Preface I want to write a universal shell-script which will add a proper IP address of docker host machine to /etc/hosts inside of container. You will probably advice me to put the service I want to access in another docker container too but for fastest tests on CI I want to access docker host machine by ip from container, that's why I need it. There was an where people were asking to make unified way to access host ip. There is no common solution for all platforms atm. People make scripts like this: grep dockerhost /etc/hosts echo $(ip r grep ^default cut -d' ' -f3) dockerhost >> /etc/hosts In order to access docker host machine I would like to use the same approach but it does not work for Mac atm. The result returned by: ip r grep ^default cut -d' ' -f3 will give a wrong answer 172.17.0.1 if Docker host machine is Mac (You won't be able actually to access your Mac from container with 172.17.0.1). That's why there is a feature in Docker for Mac - docker.for.mac.localhost with which you can access your host Mac from container. Word for mac text to speech.

At the moment it's not easy in Docker for Mac to connect to the internal IP addresses used by containers, because they're exposed in a tiny VM rather than on the host. Ideally specific ports should be published with docker run -p which sets up a tunnel from the Mac to the VM.

The problem I would like to write a universal shell script which will first try to resolve docker.for.mac.localhost and add the resolved address to /etc/hosts. If not (which means docker host is either windows or linux, not Mac), use the ip r grep ^default cut -d' ' -f3 approach and add to /etc/hosts too. The question is: How can I try to resolve docker.for.mac.localhost in ANY container? (some distros do not have nslookup for example).

Or maybe I should not try to resolve and I can just try to read docker.for.mac.localhost value from somewhere? My current thoughts are to try to use getent ahosts docker.for.mac.localhost, then in case command does not exist I will try to use nslookup (i.e. Busybox image does not have getent command). Probably I am wrong trying to resolve docker.for.mac.localhost and it can be retrieved in easier way. Please share your thoughts.

The race to zero is a theme that is catching on with Docker Images. Developers are racing to create the thinest most usable image possible. But why, do you ask?

If you've used Docker for any period of time then you will quickly realize that you spend a lot of time downloading or distributing images. This is not necessarily a bad thing for some but for others that scale their infrastructure are required to store a copy of every image that's running on each Docker host. If you are running the Ubuntu base image then you will need to store the 188MB image on each host. However, if you have a scenario that scales your application to a new host then you will not want to wait for the download of 188MB to complete before your container starts. Developers are working in much the same way as a race car mechanic would.

The goal is to strip all the unnecessary weight off the race car leaving just the bare essentials. Same goes for our Docker images. Do we need every Linux commands, library, etc inside of our container to run a Hello World script? Probably not.