Listening an episode of The Azure Podcast from June 2021 I heard about the offering of doing app migration by containerizing your applications. I looked this up through Microsofts documentation as well. A good summery is the diagram below illustrating the capabilities:

Azure Migration: App Containerization

On the one hand I can certainly see the business case for using this tool. Old LOB applications where the developers which made the app is long gone, the app will not need to be updated with neither bug fixes nor new features. If you already are using Azure and want to minimize your on-premise footprint - then using this method to “lift and shift” your LOB applications seems valid.

However - you are not setting yourself up for deploying anything new to this application. In that case you have to consider the 5 Rs:

  • Rehost
  • Refactor
  • Rearchitect
  • Rebuild
  • Replace

What the app containerization tool is actually helping you do is to rehost. But it’s limiting you to just rehosting and no future changes to the containerized application since it’s not generating images based on a code base, but rather from the functionality discovered on a running .NET app or Java app running on Tomcat. But as I mentioned - if the use case is that you have really old legacy applications that just run (and work) in your on-premise environment and that no one requests new features from or is going to be either refactored, rearchitected, rebuilt or replaced down the road - this tool seems valid to use when minimizing your on-premise foot print is one of your goals. In addition using PaaS-offerings like AKS or Web app services instead of spinning of VMs to run your old LOB applications seems like less configuration and less time consuming.

Given that enterprises most likely have a large portfolio of applications that fit the bill for these kinds of migrations I think this tool probably will be useful to many customers using Azure. But it’s important to remember the limitations of this approach and also have the 5 Rs in mind.