Series 02 · 8 Parts· 1h 11m

The Strangler Fig Pattern & Incremental Migration

How to replace a legacy system slice by slice — routing, anti-corruption layers, and per-slice validation — without a big-bang rewrite.

Start reading · Part 1

Contents

01 What Is the Strangler Fig Pattern? 7 min read The strangler fig pattern modernizes a legacy system by growing a new one around its edges and shifting work across one piece at a time — until the old system can be retired.
02 Strangler Fig vs Big-Bang Rewrite 11 min read Strangler fig replaces a legacy system slice by slice while it keeps running; a big-bang rewrite rebuilds it in parallel and switches at one date. Here is the trade-off, and when a rewrite still wins.
03 The Strangler Fig Facade & Routing Layer 8 min read The strangler fig facade is the routing layer in front of a legacy system that sends each request to either the old implementation or a modernized slice — the seam that makes slice-by-slice migration possible.
04 Anti-Corruption Layer Explained 10 min read An anti-corruption layer translates between a modernized slice and the legacy system it still talks to — keeping the old data model and assumptions from leaking into clean new code.
05 How to Implement the Strangler Fig Pattern 9 min read A step-by-step playbook for implementing the strangler fig pattern — finding seams, standing up the facade, choosing the first slice, ramping traffic, retiring legacy, and knowing when the strangle is done.
06 Why Strangler Fig Projects Stall 10 min read Strangler fig migrations fail in recognizable ways: the strangle that never finishes, the facade that becomes permanent, slice boundaries drawn wrong. Here are the failure modes and how to avoid them.
07 Validating Each Slice: Parallel Run, Flags & Rollback 8 min read The three mechanisms that make each strangler-fig step safe — a parallel run for evidence, feature flags to ramp traffic at the facade, and per-slice rollback to contain a bad slice.
08 Strangler Fig Pattern Examples & Case Studies 8 min read How the strangler fig pattern actually unfolds — worked examples on a monolith, a mainframe batch system, and a forms-based application, from first seam to retired legacy.