Docker container doesn't expose ports when --n

Question

I have a CentOS docker container on a CentOS docker host. When I use this command to run the docker image docker run -d --net=host -p 8777:8777 ceilometer:1.x the docker container get host's IP but doesn't have ports assigned to it.

If I run the same command without "--net=host" docker run -d -p 8777:8777 ceilometer:1.x docker exposes the ports but with a different IP. The docker version is 1.10.1. I want the docker container to have the same IP as the host with ports exposed. I also have mentioned in the Dockerfile the instruction EXPOSE 8777 but with no use when "--net=host" is mentioned in the docker run command.

Answer 1

I was confused by this answer. Apparently my docker image should be reachable on port 8080. But it wasn't. Then I read

https://docs.docker.com/network/host/

To quote

The host networking driver only works on Linux hosts, and is not supported on Docker for Mac, Docker for Windows, or Docker EE for Windows Server.

That's rather annoying as I'm on a Mac. The docker command should report an error rather than let me think it was meant to work.

Discussion on why it does not report an error

https://github.com/docker/for-mac/issues/2716

Not sure I'm convinced.

Answer 2

The docker version is 1.10.1. I want the docker container to have same ip as the host with ports exposed.

When you use --net=host it tells the container to use the hosts networking stack. So you can't expose ports to the host, because it is the host (as far as the network stack is concerned).

docker inspect might not show the expose ports, but if you have an application listening on a port, it will be available as if it were running on the host.