How to update /etc/hosts file in Docker image during "docker build" - docker

Question

I want to update my /etc/hosts file during "docker build".
I added below line in Dockerfile but it's neither updating /etc/hosts file nor giving any error.
RUN echo "192.168.33.11 mynginx" >> /etc/hosts
I need to update /etc/hosts. Can anyone suggest on this?

Answer 1

With a more recent version of docker, this could be done with docker-compose and its extra_hosts directive
Add hostname mappings.
Use the same values as the docker run client --add-host parameter (which should already be available for docker 1.8).
extra_hosts:
- "somehost:162.242.195.82"
- "otherhost:50.31.209.229"
In short: modify /etc/hosts of your container when running it, instead of when building it.
With Docker 17.x+, you have a docker build --add-host mentioned below, but, as commented in issue 34078 and in this answer:
The --add-host feature during build is designed to allow overriding a host during build, but not to persist that configuration in the image.
The solutions mentioned do refer the docker-compose I was suggesting above:
Run an internal DNS; you can set the default DNS server to use in the daemon; that way every container started will automatically use the configured DNS by default
Use docker compose and provide a docker-compose.yml to your developers.
The docker compose file allows you to specify all the options that should be used when starting a container, so developers could just docker compose up to start the container with all the options they need to set.

Answer 2

You can not modify the host file in the image using echo in RUN step because docker daemon will maintain the file(/etc/hosts) and its content(hosts entry) when you start a container from the image.
However following can be used to achieve the same:
ENTRYPOINT ["/bin/sh", "-c" , "echo 192.168.254.10 database-server >> /etc/hosts && echo 192.168.239.62 redis-ms-server >> /etc/hosts && exec java -jar ./botblocker.jar " ]
Key to notice here is the use of exec command as docker documentation suggests. Use of exec will make the java command as PID 1 for the container. Docker interrupts will only respond to that.
See https://docs.docker.com/engine/reference/builder/#entrypoint

Answer 3

I think docker recently added the --add-host flag to docker build which is really great.
[Edit]
So this feature was updated on 17.04.0-ce
For more detail on how to use docker build with the --add-host flag please visit: https://docs.docker.com/edge/engine/reference/commandline/build/

Answer 4

Since this still comes up as a first answer in Google I'll contribute possible solution.
Command taken from here suprisingly worked for me (Docker 1.13.1, Ubuntu 16.04) :
docker exec -u 0 <container-name> /bin/sh -c "echo '<ip> <name>' >> /etc/hosts"

Answer 5

You can do with the following command at the time of running docker
docker run [OPTIONS] --add-host example.com:127.0.0.1 <your-image-name>:<your tag>
Here I am mapping example.com to localhost 127.0.0.1 and its working.

Answer 6

If this is useful for anyone, the HOSTALIASES env variable worked for me:
echo "fakehost realhost" > /etc/host.aliases
export HOSTALIASES=/etc/host.aliases

Answer 7

You can use the --add-host option during docker run.
For your case use:
docker run --add-host mynginx:192.168.33.11 [image_name]:[tag]
This will update your /etc/hosts
you can check it by using following commands:
docker exec -it [container_id] sh
if sh doesnt work for you ,then you can try bash or /bin/sh or /bin/bash
cat /etc/hosts

Answer 8

I just created a sh script and run it on start docker.
In this script I start all the services and update the hosts file:
on Dockerfile:
CMD /tmp/init_commands.sh & sleep infinity
init_comands.sh
any other commands...
echo "192.168.11.5 XXXXXXX" >> /etc/hosts
echo "192.168.11.6 XXXXXXY" >> /etc/hosts
echo "192.168.11.7 XXXXXXZ" >> /etc/hosts

Answer 9

Following worked for me by mounting the file during docker run instead of docker build
docker service create --name <name> --mount type=bind,source=/etc/hosts,dst=/etc/hosts <image>

Answer 10

Tis is me Dockefile
FROM XXXXX
ENV DNS_1="10.0.0.1 TEST1.COM"
ENV DNS_1="10.0.0.1 TEST2.COM"
CMD ["bash","change_hosts.sh"]`
#cat change_hosts.sh
su - root -c "env | grep DNS | akw -F "=" '{print $2}' >> /etc/hosts"
info
user must su

Answer 11

Just a quick answer to run your container using:
docker exec -it <container name> /bin/bash
once the container is open:
cd ..
then
`cd etc`
and then you can
cat hosts
or:
apt-get update
apt-get vim
or any editor you like and open it in vim, here you can modify say your startup ip to 0.0.0.0