Ssh from one container to another container

Question

I want to create a network of a container in which one central container should be able to ssh into all other containers. Through ssh central container can change a configuration of all other container using Ansible. I know that it’s not advised to ssh from one container to another, and we can use volume for data sharing but that doesn't fit to my use case. I am able to ssh from host to the container but I am not able to ssh from one container to another.

Docker file I am using is:

FROM ubuntu:16.04
RUN apt-get update
RUN apt-get install -y netcat ssh iputils-ping
EXPOSE 22

Image created by the Dockerfile is named ubuntu:v2

Then using below commands I created two containers u1 and u2

docker run -p 22 --rm -ti --name u1 ubuntu:v2 bash 
docker run -p 22 --rm -ti --name u2 ubuntu:v2 bash

In the container I am running below commands to create a user in container. Create user u1 in u1 container and u2 in u2 container

root@d0b0e44f7517:/# mkdir /var/run/sshd
root@d0b0e44f7517:/# chmod 0755 /var/run/sshd
root@d0b0e44f7517:/# /usr/sbin/sshd    
root@d0b0e44f7517:/#
root@d0b0e44f7517:/# useradd --create-home --shell /bin/bash --groups sudo u2  
root@d0b0e44f7517:/# passwd u2
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
root@d0b0e44f7517:/#
root@d0b0e44f7517:/#

I made two containers, both are same except one has user u1 and other has user u2 as shown above. After this, I tried to ssh from host to container using command ssh -X u2@localhost -p 32773 (32773 is a port which is mapped to container’s 22 port). So ssh works from host to container but I am not able to ssh from one container to another container.So can you help me to ssh from one container to other containers?

Answer 1

Use docker service discovery and then you can ssh from one container to another container. Here you can achieve service discovery by connecting all the containers to the same network.

docker network create -d bridge test
docker run -p 22 --rm -ti --name u1 --network test ubuntu:v2 bash 
docker run -p 22 --rm -ti --name u2 --network test ubuntu:v2 bash

Now from u1 you can ssh into u2 as ssh user@u2.

Answer 2

Login to docker conatiner

docker exec -it u1 /bin/bash
docker exec -it u2 /bin/bash

After logging in to conatiner run the below commands to install required tools for sshing

passwd          #Change the password of container it will be asked during ssh

apt-get update

apt-get install vim 

apt-get install openssh-client openssh-server

vi /etc/ssh/sshd_config 

Change the line "PermitRootLogin yes"

service ssh restart

Now you can ssh using root@container_ip to any container

Note: to get container ip you can run the below command

docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' <conatiner_name>