Dark infrastructure is undocumented but active software or services whose existence and function is unknown to system administrators -- despite the fact that it may be integral to the continued operation of documented infrastructure.
Dark infrastructure’s undocumented code may tie together pieces of known infrastructure, filling in needed functions. Without inspection of how software is operating, an administrator might never discover that dark infrastructure exists. Often dark infrastructure may not be noticed until something stops working.
An administrator may discover dark infrastructure when they look for the source of a problem and may learn where the unknown service is and how it functions while they attempt to correct the issue. Dark infrastructure can cause additional difficulties in troubleshooting, especially while it remains undetected.
There are any number of situations that can lead to undocumented infrastructure. For example, a vendor may add software services at the last minute and not take the time to document the changes. In other cases, changes may be made by individual administrators to correct issues after deployment. Either way, this quick, quiet work may correct the immediate issues but result in dark infrastructure that causes problems down the road.