13. Creating SSH Enabled Containers

In this chapter, you will learn how to communicate with Julia between different Docker containers. One uses SSH for this. The condition is that you can set up the connection without using a password by using SSH keys.

The article Dockerize an SSH service uses Ubuntu 16.04 as the base image. However, Julia 1.0 and higher needs Ubuntu 18.04, so we have changed the Dockerfile. This version of Ubuntu also requires that you create a user with administrator rights when you use SSH to connect.

You create a Docker container using a Docker image. You need a Docker installation file to create an image. By default, the file is called Dockerfile.

Once you have started the container, you make it suitable for a passwordless SSH connection.

Finally, you install the software needed for the application, including Julia.

See also the Pact book Julia 1.0 Programming: Installing Julia from binaries

Contents

• 13. Creating SSH Enabled Containers
• Activity 13.1: Create local SSH keys
• Activity 13.2: Create the Container
• The Dockerfile
• Activity 13.3: Install Julia
• Activity 13.4: Test the container.
• Exercise 13.1: Create a Second Container
• Summary

Activity 13.1: Create local SSH keys

You need SSH keys for passwordless Julia communication between Docker containers.

Prerequisites

• Your system has Ubuntu 20.04 that runs on an Intel x86 processor.
• You have started your computer.
• You haven't created the SSH keys before.

In this activity you will:

1. Check previously created keys.
2. Create local SSH keys.

Step 1: Check previous created keys

The folder .shh contains your keys if you have them created before.

Response

ls: cannot access '.ssh': No such file or directory

You haven't created the key before, go to step 2.

total 16
-rw------- 1 rob rob 3389 okt  8 16:48 id_rsa
-rw-r--r-- 1 rob rob  748 okt  8 16:48 id_rsa.pub
-rw------- 1 rob rob 1554 nov 17 14:56 known_hosts
-rw------- 1 rob rob 1554 nov 17 14:08 known_hosts.old

You have created the keys before, no further action is required. The file id_rsa.pub contains your public key. Later on, we will create a copy of it in the SSH enabled container.

Step 2: Create local SSH keys on your computer

The openssh-client software is needed to create the keys.

See SSH Connection Refused (Causes & Solutions)

Activity 13.2: Create the Container

When you want to create a container you need an image. An image is created from a Dockerfile.

Prerequisites:

• Your system has Ubuntu 20.04 that runs on an Intel x86 processor.
• You have started your computer.
• You have installed Docker.

In this activity you will:

1. Create a Dockerfile in the folder test_sshd.
2. Create a Docker image eg_ssdh and the container test_sshd.
3. Create a user rob, who has administrator rights.

The Dockerfile

FROM ubuntu:20.04

RUN apt-get update && apt-get install -y openssh-server
RUN mkdir /var/run/sshd
RUN sed -i 's/PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config

# SSH login fix. Otherwise, the user is kicked off after login
RUN sed 's@session\s*required\s*pam_loginuid.so@session optional pam_loginuid.so@g' -i /etc/pam.d/sshd

ENV NOTVISIBLE "in users profile"
RUN echo "export VISIBLE=now" >> /etc/profile

EXPOSE 22
CMD ["/usr/sbin/sshd", "-D"]

Step 1: Create a Dockerfile in the folder test_ssh

You create the file Dockerfile in the folder e.g. test_ssh.

Step 2: Create a Docker image eg_sshd and the container test_sshd

You need an image before you can create a Docker container.

Step 3: Create a user rob, who has administrator rights

Adding user `rob' ...
Adding new group `rob' (1000) ...
Adding new user `rob' (1000) with group `rob' ...
The home directory `/home/rob' already exists.  Not copying from `/etc/skel'.
adduser: Warning: The home directory `/home/rob' does not belong to the user you are currently creating.
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Changing the user information for rob
Enter the new value, or press ENTER for the default
    Full Name []: Rob Bontekoe
    Room Number []:
    Work Phone []:
    Home Phone []:
    Other []:
Is the information correct? [Y/n] Y

To run a command as administrator (user "root"), use "sudo <command>". \nSee "man sudo_root" for details.

Activity 13.3: Install Julia

Installing Julia is done in the same way as you did before.

Prerequisites:

• Your system has Ubuntu 20.04 running on the Intel x86 processor.
• The container test_sshd exists.
• The container has the user rob, who has administrators (sudo) rights.

In this activity you will:

1. Download the Julia binary and copy it to the container.
2. Install Julia and test the installation.
3. Create a symbolic link to start Julia from everywhere.

Step 1: Download the Julia binary and copy it to the container

With the command docker cp you can copy files to a container.

total 102796
-rw-rw-r-- 1 rob rob 105260711 Nov 17 10:17 julia-1.5.3-linux-x86_64.tar.gz

Step 2: Install Julia and test the installation

Unpack the .tar.gz file and test if Julia starts.

total 102804
drwxr-xr-x 8 1337 1337      4096 Nov  9 18:56 julia-1.5.3
-rw-rw-r-- 1 rob  rob  105260711 Nov 17 10:17 julia-1.5.3-linux-x86_64.tar.gz

   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.5.3 (2020-11-09)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia>

Step 3: Create a symbolic link to start Julia from anywhere

It is easier if you can start Julia from any folder.

Activity 13.4: Test the container.

Prerequisites:

• You have an SSH enabled container.
• You have created the SSH authorized_keys See.

In this activity, you will:

1. Copy your public key to the container.
2. Test the SSH connection with the container.

Step 1: Copy your public key to the container

You copy the public key you created in activity 13.1 to the container for passwordless authentication.

You get the next message:

The authenticity of host '172.17.0.2 (172.17.0.2)' can't be established.
ECDSA key fingerprint is SHA256:0qEmNoH8hb1OC73Hcecf4iY44vKAnLYOc6jNsdkkM2U.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes

Type yes and enter your password.

Step 2: Test the SSH connection with the container.

Test if it works fine.

Welcome to Ubuntu 20.04.1 LTS (GNU/Linux 5.4.0-53-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

This system has been minimized by removing packages and content that are
not required on a system that users do not log into.

To restore this content, you can run the 'unminimize' command.

Exercise 13.1: Create a Second Container

You will create a second Docker container that we will use for the AppliAR module.

Create a second container test_sshd2:

• You don't have to create the keys again!
• Use the same image eg_sshd.
• Start at Activity 13.2: Create the Container - step 2-2. Use an different port number for ssh (2223): docker run -d -p 2223:22 –name test_sshd2 eg_sshd
• The name of the administrative user can be kept the same: rob.

We will use both containers in chapter 14.

Summary

How do you build an application? Commonly, you run your code in a container. The philosophy we use is that each Julia module is a separate application.