This is more a bookmark than a post - but I’d like to write it down explicitly since everytime I need this I have to google it (and cutting through the false positivies sucks).
From 18.03 onwards our recommendation is to connect to the special DNS name
host.docker.internal, which resolves to the internal IP address used by the host.
This was taken from the docker-for-mac documentation were you can find more details.
Notice: This also works for locally mapped ports of other containerized services (and thus is handy for using containerized CLI tools with existing stacks).
Notice: This is not just a docker-for-mac thing but also works for docker-for-win