Your Environment is Wrong

"But, it works when I do it, so your environment must be wrong."

When I first heard that comment I took it seriously.  What could be wrong with our environment?  Why couldn't we install the application? 

Not different, because our UAT and Production environments are different than the development environments for a lot of reasons, but wrong.  I searched for something wrong.  Occasionally, I did find something wrong, but as we put more and more applications on to our UAT and Production boxes the number of things that were wrong obviously diminished to the point where their is not a whole heck of a lot that can be wrong.  The differences, however, are still there.  Differences that may prevent the application from installing or working correctly.

• clustered environment - we operate in a clustered environment, so never, ever think that this is the only application that is being installed on this server and never, ever think that it is the only instance of your application which is running
• not a clean environment - the odds are that we've installed your application before - sometimes once or twice before and in some cases a hundred times before - never assume that the environment is "clean" because the odds are that there are remnants of other installs of yours left around
• multiple installs - never assume that just because there is some manual configuration at the end that needs to be done that it is "no big deal" because in our UAT and Production environments we need to do the installs multiple times so that any manual configuration that needs to be done will be done multiple times, giving us plenty of opportunity to make a mistake

"Mistakes"?  Yes, we sometimes make mistakes when manually configuring an application.  Considering that in the UAT and Production environments we are going to be installing and manually configuring your application seven times or more, once we add more servers, this gives us seven chances to make a mistake.  Combine this with multiple releases to UAT and you've got a wonderful opportunity to introduce an unexpected bug, with the most likely problem being that the manual configuration was not saved on a specific machine.  Have the application self-configure itself where possible: prompt for data and complete the installation itself.

Oh, I forgot, you're only going to UAT and Production once, right?