Microservices

Communication between services

• Sync: direct requests
• Plain http requests with json exchange format
• Can create a big web of dependencies between services
• Async: communication using events
• Services emit and receive events to/from a Event Bus
• Has data duplication!
• The Query Service is responsible for the Event Bus (Event Broker)

Error handling middleware

• A function to handle all throw new Error('') along the code
• A class is created for each error type and extends the 'Error' class
• Error structure:

{
  "errors": [
    {
      "message": "Database error",
      "field": "field"
    },
    {
      "message": "Validation error"
    }
  ]
}

export abstract class CustomError extends Error {
  abstract statusCode: number;

  constructor() {
    super(); // Invoke the constructor of the Error class
    Object.setPrototypeOf(this, CustomError.prototype); // setPrototypeOf must be called when extending a built in class
  }

  abstract serializeErrors(): { message: string; field?: string }[];
}

Authentication strategies

• Tokens: JWT, Cookie, etc

• Option 1:

• "order" service always ask "auth" service

• "auth" service checks if the token is valid and the user is authenticated

• "auth" sends the response back to "order" directly (not through event bus

• Option 2:

• "order" has all the logic to validate a token

• "order" doesn't need to reach auth service
• user could be banned and the auth service could not tell the order

• A "ban event" could also be emitted b the auth service

• JWT

• Request: Authorization (header), token (body), Cookie (header)

• A payload is transformed in a jwt string by means of a secret key

• the jwt is decoded by the server

• Cookie

• Request: Cookie: 'blabla'
• Response: Set-Cookie: 'blabla'
• Server emitts a Set-Cookie and the Client stores it in the browser
• The Cookie is sent back by the Client when it makes a new request

Server-side render

• Browser make request to an back-end server (NextJS)
• NextJS build the html for the entire app by requesting other services
• NextJS sends back to browser fully rendered pure HTML
• Boost the page load speed
• With server-side rendering, NextJS must know auth info with the first request
• Auth info MUST be passed as a Cookie (with jwt inside) with server-side rendering

Cross Service data replication

Embedding strategy

• Strategy to associate a internal model to another external model from another service
• A property of the internal model receives a whole document of the external model

Ref/Population Feature

• Populates an external model to inside of a property
• Two separate collections

Optimistic Concurrency Control

• Add a version to any document in the database
• Each update will be made considering the previous version
• If the version is not the desired, the update will hang
• 'mongoose-update-if-current' module
• The version number should only be incremented in the service that primarily stores it

Scheduled event

• The event will only be redistributed by the event bus after some time window
• Not supported by nats
• BullJS library handles timing notifications

Worker server

• A independent standalone service that process demanding actions
• Example: a video file conversion is process demanding and takes time
• That way, the original service is free to perform other activities
• A Job is the unit for the action to be processed by the worker
• BullJS handles the jobs in the worker

Payment handling

• Stripe handle credit card payment
• A token is created and with that the payment is sent to stripe API
• default test token tok_visa

Hosting providers

• Digital Ocean
• AWS
• Google Cloud
• Azure

Further development

• HTTPS support
• cert-manager.io
• Email support
• Mailchimp/Sendgrid
• Production dockerfile and K8S config files
• Production files adding the build step
• Staging cluster
• Cluster for testing on Digital Ocean