Monolith to Microservices migration

Monolith to Microservices Migration: "Shrink the Monolith, Grow the Microservices"

1. Strangler Pattern: "Replace and Shrink"

• Concept: Gradually replace parts of the monolith with microservices.
• Execution: Pick a feature, carve it out as a microservice, and redirect traffic. Repeat until the monolith is gone.
• Advantage: Low-risk, step-by-step approach.

2. Domain-Driven Design (DDD): "Boundaries to Services"

• Concept: Break down the monolith into logical business domains.
• Execution: Identify natural boundaries in your application and turn each into a microservice.
• Advantage: Aligns services with business functions.

3. Vertical Slice: "Slice and Dice"

• Concept: Split the monolith into vertical slices, each representing a business capability.
• Execution: Start with a simple slice, build a microservice, and integrate. Move to the next slice.
• Advantage: Manageable chunks for easier migration.

4. Business Capability: "Function First"

• Concept: Focus on individual business capabilities.
• Execution: Isolate and migrate each business function as a microservice.
• Advantage: Cohesive, loosely coupled services.

5. API Gateway: "Single Entry, Many Paths"

• Concept: Use an API Gateway to route requests to microservices.
• Execution: Start routing specific requests to new microservices through the gateway. Expand as needed.
• Advantage: Simplifies client integration and transition.

6. Event-Driven: "React and Evolve"

• Concept: Migrate event-driven components.
• Execution: Build microservices that communicate via events, starting with natural event-driven areas.
• Advantage: Supports loose coupling and scalability.

7. Parallel Development: "Two Tracks"

• Concept: Develop microservices alongside the monolith.
• Execution: Create new features as microservices, keep the monolith running, and gradually transition.
• Advantage: Experiment without disrupting production.

8. Modular Monolith: "Modular First, Micro Later"

• Concept: Refactor the monolith into modules.
• Execution: Modularize the codebase, then migrate each module to a microservice.
• Advantage: Prepares for a smoother transition.

9. Incremental Decomposition: "Start Simple, Scale Up"

• Concept: Begin with non-critical components.
• Execution: Migrate less complex parts first, then move to more complex ones.
• Advantage: Reduces risk, allows for learning.

10. Big Bang Rewrite: "All or Nothing (Avoid)"

• Concept: Rebuild the entire system as microservices in one go.
• Execution: Develop separately, switch over once complete.
• Advantage: Typically, none. It’s risky and time-consuming.

Key Considerations: "Test, Monitor, and Organize"

• Testing: Test each step thoroughly to ensure stability.
• Data Management: Plan for consistent and reliable data across services.
• Monitoring: Implement strong monitoring from the start.
• DevOps Practices: Adopt CI/CD, automation, and containerization early.
• Team Structure: Organize teams to support the microservices lifecycle.

This approach gives you a clear roadmap for moving from monolith to microservices, helping you choose the right strategy based on your specific needs and minimizing risks along the way.

High-Level Migration Strategies for various team sizes and application sizes

note

This table provides general recommendations and may vary based on your specific context and requirements. Always adapt the strategies to fit your unique situation.

A table which outlines each migration strategy, along with recommendations for team size and application size:

Strategy	Team Size Recommendation	Application Size	Description
Strangler Pattern	Small to Medium	Small to Medium	Gradually replace parts of the monolith with microservices.
Domain-Driven Design (DDD)	Medium to Large	Medium to Large	Break down the monolith into bounded contexts, aligning services with business domains.
Vertical Slice Approach	Small to Medium	Small to Medium	Split the monolith into vertical slices, each representing a business capability.
Decompose by Business Capability	Medium to Large	Medium to Large	Isolate and migrate individual business capabilities into microservices.
API Gateway Pattern	Medium to Large	Medium to Large	Use an API Gateway to manage and route requests to microservices.
Event-Driven Decomposition	Medium to Large	Medium to Large	Decompose by identifying and migrating event-driven components or processes.
Parallel Development (Forking)	Large	Large	Develop microservices in parallel while maintaining the monolith.
Modular Monolith	Small to Medium	Small to Medium	Refactor the monolith into a modular structure, then migrate modules to microservices.
Incremental Decomposition	Small to Medium	Small to Medium	Start with non-critical components, gradually moving to more complex ones.
Big Bang Rewrite (Not Recommended)	Large	Large	Rebuild the entire monolith as microservices in one go (highly risky).

Key Points

• Team Size:

  • Small: 1-5 developers.
  • Medium: 5-10 developers.
  • Large: 10+ developers.

• Application Size:

  • Small: Simple applications with a limited number of features and users.
  • Medium: Applications with moderate complexity, multiple features, and a growing user base.
  • Large: Highly complex applications with numerous features, modules, and a large user base.

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