The problems of multi-tenancy: the development model

in large enterprises AEM project tends to attract many different interested parties, which all love to make use of the features of AEM. They want to get onboard the platform as fast as they can. And this can be a real problem when it comes to such a multi-tenancy AEM platform.

In the previous post I wrote about the governance problems with such projects and all the politics involved in it. These problems pursue also in the daily business of the development and operation of such platforms.

Many of these tenants already have their development partners and agencies, which they are used to work with. These partners have experience in that specific area and know the business. So it’s quite likely, that the tenants continue to work with their partners also in this specific project. And there the technical problems starts.

Because at that point, you’ll realize, that you have multiple teams, which rarely collaborate or in worst case not at all. Teams which might have different skill levels, operate in different development models and use a different tooling. And each one of these teams gets its own prioritization and has its own schedule, and in most cases the amount of communication between these teams is quite low.

So now the platform owner (or the development manager on behalf) needs to setup a development model, which allows these multiple teams to feed all their results into a single platform. A model which doesn’t slow down your development agility and does not negatively impact the platforms stability and performance. And this is quite hard.

A number of these challenges are (note: most of them are not specific to AEM at all!):

  • How can you ensure communication and collaboration between all development parties? That’s often a part, which is left out (or forgotten) during time and budget estimation, therefor the amount of time spent on it is reflecting this fact. But that’s the most important piece here.
  • On the other hand, how do you make sure, that overhead of communication and coordination is as low as possible? In most cases this means, that each party gets its own version control system, its own maven module and its own build jobs. This allows a better separation of concerns during development and build time , but just postpones the problem. Because …
  • How you avoid the case, that multiple parties use the same names, which have to be unique? For example the same path below /apps or the same client library name? It’s hard to detect this at development time, when you don’t have checks, which cover multiple repositories and maven modules.
  • Somehow related: How do you handle dependencies to the same library but with different versions? Although OSGI supports this also during runtime, AEM isn’t really prepared for such a situation, that you should have a library in both version 1 and version 2. So you need to centrally manage the list of 3rd libraries (including version numbers), which the teams can use.
  • A huge challenge is testing. When you managed to deploy all delivered artifacts to a single instance (and combining these artifacts into deployable content packages often imposes its own set of problems), how do you test and where do you report issues? How happens the  triaging process to assign the issues to the individual teams for fixing? This can cause very easily a culture of blaming and denying, which make the actual bug fixing part very hard.
  • The same with production problems. No tenant and therefor no development team wants to get blamed for bringing down the platform because of some issue, so each problem can get very political, and teams start to argument, why they are not responsible.
  • And many more…

These are real world problems, which hurt productivity.

My thoughts how you can overcome (at least) some of the problems:

  • The platform owner should communicate open to all tenants and involved development teams, and encourage them to adhere to a common development model.
  • The platform owner should provide clear rules how each team is supposed to work, how they create and share their artifacts, and also clear rules for coding and naming.
  • The platform owner should be in charge for a small team which is supporting all tenants and all development teams and helps to align requirements and the integration of the different codebases. This team is also responsible for all the 3rd party library management and should have write access to the code repositories of all development teams.
  • Build and deployment is centralized as well.
  • Issue triaging is a cross-team effort.

This is all possible in a setup, where the platform owner is not only a function, which is not only responsible to run the platform, but also allowed to exercise control over the deployment artifacts of the individual parties.

Some sidenote: There is an architectural style called „micro services“, which seems to get traction at the moment. It claims to address the „many teams working on a single platform“ problem as well. But the whole idea is based on the split of monolithic application into single self-contained services, which does not really apply to this multi-tenancy problem, where every tenant wants to customize some aspects of the common system for itself. If you apply this approach to this multi-tenancy problem here, you end up with a multi-platform architecture, where each tenant has its own version of the platform.

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