The real cost of ignoring legacy modernisation

The gap between knowing this and actually doing it is where most teams lose ground. Nobody bills you for neglecting legacy modernisation. The cost shows up somewhere else.

Architecture is the set of decisions that are expensive to reverse, which is the only reason they deserve the name. Assume whoever inherits this will have half your context and none of your patience.

Where the cost lands

• Time spent on work that should not have been necessary
• Enquiries that quietly never arrive
• Strangle the old system gradually rather than replacing it at once
• Rework, once the problem is finally visible

Big-bang rewrites are the most reliable way to lose two years. Where this goes wrong is almost never a lack of knowledge. Doing this properly once is usually cheaper than doing it approximately three times.

Making it stick

Every migration needs a way back. It is worth being explicit about, because assumptions differ quietly. Assume whoever inherits this will have half your context and none of your patience.

How to tell if yours is fine

The right architecture for a team of three is the wrong one for a team of thirty, and vice versa. Three things worth confirming about legacy modernisation before you move on:

• Someone can say what the current setup is without going to look
• Big-bang rewrites are the most reliable way to lose two years — and you know whether that is true here
• There is a way to tell whether the last change to this helped

If you are not sure where your systems currently stand on this, it takes us about an hour to find out.