section.01.md

Fundamental Ideas Around Microservices

• what is microservices

  1. A microservice should be self contained
  2. To reduce the crashes chance brought by dependencies between services, we introduced the event bus.
  3. Brought data duplication and understanding obstacle

It contains all the stuff that works one feature correctly.

• Data in microservice
  • Each service gets its database(if it needs one) for the following reasons[Database-Per-Service pattern]

    1. We want every service to be able to act independently without depending on any service
    2. If each service has its database, we can optimize what type of database we pick
    3. A single database shared between many services would be a single point of failure
    4. The data schema of a database might be changed unexpectly

  • Services will never, never reach into another service's database

Managing data between different services is a challenge.

• Big problem with data in services

  • We don't allow services to interact with databases that not owned by it directly

• communication strategies between services to solve data management in microservices

  1. Sync Services communicate with each other using direct requests
     1. Upside:
     • easy to understand
     • don't need a database
     2. downside
        • Introduce an dependency between services
        • If any inter-service request fails, the overall request fails
        • The entire request is only as fast as the slowest request
        • can easily introduce webs of request
  2. Async Services communicate with each other using events.

• Communiation using Event bus

  • The event flow:
    • Service D emit event data {type: UserQuery, data: {id}}
    • Service A(the UserService) emit data {type: UserQueryResult, data: {id, name: 'jill'}}
    • The order and the product purchase services handle the purchase and order information based on user id
  • Still has the downside mentioned in synchronouse communication way

• A crazy way of storing data

Define the service's goal ==> Define the service's data schema ==> define the event flow for services

• For service D, the goal is

  Given the ID of a user, show the title and image for every product they have erver ordered

  • pros and cons Nowdays, data storage is cheaper

Summary

Define the service's goal ==> Define the service's data schema ==> define the event flow for services

• Define the goal for services
• Reduce dependency chances by data duplication and using event bus
• microservice should be self contained and never, never reach database of another service.