Docker offers to make it easy to deploy applications no matter what you infrastructure is. The problem is that you cannot just switch from one technology to another overnight just because it will help you solve certain issues. Moving to the new technology is an issue on its own, plus there is no technology that doesn’t come with its own issues. With Machinery we want to help you make the transition from VMs to containers as smooth as possible.

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This post was originally delivered as a presentation in LinuxCon Dublin 2015.

Let’s assume you have a server running a web application that uses Rails, Apache and MariaDB. We will use Machinery to create a System Description from this server which we will manually review and then allow machinery to automatically detect the respective workloads. Finally we will use machinery to verify that the see the differences between the original system and the resulting containers.

On my case I will use Portus as my Rails application.

Our work flow will look more or less like this:

Work flow

Creating a system description

First of all you will need to make sure you can access the server without requiring a password by copying your ssh keys into the server.

ssh-copy-id root@192.168.1.100

This is required because machinery will open an ssh connection and run a set of commands in order to evaluate the information inside the server. Then go ahead and inspect the server in order to create a system description.

machinery inspect --name portus --extract-files 192.168.1.100

The option --name is the name we want to give to our system description. The option --extract-files will make a copy of every file except those that are the default from an RPM package.

Once machinery has finished a folder named wordpress will be created inside /home/USERNAME/.machinery. If you have a pick into this folder you will find a file called manifest.json which is the physical representation of the system description and a files directory containing the extracted files.

You can easily open the system description with your favorite text editor but machinery also provides a show command for easy access.

machinery show portus --html

The additional --html option will tell machinery to start a web server on your local machine which will help us have a more interactive look about how this server has been set up. By omitting this option you will get access to the same information as text through the CLI.

Your default browser will open up with all the information about the wordpress system description. From here you can manually see in detail every configuration file, package and service that was running in order to write your Dockerfile.

HTML View

This feature on its own will help you out a lot because you can translate all this information not only into a Dockerfile but also into a configuration management system.

Containerizing

For the particular case of Rails (using MariaDB and Apache2) we’ve implemented a really nice feature into machinery that will allow you to only run a command and get the Dockerfiles created for you and also the docker-compose files so you can orchestrate your application once it has been containerized.

In order to do this you need to tell machinery to containerize a system description whose files have been extracted (in our case the wordpress system description)

machinery containerize --output-dir /tmp/containers portus

The required --output-dir tells machinery where you want your containerized version of the server to be saved.

Now we can go to /tmp/containers/portus and have a look. Machinery has created a set of files for us to run a containerized version of our application. The details on how to set it up and get it running will be inside the README.md file.

The first thing we need to do is to run the setup script.

./setup.rb

This script is unique depending on the application that was containerized. In the case of Portus it sets up a database container so that our web container can connect to it.

docker-compose up

Docker compose will start an instance of all the required containers. For Portus this means a web, a db and a registry container and allow you to access them from your local machinery through port 3000.

Voila! You just got yourself a containerized version of your application. How cool is that?

Introspection

Now this sound very nice but once you’ve done all this (specially if you are writing your own Dockerfiles or CMS recipes, modules, etc) you might want to check what is inside your resulting containers.

machinery inspect-container portus_db

At this point I could just show the portus_db system description and have a look if everything is the way I expect it to be but we can go one step further and compare it to the portus system description. This way I can make sure what the differences are between the container and the VM.

machinery compare portus portus_db

I could have added the --html option but I won’t so you can see the cli view of machinery. It was designed to play well with your other *nix commands so you could easily do something like this, to determine if there is a difference in the MariaDB package.

If there were no differences machinery would ommit this information. For this reason I’ve created a contianer with a different MariaDB version

machinery compare portus portus_db --no-pager | grep mariadb
* mariadb (version: 10.0.21 <> 10.0.20)
* mariadb-client (version: 10.0.21 <> 10.0.20)
* mariadb-errormessages (version: 10.0.21 <> 10.0.20)

You can easily spot the differences here. Now it’s up to you to change your Dockerfile or CMS files in order to add the right version of the package you’d like to install.

Summary

As you can see Machinery can be very useful to start deploying your applications as docker containers. Inspect an existing system and understand how it was configured using the inspect and show commands respectively. Write your Dockerfiles and build your docker images which you can then also inspect and compare to the original system using the inspect-container and compare commands.

While doing this remember to have a lot of fun and share back how you used machinery in your own project.