Tutorials Design Patterns in C#

Strangler Fig Pattern — Complete Guide

Strangler Fig Pattern — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of Design Patterns in C# on Toolliyo Academy.

8 min read Updated 8/22/2026

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Design Patterns in C# · Lesson 52 of 69

Strangler Fig Pattern

GoF Core ✓ → Enterprise ✓ → Cloud & Craft

Cloud & Craft · 3 — Microservices & interviews · ~6 min · Module 6: Microservices & Cloud Patterns

What is this?

Strangler Fig replaces a legacy system piece by piece — route new paths to new services while old paths stay on the monolith.

Why should you care?

ShopNest cannot rewrite the whole monolith in one big-bang release.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

// Gateway routes
Console.WriteLine("/catalog/** -> new CatalogService");
Console.WriteLine("/checkout/** -> legacy Monolith");
Console.WriteLine("migrate more routes over time; delete legacy when idle");

What happened?

Intercept at the edge, grow the new system around the old, then remove dead legacy.
Measure traffic per route before cutting over.

Practice next

Pick one ShopNest bounded context to extract.
Route its URLs to the new service.
Compare responses in shadow mode if needed.
List next three routes to migrate.
Add metrics per routed path.

Remember

Incremental replacement. Route-based cutover. Retire legacy deliberately.

ShopNest catalog extraction

Catalog routes move first; checkout stays legacy temporarily.

Outcome: Risk stays small; value ships early.

Interview prep for this lesson

Practice these questions aloud after reading—each links to a full structured answer.

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Abstract Expression (IExpression):?

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Component (ICoffee):?

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