Rolling Back a Build

Microsoft Outlook has a seemingly nifty feature called Recall Message that seemingly allows one to "unsend" a mistaken message. Unfortunately, due to the nature of email (and the space-time continuum), it doesn't really work that well... and the flood of "Jo Ann wants to Recall Message: Q3 Sales Data" emails makes everyone want to read it that much more. Attempting to rollback changes to an application works about as well and predictably.

Consider what would happen if you deployed changes that dropped a column in the database. While you could certainly copy old files back, there's no way to resurrect the lost column and its data. You could restore the database, but then you'd lose any intermittently entered data.

Of course, that's just the tip of the iceberg: there's configuration changes, third-party libraries, and all sorts of other not-so-straightforward changes that might have occurred. Reliably rolling backĀ  everything to a perfect previous state is nearly impossible. Writing a script to intelligently automate a rollback is even more difficult.

This is precisely why we don't have a special "rollback plan" that's used only in emergencies. Since such a plan would only get tested in rare cases (i.e. when something went wrong), chances are it will be out of date and likely make things even worse.

But what we do have is a "Re-execute promotion", which can effectively be be used to rollback changes. Assuming you have your deployment plan configured correctly, of course.. Let's consider the state of a given application. You'll note below that Release 3.5 (Build 16) was deployed to Production.

If we want to go back to Release 3.4 in production, we need to navigate to the promotion details of the production-promoted build for that release.

You'll notice there's a big button called "Re-execute Promotion". Clicking on that will run the production deployment plan using 3.4 Build 2's context. Here's what the plan looks like.

The actions "Deploy Artifact" and "Deploy config files" are both designed to look at the execution context to determine what to do. In this case, "Deploy Artifact" will deploy the artifact associated with 3.4 Build 2. This will ensure that whatever files were deployed with 3.4 Build 2 will always deployed with 3.4 Build 2.

Once the build has been re-deployed, the appropriate status is reflected in BuildMaster.

And like that, your changes are rolled back. Of course, this isn't a time machine and nothing (not even a time machine) can reliably and perfectly rollback all changes while keeping existing data. So, be careful using re-executions / rollbacks.