Modernising a legacy platform without a big-bang rewrite
The instinct, when you inherit a platform of dozens of services accreted over a decade, is to propose a rewrite. It almost always fails — not for technical reasons, but because a rewrite freezes feature delivery while the business keeps moving, and the old system keeps changing underneath you.
I approach it differently. A few principles I keep coming back to:
Map before you move. You cannot sequence a migration you don’t understand. Service topology, the real call chains, which databases are actually coupled — this gets reverse-engineered into living documentation first. That map is what lets you cut the estate into a delivery sequence instead of a wish.
Phase it, and keep both systems honest. New and old run side by side. Change data capture — logical replication moving data continuously — means the target is never stale, so you can cut over a slice at a time and roll back a slice at a time. No weekend where everything changes at once.
Make the risky steps reversible. Every step that mutates shared state should know how to undo itself. This is the same instinct whether it’s a database migration or a deploy pipeline: design the compensating action alongside the forward one, so partial failure is safe rather than catastrophic.
Kill rented complexity where it pays. A sprawling estate accumulates vendor spend and coordination cost. Some of the highest-leverage work is consolidation — fewer services, fewer moving vendors, a schema that one person can reason about.
Document as you go, for humans and agents. Migration briefs, dependency maps, reverse-engineered specs — these aren’t overhead, they’re what reduces onboarding time and fragmentation while the team churns around a big change.
None of this is glamorous. But “the platform got quietly cheaper, more reliable, and easier to change, and we never stopped shipping” is a better outcome than a heroic rewrite that slips a year.
I take on remote consulting for exactly this kind of work — platform modernisation, migration architecture, and backend reliability. Get in touch.