Ssh from one containe to another container

Docker Engine General
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I want to create a network of a container in which one central container should be able to ssh into all other containers. I know that it’s not advised to ssh from one container to another, and we can use volume for data sharing but in my production network, there is a script which ssh into some system and does something. So I want to simulate the same environment using a container so that I can test new feathers and add in a production network.

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Hi :slight_smile:

So whats the question? :slight_smile:

Sure it can be done, by starting the sshd in the containers, is this purely ssh only containers or will the containers run some other service?

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Purely ssh only containers. @terpz Can you please help me to do it . I ran to containers with ssh running on both. I am able to ssh from host to both the container but I am not able to ssh from one container to another. I tried so many different ways but I failed :disappointed_relieved:.

  • 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

  • In the container I am running below commands
    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.

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I have also this problem. In our team we have few server and one central server which ssh into all other server and monitor them. So whenever I want to do some changes, I have to test in on production network which is dangerous. I want to make network of container and one of them ssh into all other container and monitor them or make changes using ansible. For that ssh is mandatory. So @terpz waiting for your answer :smiley:.

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I want to do something like this

Google Photos

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I will answer monday, im on a trip until then :slight_smile:

But there is many ssh-only containers on docker hub, or is your requirements different?

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I only want to ssh from one container to another and both the container should use Ubuntu base image. @tandeldipak had posted a dockerfile which build ubuntu image with has ssh & ip functionality can be consider to make container and that container should be able to ssh into one another. @terpz enjoy your trip :hotel: will discuss on monday.

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@terpz Please build an image from above docker file. It will be helpful for me as well as @uc123.

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Hi again.

Every container is isolated, so you need to join them somehow, the old way was to use links but now, the way would be to create a shared network between the containers.

With this Dockerfile:

FROM ubuntu:16.04
RUN apt-get update && \
apt-get install -y netcat ssh iputils-ping && \
mkdir /var/run/sshd && \
chmod 0755 /var/run/sshd && \
useradd -p $(openssl passwd -1 u2password) --create-home --shell /bin/bash --groups sudo u2

EXPOSE 22

CMD [“/usr/sbin/sshd”, “-D”]

And this docker-compose.yml:

You can run this command, if you have docker-compose installed, else: Overview of installing Docker Compose | Docker Docs

› docker-compose.exe up -d
Creating network “sshtest_sshtest” with the default driver
Creating sshtest_container1_1 …
Creating sshtest_container1_1 … done
Creating sshtest_container2_1 … done

then if you check your “docker ps” you will see that there is now 2 containers.
Connect to one of them and you should be able to ssh to container1/container2 with login (u2 / u2password)

3 Likes
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Hi @terpz I need a little help with alpine image. Are you familiar with that?

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depends on what you need help with?

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So, I made an alpine image with this Dockerfile …but when I create containers it always gives me sshd keys are missing and when I check sshd_config, it’s empty.
Dockerfile:
FROM alpine:latest

based on https://docs.docker.com/engine/examples/running_ssh_service/

RUN apk add --update ; apk add --no-cache
util-linux
iproute2
net-tools
iputils
iperf
tcptraceroute
openssh-server
RUN mkdir /var/run/sshd
RUN echo ‘root:doker’ | chpasswd
RUN sed -i ‘s/PermitRootLogin prohibit-password/PermitRootLogin yes/’ /etc/ssh/sshd_config
RUN echo ‘PermitRootLogin yes’ | cat >> /etc/ssh/sshd_config

SSH login fix. Otherwise user is kicked off after login

#RUN sed ‘s@session\srequired\spam_loginuid.so@session optional pam_loginuid.so@g’ -i /etc/pam.d/sshd
EXPOSE 22
CMD ["/usr/sbin/sshd", “-D”]

I have no idea where I am going wrong. If possible, please help.

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Hi @terpz
I’m having two application which are running on a separate docker containers.
Running OB-BAA (open source broadband forum project) in one container.
Running my application in another container. My usecase is to establish a ssh connection between my application and OB-BAA .I’m using libssh2 in my application for establishing a connection.
When I’m running my application from the host machine, i’m able to connect OB-BAA container.
But when i tried to run my application in a separate centos docker container ,
while establishing a connection libssh2_session_handshake got failed with error code as -8(LIBSSH2_ERROR_KEY_EXCHANGE_FAILURE).
I’m not sure why key exchange got failed when running inside a docker.
I tried the following ways

  1. generate the ssh-key again by ssh-keygen.
    2.copied the /root/.ssh folder from my linux machine to docker.
    3.Sharing the ssh-agent between host machine and docker by adding the below in docker-compose file

    environment:

    • SSH_AUTH_SOCK=/ssh-agent
      volumes:
    • ${SSH_AUTH_SOCK}:/ssh-agent

Below is my Dockerfile

FROM centos:7
EXPOSE 6653

RUN yum -y update &&
yum -y groupinstall ‘Development Tools’ &&
yum -y install vim mlocate flex flex-devel net-tools gdb screen &&
yum -y install autoconf libtool &&
yum -y install libssh2 libssh2-devel libxml2-devel openssl-devel readline-devel ncurses-devel &&
yum -y install initscripts

RUN mkdir -p /var/run/sshd
RUN yum -y update
RUN yum install -y openssh-server
RUN ssh-keygen -A
RUN ssh-keygen -t rsa

Tried running sshd in docker by

/usr/sbin/sshd -D

None of the above methods worked for me.
I’m missing anything to be done inside a docker?