Wednesday, April 16, 2014

Continuous integration versus delayed integration

A vigorous area of debate in the development and architecture community exists around the value of Continuous Integration. To give context, when a software development team gets to a certain amount of concurrent work that involves multiple teams making changes in the same codebase, there are two main ways to handle this:

  • Each individual stream of work take a copy of the code and start working on their own
  • Each team coordinate all work streams within the same codebase

In my experience, the former method seems like a great idea, especially when folks start worrying about "what happens when project A impacts project B's timeline?". Everybody just works on your own feature and at the end of each team's work stream, just merge all the individual team's efforts back together in a shared location. The great advantage here is that if Feature A is pulled from the delivery, Feature B can be deployed independently. What is frequently overlooked is the fact that eventually, Features A and B still need to be mixed together. The longer we wait to do this, the greater the risk of integration problems and the less time we have to resolve them.

On the other hand, having everybody pushing work into the same development stream immediately introduces some problems that need to be resolved at build time. It's immediately necessary to have a process to allow reconciling competing Features and disable features should it not be complete before delivery. The major downside continuous (or at least frequent) integration is that individual developers and Feature teams are a bit slower day to day as they uncover unanticipated problems due to competing requirements in the various work streams, but the upside is that these are discovered early in the process instead of at a very late stage.

In short, delayed integration doesn't actually save any time in the long run as the will eventually still manifest themselves, just later in the process when you have less time to fix them. To all folks doing multi-stream development, seriously investigate limiting your work to "one branch per environment", and work out how to independently configure the environments to know which features they should enable.

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