Full rewrites of legacy systems have a well-earned reputation for running over budget, over time, and sometimes failing outright. A phased approach is almost always the safer, more realistic path.
The strangler-fig approach
Rather than replacing everything at once, new functionality is built around the edges of the legacy system, gradually taking over responsibilities until the old system’s role shrinks to nothing. The business keeps running on working software throughout.
Sequencing the work by risk and value
Starting with the modules that are both highest-risk and highest-value gives the clearest early return, while lower-priority pieces can wait until capacity allows. This keeps momentum visible without requiring the whole system to be rebuilt before any value shows up.
Modernization done this way takes longer in calendar time but carries far less risk of a failed, disruptive cutover.
