Information architecture & content architecture

Recently I had a discussion in the AEM forums about how to reuse content. During this discussion I was reminded again at the importance of the way how you structure content in your repository.

For this often the term “information architecture” is used, but from my point of view that’s not 100% correct. Information architecture handles the various aspect how your website itself is structured (in terms of navigation, layout but also content). It’s most important aspect is the efficient navigation and consumption of the content on the website by end users (see the wikipedia article for it, ). But it doesn’t care about aspects like content reuse (“where do I maintain the footer navigation”), relations between websites (“how can I reduce work to maintain similar sites”), translations or access control for the editors of these systems.

Therefor I want to introduce the term “content architecture“, which deals with questions like that. The information architecture has a lot of influence, but it’s solely focused on the resulting website; the content architecture focusses on way, how such sites can be created and maintained efficiently.

In the AEM world the difference can be made visible very easily: You can see the information architecture on the website, while you can see the content architecture within CRXDE Lite. Omitting any details: The information architecture is the webpage, the content architecture the repository tree.
If you have some experience with AEM you know that the structure of the website typically matches some subtree below /content. But in the repository tree you don’t find a “header” node at the top of every subtree of a “jcr:content” node of a page, same with the footer. This piece of the resulting rendered website is taken from elsewhere, but not maintained as part of every page, although the information architecture mandates, that every page has a header and a footer.

Besides that the repository also holds a lot of other supporting “content”, which is important for a information architecture but not directly mandated by it. You have certain configuration which controls the rendering of a page; for example it might control which contact email address is displayed at the page footer. From an information architecture point of view it’s not important, where it is stored; but from a content architecture it is very important, because you might have the chance to control it at a single location, which then takes effect for all pages. Or at multiple locations, which result in changing it for individual pages. Or in a per-subtree configuration, where all pages below a certain page are affected. Depending on the requirement this will result in different content architectures.

Your information architecture will influence your content architecture (in some areas it even be a 1:1 relation), but the content architecture goes way beyond it, and deals with other “*bilities” like “manageability”, “evolvability” (how future proof is the content if there will be changes to information architecture?) or “customizability” (how flexible in terms of individualization per page/subsite is my content architecture?).

You can see, that it’s important to be aware of the content architecture, because it will have a huge influence on your application. Your application typically has a lot if built-in assumptions about the way content is structured. For example: “The child nodes below the content root node form the first-level navigation of the site”. Or “the homepage of the site uses a template called ‘homepage'” (which is btw also not covered by any information architecture, but an essential part of the content architecture).

In the JCR world there is the second rule of David’s model: “Drive the content hierarchy, don’t let it happen”. That’s the rule I quote most often, and even though it’s 10 years old, it’s still very true. Because it focusses on the aspect of managing the content tree (= content architecture), and that you should decide carefully considering the consequences of it.

And rest assured: It’s easier to change your application than to change the content tree! (At least if it’s designed properly. If it isn’t, … It’s even harder to change them both.)

AEM and docker – a question of state

The containerization of the IT world continues. What started with virtualization in the early 2000s has reached with Docker a state, where it’s again a hype topic.

Therefor it’s natural that people also started to play with AEM in docker (https://adapt.to/2016/en/schedule/running-aem-in-docker.html, https://www.linkedin.com/pulse/running-aem-docker-satendra-singh and many more).

Of course I was challenged with the requirement to run AEM in docker too. Customers and partners asking how to run AEM in docker. If I can provide dockerfiles etc.  I am hestitating to do it, because for me docker and AEM are not a really good fit (right now with AEM 6.3 in 2017).

Some background first: Docker containers should be stateless. Only if the application within the container does not hold any persistent state, you can shut it down (which means deleting all the files created by the application in the container itself), start it up, replace it by a different container holding a new version of the application etc. The whole idea is to make the persistent state somebody else’s problem (typically a database). Deployments should be as easy as starting new docker instances (from a pre-tested and validated docker images) and shutting down the old ones. Not working and testing in production anymore.

So, how does that collide with AEM? AEM is not only an application, but the application is closely tied with a repository, which holds state. Typically the application is stored within the repository, next to the “user data” (= content). This means, that you cannot just replace an AEM instance inside docker by a new instance without loosing this content (or resetting it to a state, which is shipped with the docker image). Loosing content is of course not acceptable.

So the typical docker rollout approach of new application versions (bringing new instances live based on a new docker image and shutting down the old ones) does not work with AEM; the content sitting in the repository is the problem.

People then came up with the idea, that the repository can stored outside of the docker image, so isn’t lost on restart/replacement of the image. Docker calls this “host directory as data volume” (https://docs.docker.com/engine/tutorials/dockervolumes/#locate-a-volume).

Storing the repo as data volume on the host filesystem

That idea sounds neat and of course it works. But then we have a different problem. When you start a new docker image and you mount this data volume containing the repository state, your AEM still runs the “old” version of your application. Starting the repository from a different docker image doesn’t bring any benefit then.

Docker image version 2 still starts application version 1.0

When you want to update your AEM application inside the repository, you would still need to perform an installation of your application into a running repository. Working in a production environment. And that’s not the idea why you want to use docker.
With docker we just wanted to start the new images and to stop the old ones.

Therefor I do not recommend to use docker with AEM; there is rarely a value for it, but it makes the setup more complicated without any real benefit.

The only exceptions I would accept are really short-lived instances, where hosting the repository inside the docker system isn’t a problem and purging the repo on shutdown is even a feature. Typically these are short-lived development instances (e.g. triggered by Continous integration pipeline, where you automatically create dedicated docker instances for feature branches). But that’s it.

And as a sidenote: This does not only affect TarMK-based AEM instances. If you have mongo-based instances, the application is also stored within the (Mongo-) repo. Just running AEM in a new docker image doesn’t update the application magically.

To repeat myself: This considers the current state. I know that the AEM engineering is perfectly aware of this fact, and I am sure that they try to adress it. Let’s wait for the future 🙂