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arevur
arevur

Reputation: 743

Docker container doesn't expose ports when --net=host is mentioned in the docker run command

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.

Upvotes: 74

Views: 99905

Answers (6)

Mahdi mehrabi
Mahdi mehrabi

Reputation: 1744

My OS is Linux but for me, the problem was using the docker rootless.

and I believe Rootless Docker does not support the --network host mode the same way traditional Docker does. This is because rootless Docker uses user namespaces and other mechanisms that can affect networking capabilities.

Ports exposed by containers in rootless Docker might not be directly accessible from the host in the same way. This is due to the differences in how networking is handled.

so when you want to use --net=host or --network=host run your docker command with sudo or delete your rootless docker

systemctl stop docker.service
dockerd-rootless-setuptool.sh uninstall --force
systemctl start docker.service

and add your user to docker group

 sudo usermod -aG docker $USER
sudo chown root:docker /var/run/docker.sock
sudo chown -R root:docker /var/run/docker

now you have access to the docker command without sudo and you are able to use --network=host.

if you have any problem accessing Docker without sudo uninstall your Docker and install it again but this time make it rootless by adding it to the docker group.

Upvotes: 1

Shane Gannon
Shane Gannon

Reputation: 7738

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.

Updated 2024: As per comments and other answers there have been changes in this area. See Docker container doesn't expose ports when --net=host is mentioned in the docker run command

Upvotes: 179

Smart Manoj
Smart Manoj

Reputation: 5851

The host networking driver only works on Linux hosts, but is available as a Beta feature, on Docker Desktop version 4.29 and later. To enable this feature, navigate to the Features in Development tab in Settings, and then select Enable host networking.

Upvotes: 4

starguy
starguy

Reputation: 241

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

tells us:

"Host networking is also supported on Docker Desktop version 4.29 and later for Mac, Windows, and Linux as a beta feature. To enable this feature, navigate to the Features in development tab in Settings, and then select Enable host networking."

And it works for me.

Upvotes: 1

rjdkolb
rjdkolb

Reputation: 11888

On Linux, I have always used --net=host when myapp needed to connect to an another docker container hosting PostgreSQL.

myapp reads an environment variable DATABASE in this example

Like Shane mentions this does not work on MacOS or Windows...

docker run -d -p 127.0.0.1:5432:5432 postgres:latest

So my app can't connect to my other other docker container:

docker run -e DATABASE=127.0.0.1:5432 --net=host myapp

To work around this, you can use host.docker.internal instead of 127.0.0.1 to resolve your hosts IP address.

Therefore, this works

docker run -e DATABASE=host.docker.internal:5432 -d myapp

Hope this saves someone time!

Upvotes: 23

dnephin
dnephin

Reputation: 28150

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.

Upvotes: 36

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