What’s a legacy system? Some would say that it’s a system running on no longer supported components – old versions of software, impossible to upgrade databases, operating systems that were released before the Internet was a thing, or servers that still have Pentiums inside. Another way of looking at it would be when the number of people who know how the system works is fewer than the fingers on one hand and you are concerned that if anyone else retires, you will no longer be able to make any changes to the system.
Those are all true. There are plenty of corporations and government entities running systems that have some or all of those. Much of the backbone of UK government’s technology is based on systems built in the 70s, 80s and 90s. Our tax is collected, our benefits paid and our customs transactions policed by such systems.
There is, though, more to a legacy system than that. It could even be said that a legacy system is one that went live yesterday – because unless you have a plan to invest in your shiny new IT asset, all it will do by itself is decay and rust.
As systems get bigger and more complicated, whole areas of code will be looked at less and less frequently; familiarity with how that code works decreases. Personnel churn, whether in house developers or supplier staff, means that new people have less experience with the code than those who went before. Wholesale code reviews are rare. Code optimisation – revisiting already working code to re-factor it- as a way of teaching new staff how the whole thing works seems a forgotten discipline.
We talk now of technical debt – code that was fine when it was launched but is really holding back development of new capability now. It’s too complicated. It’s hard coded. It has dead ends. It doesn’t interface to new tools. This code can be a day old too.
IT systems are strategic assets, like bridges, tunnels, dams and roads. The internals need to be inspected, cleaned, operated and polished. Sure you can stand back and look at them and say how nice they are and how impressive the construction is. But the day you slow down on your maintenance is the day they become part of your legacy estate. You can pay now, or you can pay later, but you’re going to pay.