MicroServices architecture style and its advantages over Monolith Application are known. I've tried to list down guidelines with respect to MicroServices when we want to split the Monolith.

1. Systematic Migration of
Monolith to Microservices
Pradeep A. Dalvi

2. Monolith Application
• Start out small
• Add new features
• Add new components
• Until one day you realize…

3. Monolith Application
• Conway’s Law
• Complex codebase
• Slow development process
• Complex provisioning
• Slow deployment

4. Why Microservices?
• Agility and velocity of developing new features
• Flexibility on required skillsets
• Depend on technologies, platform and languages
• Risk involved in upgrade
• Rapid deployments
• Scaling: Scale Out vs Scale Up
• Licensing, Hardware cost, FaultTolerance

5. How to move to Microservices?
• Big Bang rewrite?
• Extremely risky - “The only thing a Big Bang rewrite guarantees is a Big Bang!” --Martin
Fowler
• Application Modernization
• Split Monolith into small-small Microservices
• Two weeks for rewriting
• Two Pizza Rule by Jeff Bezos

6. Strategies
• Authentication
• IPC
• Define Boundaries
• Incremental Refactor
• Database
• Handling Partial Failures

7. Authentication
• SSO
• Distributed session
• Client-sideTokens
• Client-sideTokens with API Gateway

8. IPC
• Synchronous
• One-to-One (Request/Response)
• Asynchronous
• One-to-One (Notification or Request/Async Response)
• One-to-Many (Publish/Subscribe or Publish/Async Responses)
• Orchestration vs Choreography
• Define IDL

9. Define Boundaries
• Understand Business Capabilities
• Identify Domains using Domain-Driven Design
• Apply Single Responsibility Principle
• Data Models review
• Identify difficult parts

10. Incremental Refactor
• New Development shall happen in Microservices
• Split Frontend and Backend
• Extract Services

11. New development in Microservices
New
Requests
Old
Requests
API Gateway
Monolith
Service
Glue

12. Split Frontend and Backend
Browser Frontend Business Logic

13. Extract Services (Leaf)
Catalog Reviews Catalog
Reviews

14. Extract Services (Intermediate)
Payment
Order
Shipping Payment
Order
Shipping

15. Extract Services (…contd)
Payment
Order
Shipping

16. Database
• Splitting DatabaseTables/Columns
• Foreign Key Relationship
• Shared Static Data
• Shared Mutable Data
• Transactional Boundaries

17. Splitting Database
Order Shipping Order Shipping

18. Splitting Database
Order Id User Products Shipping
Order Id User Id Product Ids
Shipping Id Order Id Shipping

19. Splitting Database - Staging
Order Shipping Order Shipping Order Shipping

20. Foreign Key
Product Id Order Id Product Id
Product Catalog Order

21. Shared Static Data
• Duplication
• Static Data as Code or Config
• Separate Service
Catalog Shipping
State Cities PIN Area

22. Shared Mutable Data
Finance Shipping
Customer Service

23. Transactional Boundaries
• Single to SeparateTransactional Boundaries
• Try again later
• Abort entire operation
• DistributedTransactions

24. Handling Partial Failures
• Timeouts
• Limit number of outstanding requests
• Circuit Breaker
• Provide Fallbacks

25. Microservices Chassis Framework
• API Gateway
• Service registry and Discovery
• Circuit Breakers
• IPC
• Health Check
• Metrics
• Logging