the command line, $CATTLE_HOME defaults to $HOME/.cattle.
If you are running Cattle from the docker image “cattle/server,” the $CATTLE_HOME is by default /var/lib/cattle. If you want to customize Cattle while running docker you have two options (and plenty more you could think of).
Build a custom image: You can always build a custom image that packages your contents of $CATTLE_HOME, for example:
FROM cattle/server
ADD cattle-home /var/lib/cattle
Map a local folder to /var/lib/cattle: You can also just map a local folder to /var/lib/cattle, for example: docker run -v $(pwd)/cattle-home:/var/lib/cattle cattle/server