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Section 1 - Fundamental Ideas Around Microservices

4. What Is a Microservice?

  • Monolithic server contains
    • Routhing, Middlewares, Business Logic, Database Access
    • to implement all featrues of our app
  • A single microservice contains
    • Routhing, Middlewares, Business Logic, Database Access
    • to implement one feature of our app

5. Data in Microservices

  • Database-Per-Service Pattern
    • Each service will have its own data (if it needs)

6. Big Problems with Data

Data management between services

This is the big problem of microservices, and what 90% of this course focuses on

7. Sync Communication Between Services

  • Sync: Services communicate with each other using direct requests
  • Async: Services communicate with each other using events

These words don't mean what they mean in the Javascript world!!!!

  • Sync - Pros
    • Conceptually easy to understand
    • Service D won't need a database
  • Sync - Cons
    • Introduces a 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 requests

8. Event-Based Communication

  • Async method #1: works the same as Sync but via Event Bus
    • So, the Pros and Cons are the same as Sync way.

10. Pros and Cons of Async Communication

Just like the database-per-service pattern, async communication is going to seem bizarre and inefficient

  • Pros
    • Service D has zaro dependencies on other services.
    • Service D will be extremely fast.
  • Cons
    • Data duplication (but it won't cost too much)
    • Harder to understand

Section 2 - A Mini-Microservices App

13. Project Setup

mkdir blog
cd blog
npx create-react-app client
# ./blog/
mkdir posts
cd posts
npm init -y
npm install --save express cors axios nodemon
# ./blog/
mkdir comments
cd comments
npm init -y
npm install --save express cors axios nodemon

14. Posts Service Creation

// blog/posts/index.js
// generate simple id
const { randomBytes } = require('crypto');
const id = randomBytes(4).toString('hex');

15. Testing the Posts Service

  • Postman POST test
    • POST / localhost:4000/posts
    • Headers: Content-Type: application/json
    • Body: raw / JSON
      • { "title": "First Post" }
  • Postman GET test
    • GET / localhost:4000/posts
    • Headers: Content-Type: application/json

20. React Project Setup

# blog/client
npm install --save axios
// settings.json
// Enabling to use emmet in JSX
{
  "emmet.includeLanguages": {
    "javascript": "javascriptreact"
  }
}

27. Request Minimization Strategies

The problem so far, is that the front server is requesting too many http requests
to get posts and comments

It would not be a problem with a monoliths service!

How to solve it with microservices?

  1. Solution #1 - Sync communication
    • when get posts - take the whole bunch of data including comments
  2. Solution #2 - Async communication
    • using Event Broker (Event bus?)
    • and using a new service: Query service

28. An Async Solution

  • Pros
    • Query Service has zaro dependencies on other services.
    • Query Service will be extremely fast.
  • Cons
    • Data duplication (but it won't cost too much)
    • Harder to understand

30. Event Bus Overview

  • Many different implementations.
    • RabbitMQ
    • Kafka
    • MATS
    • ZeroMQ
  • Receives events, publishes them to listeners
  • Many different subtle features that make async communication way easier or way harder
  • We are going to build our own event bus using Express. It will not implement the vast majority of features a normal bus has
  • Yes, for our next app we will use a production grade, open source event bus

30. Event Bus Overview

# /blog
mkdir event-bus
cd event-bus
npm init -y
npm install --save express axios nodemon

36. Creating the Data Query Service

# /blog
mkdir query
cd query
npm init -y
npm install --save express cors nodemon

38. Using the Query Service

Now, if post server or comment server is down
we still get all data from query server

40. Issues with Comment Filtering

Adding a new feature : Moderation service (if it contains 'Orange')

  • status : pending | approved | rejected
  1. Option #1 - Moderation communicates event creation to query service
    • Chain. Comment -> Event bus -> Moderation -> Event bus -> Query Service -> GUI
    • What if the Moderation Service takes very long time to process?

41. A Second Approach

  1. Option #2 - Moderation updates at both comments and query services
    • Query service instantly create { status: 'pending' } while moderation is processing

But what if the comment has various options including complex business logic

  • type: CommentModerated - comment.status = 'approved'
  • type: CommentUpvoted - comment.votes += 1
  • type: CommentDownvoted - comment.votes -= 1
  • type: CommentPromoted - comment.promoted = true
  • type: CommentAnonymized - comment.userId = null
  • type: CommentSearchable - comment.searchable = true
  • type: CommentAdvertised - comment.advertised = true

and it has more Services and they have to handle these comment status above?

  • Query Service
  • Weekly Update Service
  • Recommendation Service

42. How to Handle Resource Updates

  1. Option #3 - Query Service only listens for 'update' events
    • Comments Service will handle all complex logic and send 'CommentUpdated' to Query Service
    • Comment -> Event bus -> Moderation -> Event bus -> Comment -> Event bus -> Query Service -> GUI
    • Comment will have default status { status: 'pending' } so, if Moderation takes long time, it is okay

43. Creating the Moderation Service

# /blog
mkdir moderation
cd moderation
npm init -y
npm install --save express axios nodemon

44. Adding Comment Moderation to 48. A Quick Test

  1. Comment Service - send { type: 'CommentCreated' }, { status: 'pending' }
  2. Query Service - receive { type: 'CommentCreated' }, { status: 'pending' }
  3. Event Bus - broadcast
  4. Moderation Service - receive { type: 'CommentCreated' }, { status: 'pending' }
  5. Moderation Service - send { type: 'CommentModerated' }, { status: 'rejected' | 'approved' }
  6. Event Bus - broadcast
  7. Comment Service - receive { type: 'CommentModerated' }
  8. Comment Service - send { type: 'CommentUpdated' }
  9. Event Bus - broadcast
  10. Query Service - receive { type: 'CommentUpdated' }

49. Rendering Comments by Status

Even when moderation service is down, the system is not clashed.
But when moderation service is up, the status is still 'pending' and it's a bit unsynched situation

50. Dealing with Missing Events

  1. Option #1 - Sync Requests
    • Downside: should implement expected behaviour in Query, Posts and Comments
  2. Option #2 - Direct DB Access
    • Downside: should implement in Query Service with interfaces for different DBs
  3. *Option #3 - Store Events
    • in Event Bus

53. Event Syncing in Action

# blog/query
npm install --save axios

Holy moly... This is neat!

Section 3 - Running Services with Docker

54. Deployment Issues

Since deploying to a cloud service,

  1. Scenario #1. Comments Service is over heated, so it needs scaling up.
    • adding two more Comemnts Services
    • two more endpoints need to be handled
  2. Scenario #2. If additional Comments Services are built in the second virtual machine
  3. Scenario #3. When not busy time, we want to shut down additional Comments Services to save money and resource.

Docker and Kubernetes can be good solutions!!

56. Why Kubernetes?

  • Cluster
    • Mater: Program to manage everything in the cluster
    • Node: Virtual machine

59. Dockerizing the Posts Service

# blog/posts
docker build .
# => => writing image sha256:7058e1a2c1691c63ded015c9a13731d9e2690b8b70cc  0.0s
docker run 7058e1a2c1691c63ded015c9a13731d9e2690b8b70cc

60. Review Some Basic Commands

docker build -t pcsmomo/posts .
docker run [image id or image tag]
docker -it [image id or image tag] [cmd]
# docker run -it pcsmomo/posts sh
docker ps
docker exec -it [container id] [cmd]
# docker exec -it pcsmomo/posts sh
docker logs [container id]

61. Important Note Regarding Node v17

Currently, there is a critical bug in many libraries such as Webpack and Create React App caused by the release of Node v17.