What is it?

Single application built as suite of small services which have following characteristics:

• Loosely coupled 
• Communicating lightweight protocol
  • HTTP
  • REST etc
• Each running as independent processes
• Separately written, deployed, scaled

Is it SOA?

Not SOA, you can say a variant of SOA. SOA: talks about integrating various enterprise applications.

Microservices: decomposing single application into suite of smaller applications.

What are Monolithic Applications?

Consider you have a E-commerce application with following functionalities:

• Searching
• Product Catalog
• Inventory management
• Shopping cart
• Payment Management
• User Management
• Order Management
• Checkout

Now if you create it as a monolithic application, you will create a single service (app) that provides all the required functionalities.

Ok, so what are the disadvantages of the Monolithic?

Here are few disadvantages:

• Locked to technology/language
  • An entire app is written with a single tech stack, hence changing the tech stack will become a big task
  • Cannot experiment/take advantage of emerging technologies, you are stuck with the initial tech you use.
• Difficult for a single developer to understand complete code
• Generally, a big team is working on the entire app, hence you will have to deal with numerous issues during merges and merge conflicts.
• The single app is generally connecting to multiple databases, loaded with validations and business logics, hence becoming complex.
• Changes of one functionality are held back by other changes.
  • You can’t release your changes till other functionalities are done and tested.
  • If there is a bug in other functionality, you can’t release your functionality.

Are there any advantages of Monolithic applications?

Well yes.

• Easy to test as a single unit.
• Easy to deploy as a single unit.
• Easy to scale.
• Easy to manage changes.
• Easy to manage versions.

How will you create the same e-commerce app in the Microservices world?

What are advantages of micro-services?

• Faster Delivery: 
  • Less code to change
  • Less code to test
  • Easy deployment steps
• Scaling:  
  • We can scale individual services based on their use
• Easily understood: 
  • Since microservice size is small, a person or team can easily understand in and out of microservice
• Technology/language advantage
  • Different process different technology
  • If we have to change tech or language from java to python, it is small module for which we have to change
• Change cycle decoupled
  • Each functionality or micro-service can be deployed when
• Culture: Well defined ownership, hight trust in team
• Easy deployment steps
• Isolation: Single microservice cannot crash entire system
• Flexibility: Polygot services, own persistence system etc

Are there any challenges of micro-services?

You have to take care of:

• So many services to manage.
• More monitoring required.
• Design for failures
• Remote calls vs in process call speed
• Transactions which goes over multiple services
• Sometimes features spans multiple services
• Multiple services required to be tested together
• Version management