Thursday, 25 September 2014

Docker-izing MapGuide

There was a motivation behind this public service announcement.

It was part of my investigations into being able to deploy MapGuide as a Docker container.

What is Docker you may ask? Have a read of their introduction page.

TL;DR? Docker is a tool that allows you to run and deploy software inside virtualized software containers. This is not a heavyweight VM like VirtualBox and their ilk. This is something that leverages existing features in the Linux Kernel to provide "lightweight" VMs with very low overhead.

A docker-ized application gives us various benefits:
  • Your application and its dependencies are all self-contained and will not interfere with anything outside of its container and vice versa.
  • Deployment is dead simple. No figuring out what pre-requisites that have to be installed. They'll all be part of the docker image that you can pull down with a single command.
  • Your application can run in host environments that the application was not originally compiled/tested for. Build once, run anywhere (where docker is installed :))
There's many more benefits than what's listed here. So you can probably see where a docker-ized MapGuide would really be useful from a developer and administrator perspective.

But there is a catch to all this goodness. Firstly you need a Linux distribution that uses Linux Kernel v3.8 or newer as that contains the required OS virtualization features needed for Docker to work.

Secondly, you need to run a 64-bit Linux distribution as that is what Docker only supports. In order to run MapGuide within a Docker container, we need a way to run a 32-bit MapGuide within a 64-bit Linux environment as Docker can only be run from within a 64-bit Linux host and as previously mentioned, we still don't have a functional 64-bit Linux build of MapGuide yet :( So the workaround is to install the required 32-bit packages, which you can find in my previous post.

So after applying all of this newly acquired knowledge, allow me to introduce my first Docker image for MapGuide.

This is a CentOS 6 base image that has the following software and packages pre-installed:
From this base image, you can build your own docker image that installs your own MapGuide data, applications and configurations and deploy/run that image as a docker container.

Here's a basic example of getting a docker-ized MapGuide up and running with mapguide-rest and some sample data packages using 64-bit Ubuntu 14.04 using the above docker base image:

Firstly, we install the docker package like so

sudo apt-get install

Then make a new directory and create a file named Dockerfile

Put the following text into the Dockerfile. The comments should be self-explanatory. 

# This image is based from the MapGuide docker base image
FROM jumpinjackie/mapguide-base
# Install additional packages, load your MapGuide applications and data, etc.
# Download Sheboygan dataset
RUN wget -P /usr/local/mapguideopensource-2.6.0/server/Packages
# Download Melbourne dataset
RUN wget -P /usr/local/mapguideopensource-2.6.0/server/Packages
# Download mapguide-rest 0.10
RUN wget
# Set up install location for mapguide-rest
RUN mkdir -p /usr/local/mapguideopensource-2.6.0/webserverextensions/www/rest
# Extract mapguide-rest
RUN unzip -d /usr/local/mapguideopensource-2.6.0/webserverextensions/www/rest
# Fix up permissions of the cache directory (for tiles and smarty templates)
RUN chown daemon:daemon /usr/local/mapguideopensource-2.6.0/webserverextensions/www/rest/cache
# Expose the web server port to the world outside the container. The default port is 8008
# Run supervisor, that will start the MapGuide Server and Apache httpd server
CMD ["/usr/bin/supervisord"]

Now save the Dockerfile, and run the following command to build the docker image from that file

sudo docker build -t my-mapguide-app .

This command will download the mapguide-base docker image which will take a few moments depending on your download speed. This is only downloaded once and will remain until you explicitly remove this base image.

my-mapguide-app will be the name of the docker image, which you'll need to reference when you will run a container from it, which is what we will do next. But before we do that, we should list our docker images and see if our new image is there.

sudo docker images

Now that we have confirmation that our image has been created, we can create a container from it like so.

sudo docker -d --name mapguide -t my-mapguide-app

The -d switch indicates that this container will run in the background. The --name switch assigns the name mapguide to this container so we don't have to remember a long UUID for referencing this container in future operations, which is what is outputted when the command succeeds.

Finally the -t switch indicates that we want to create a container from the my-mapguide-app image that we just created.

Now that we have started a container, we now have:

  • MapGuide Server running
  • The Sheboygan and Melbourne sample data packages downloaded to the Packages directory of the MapGuide Server installation directory
  • The mapguide-rest extension installed
  • Apache HTTP Server running on port 8008 which is exposed
We now just need to know what IP address has been assigned to this container. To do that, we can run the following command

sudo docker inspect mapguide | grep IPAddress

Now that we have an IP address, we can see if things are in order by firing up the Site Administrator

If we login and go to the Manage Packages page, we can see the packages we've downloaded as part of building our my-mapguide-app Docker image are there.

Now load these packages, and go to the mapguide-rest sample apps landing page just to see that the extension was installed.

If the samples on this landing page work, you have just verified that your docker-ized MapGuide container is now fully operational.

So that's a little run-through of how to get MapGuide running in a Docker container. Now the other thing about Docker that is really awesome is that the big players in Cloud Computing already (or starting to) support Docker containers as a PaaS deployment option.

Can you say MapGuide on the cloud?

Now just to clarify, MapGuide on the cloud via IaaS is already relatively easy. I, the AWS noob easily got a MapGuide demo site on Amazon EC2 set up over the GovHack weekend, which stayed up long enough to impress the judges to win some awards.

However the IaaS approach to deployment puts a burden on you to maintain the actual infrastructure (VMs, etc). As a case in point, our GovHack demo site has been taken down because I butchered my Amazon EC2 instance due to a combination of failure to act on an important email alert on this issue from Amazon and my general AWS noob-ery.

The PaaS approach lets you focus solely on deploying the applications, without having to worry about the underlying infrastructure. MapGuide as a Docker container enables the possibility of using this cloud deployment option.

Hopefully this post has sold you on the power and potential of Docker and how having MapGuide as a docker container may open up deployment and development scenarios that were previously not possible or took a lot of manual effort.

As for that Docker base image I linked to, that is just the tip of the iceberg. I'm just getting my feet wet with Docker and foresee many future blog posts on this topic as I learn more about what Docker can and can't do.

I can see the possibility of having different base images in the future:
  • Individual Server and Web Tier Docker images. Imagine how easy it would be to set up a load-balanced cluster via Docker containers? I'd have to grok how these containers communicate first, but the possibilities are very interesting.
  • Web Tier images tailored for the PHP or Java installation profiles.
  • Many others?
I also wouldn't comfortably say that the above docker image is currently production-ready. There's questions that need to be answered:
  • How do we handle the case of a mgserver or httpd process falling over on a background docker container?
  • How can we easily access and manage log files in a docker container?
  • How can we perform repository backup/restoration operations within a docker container?
  • How do we perform $MAPGUIDE_SERVER_ADMIN_TASK within the docker container?
If you have an idea on how these questions can be answered, I invite you to help improve the design of this docker image or to enlighten me on the comments below.

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