5 Ways to Break Up Your Monolith Without Breaking It Down

If you are here, most probably your aging monolith is actively bleeding money through mounting technical debt and you’re looking for a way out. If so, migrating to microservices might be your option. However, nearly 78% of microservices migrations fail when attempted as a “big bang” rewrite. 

Modern software modernization approaches offer a safer path without risking your entire business on a massive rewrite. And that’s what we are going to discuss in this read.

1 – Strategic Decomposition Planning

Before writing one line of code, you need to plan what pieces to extract and when in order to facilitate a successful migration. Look for areas of your monolith that already have low dependencies and clear responsibilities. These “seams” in your application are ideal extraction targets.

Practical decomposition steps:

• Visualize a dependency graph of how your modules interact;
• Measure call frequency between components to identify tight coupling;
• Keep a record of which teams own which parts of the codebase;
• Map business capabilities to technical components.

Prioritization metrics:

If you spend at least 30% of your migration timeline on planning, your success rate might be 65% higher compared to companies that rush to implementation. As Netflix architect Adrian Cockcroft noted during their transition: “If you can’t build a well-factored monolith, what makes you think microservices will help?”

2 – API Gateway Integration

An API gateway is like a traffic cop for your evolving architecture. It directs requests to either your monolith or new microservices and presents a uniform API to clients.

Gateway responsibilities:

• Rate limiting and throttling;
• Request routing by path, method, or payload;
• Error handling and retry logic;
• Authentication of incoming requests;
• Analytics and monitoring;
• Response caching.

You may also use what Netflix calls “traffic shadowing” i.e., duplicating requests to both monolith and microservices and comparing responses prior to cutting over traffic.

Implementation metrics:

3 – The Strangler Fig Pattern Implementation

The strangler fig pattern (named after a vine that gradually overtakes trees) is a practical method of incremental migration that doesn’t affect your business.

Rather than directly replacing your monolith, you build new features as microservices while gradually “strangling” the old system as its responsibilities are moved to the new architecture.

Implementation strategy:

1. Insert a facade or proxy layer that intercepts calls to the monolith;
2. Build new services outside of the monolith for specific operations;
3. Gradually route traffic through the facade to the monolith or new services;
4. Decommission monolith functionality as services stabilize.

4 – Payment Module Isolation with Docker

Payment processing is often the perfect candidate for businesses looking to make their first extraction. It has well-defined boundaries, stringent security needs, and usually requires different scaling than the rest of the application. By containerizing payment functions, you can enjoy immediate isolation benefits, even before fully transitioning to microservices.

Here’s a quick rundown of the steps for implementing Docker:

1. Pinpoint the boundaries and dependencies of your payment module.
2. Set up a separate database specifically for payment data.
3. Create a Docker container that has only the essential runtime dependencies.
4. Use Docker Compose or Kubernetes to configure network isolation.

Security benefits:

• Encryption keys stored separately from transaction data;
• 76% reduction in PCI compliance scope;
• Resource limits preventing container escape attacks;
• Payment processing isolated from customer data.

5 – Incremental Rollout Strategies

Even with the best planning, moving to microservices can be risky. Smart rollout strategies can reduce these risks and provide backup options if things go sideways. 

Feature flags are a great way to manage which users get to see the new microservice features, allowing you to switch between the old and new versions without redeployment.

A SaaS company successfully used LaunchDarkly to manage their migration, and the results were impressive:

• They started with just internal users, making up 2% of their traffic.
• Then expanded to beta customers, reaching 10% of the traffic.
• They rolled out the changes by geography, gradually increasing to 25%, 50%, 75%, and finally 100%.
• Throughout the process, they kept the option to revert to the monolithic structure instantly if any issues popped up.

Blue-green deployment pattern:

• “Blue” environment: Current production (monolith)
• “Green” environment: New microservices
• Traffic routed to blue by default
• Testing conducted in green
• Instant cutover when ready
• Immediate rollback capability

On a Final Note

The journey from monolith to microservices doesn’t have to be chaotic. By taking an incremental approach, you can achieve modernization without business disruption.

The most common pitfall remains overambition though, when you attempt to migrate too much, too quickly. Companies that succeed typically:

• Plan for 30-50% longer timelines than initially estimated;
• Limit initial extractions to 2-3 well-defined services;
• Measure business metrics, not just technical ones;
• Maintain the ability to operate in hybrid mode indefinitely.