Tips and Tricks #120: Apply Strangler Fig Pattern for Legacy Migration

Gradually replace legacy systems by routing traffic to new implementations incrementally.

Code Snippet

// API Gateway routing configuration
// nginx.conf or API Gateway rules

# Route new endpoints to modern service
location /api/v2/orders {
    proxy_pass http://new-order-service:8080;
}

# Legacy endpoints still go to monolith
location /api/orders {
    proxy_pass http://legacy-monolith:8080;
}

# Gradually migrate by feature flag
location /api/users {
    set $backend "legacy-monolith:8080";
    
    if ($http_x_use_new_service = "true") {
        set $backend "new-user-service:8080";
    }
    
    proxy_pass http://$backend;
}

Why This Helps

• Zero-downtime migration
• Reduces risk with incremental changes
• Allows rollback at any point

How to Test

• Verify routing works correctly
• Compare responses between old and new

When to Use

Migrating from monolith to microservices, replacing legacy systems.

Performance/Security Notes

Start with low-risk, well-understood features. Monitor closely during transition.

References

• https://martinfowler.com/bliki/StranglerFigApplication.html

Try this tip in your next project and share your results in the comments!