μServices + CQRS

Pros

• Easy to develop
• Simple to test
• Simple to deploy
• Low resources mem/cpu needs

Cons

• Monoliths don’t have the capacity to handle the complexity of larger applications
• Scaling can be an issue
• Smallest change requires entire system be rebuilt and redeployed

Monolith

Pros

• Small and focused on a specific feature
• Independent deployment
• Scalability is easier
• Can be developed independently by small team
• Different language, framework
• Autonomous

Cons

• More discussion soon...

Microservice

CQRS + EventSourcing + μServices

Skype analogy

• User - μServices
• Private message - command
• Chat message - event
• Chat - event stream (write db), enterprise service bus

Example

• we have Receptionist, Librarian users in a chat
• visitors go to library to get some books (chat messages run)
• Reminder user is added to the chat (read history, make notes)
• Reminder send private message to Librarian to ban some visitors
• new rules for Remider user: make newsletter for top 10 visitors (read history again)

Don't use μServices unless you have to

• μServices inside monolith at start
• Once you cross process boundary you will get overhead:
  • Serialization cost
    
  • Request delivery cost
    
  • Failure (network, app)
    
  • Version inconsistency (previous version support)
    
  • No .net infrastructure, examples