How can you make the Docker container use the host machine's '/etc/hosts' file?

Question

I want to make it so that the Docker container I spin up use the same /etc/hosts settings as on the host machine I run from. Is there a way to do this?

I

Answer 1

If trusted users start your containers, you could use a shell function to easily "copy" the /etc/hosts entries that you need:

add_host_opt() { awk "/\\<${1}\\>/ {print \"--add-host $1:\" \$1}" /etc/hosts; }

You can then do:

docker run $(add_host_opt host.name) ubuntu cat /etc/hosts

That way you do not have to hard-code the IP addresses.

Answer 2

Add a standard hosts file -

docker run -it ubuntu cat /etc/hosts

Add a mapping for server 'foo' -

docker run -it --add-host foo:10.0.0.3 ubuntu cat /etc/hosts

Add mappings for multiple servers

docker run -it --add-host foo:10.0.0.3 --add-host bar:10.7.3.21 ubuntu cat /etc/hosts

Reference - Docker Now Supports Adding Host Mappings

Answer 3

If you are using docker-compose.yml, the corresponding property is:

services:
  xxx:
    network_mode: "host"

Source

Answer 4

extra_hosts (in docker-compose.yml)

https://docs.docker.com/compose/compose-file/

Add hostname mappings. Use the same values as the docker client --add-host parameter.

extra_hosts:
 - "somehost:162.242.195.82"
 - "otherhost:50.31.209.229"

Answer 5

Add this to your run command:

-v /etc/hosts:/etc/hosts

Answer 6

Use --network=host in the docker run command. This tells Docker to make the container use the host's network stack. You can learn more here.