Modernise the seams, not every system at once.

Locate

Find the boundaries where change becomes expensive.

Legacy is not an age. It is a constraint on safe, useful change. The most valuable starting point is often the seam where teams duplicate data, coordinate releases, diagnose failures across systems or wait for one specialist who understands the integration.

Mapping those boundaries reveals increments that can reduce operational risk while the wider estate continues to serve the business.

Transition

Apply the strangler pattern with operational accountability.

A new interface or service is only part of the transition. Teams also need to know which record remains authoritative, where reconciliation happens, how failure is observed and who can choose between rollback and forward repair.

• One named owner for the transition boundary.
• Explicit source-of-truth and data reconciliation rules.
• Observable failure states on both sides of the seam.
• A retirement condition for temporary integration paths.

Sequence

Sequence work to learn before the largest commitment.

Choose an increment that is important enough to expose the real constraints but bounded enough to recover. The first release should test the architecture and the delivery operating model together.

That evidence produces a better roadmap than a complete target-state diagram created before teams have met the current estate in production.