Definition

The basic concept of a microservice is simple—it’s a simple, standalone application that does one thing only and does that one thing well. The objective is to retain the simplicity, isolation, and productivity of the early app. A microservice cannot live alone; no microservice is an island—it is part of a larger system, running and working alongside other microservices to accomplish what would normally be handled by one large standalone application. – Hands-On Software Architecture with Golang

Definition

• Each microservice is:
  • autonomous
  • independent
  • self-contained
  • and individually deployable
  • and scalable.

Concepts

• Independent deployability

  • criteria for this: make sure microservices are loosely coupled
    • be able to change one service without having to change anything else

• Modeled around a business domain

  • definition of service boundaries (see DDD)

• Owning their own state

  • hide internal state (same as encapsulation in OOP)
  • clean delineation between internal implementation details and external contract
    • be backward-compatible
  • hide database that backs the service
    • avoid DB showing

• Size

  “A microservice should be as big as my head” - James Lewis

  • keep it to the size at which it can be easily understood

• Flexibility

  “Microservices buy you options” - James Lewis

  • they have a cost and you must decide whether the cost is worth the options you want to take up

• Alignment of architecture and organization

  • Conway’s Law
  • have team vertically organized
    • same team owns front-end, business logic, data, back-end, security
      • a so called stream-aligned team

Advantages

• use the componentization strategy
  • divide and rule more effectively
  • with clear boundaries between components.
• create the right tool for each job in a microservice
• testability
• improved developer productivity and feature velocity.

Resources

• from Building Microservices (2nd edition)

Articles

• 2024-02-01 ◦ The False Dichotomy of Monolith vs. Microservices
• 2023-10-04 ◦ The Complete Microservices Guide - DEV Community
• 2022-12-15 ◦ Sam Newman: Practical Implications of Microservices in 14 Tips (old but still good)
• 2022-09-13 ◦ Event Storming to split Monolith into Microservices
• 2022-09-06 ◦ Common mistakes when splitting the monolith
• 2022-08-25 ◦ Design patterns for microservices - Azure Architecture Center | Microsoft Docs