orders-payments-microservices

An example project demonstrating event sourcing and Command Query Responsibility Segregation (CQRS) using a couple of NestJS microservices with an Angular frontend app. Redis is used as a read database and also acts as the message broker for the pub/sub communication between the microservices. All the events are persisted into a MongoDB database.

CQRS Pattern

Description

orders

• Responsible for the management of orders
• Each order can only be at a single state at a time
• Order states: created, confirmed, delivered, cancelled
• Once an order is created, the orders app publishes an event which is subscribed by the payments app to process a payment for the order
• If the payment of the order is declined, the order is set to cancelled
• If the payment of the order is confirmed, the order is set to confirmed
  • After X amount of seconds a confirmed order is automatically set to delivered
• Has endpoints to do the following:
  1. view all orders
  2. create an order
  3. cancel an order
  4. check order status

payments

• Responsible for payment processing
• Each order is handled by the payments app by setting the payment of the order to confirmed or declined based on random logic
• Each payment is persisted into its own table in the MongoDB database
• Once a payment is processed, the payments app publishes an event which is subscribed by the orders app to continue with order processing

portal

• A user of the portal app can do the following:
  1. view list of orders
  2. view the details of an order
  3. create an order
  4. cancel an order
• Login requires a Gmail account for auth
• Implements server-sent events (SSE) to update the state of an order

Order event flow

• Events that are stored in the event store are highlighted in red
• The dotted green lines represent pub/sub messaging via Redis

How To Run

Prerequisites

• It is assumed that the user has a basic understanding of Kubernetes and Helm charts
• A Firebase developer account is required to handle auth for the portal and orders app
• Installation scripts available for Minikube and Google Cloud Platform
  • Please ensure to copy the file .firebase-configmap.example.yaml and set the values accordingly prior to starting installation.

  $ cp firebase-configmap.example.yaml firebase-configmap.yaml
  

Install on Minikube

Open a shell and run these commands:

$ minikube start
$ cd orders-payments-microservices/helm/scripts
$ ./install.sh

Install on Google Cloud Platform

Open a shell and run these commands:

$ gcloud auth login
$ cd orders-payments-microservices/helm/scripts
$ ./gcloud_add_helm.sh
$ ./gcloud_startup.sh
$ ./install.sh

Install on local machine

Set the configuration values / enviroment variable of each application.

orders / payments

Copy the file .env.example and set each environment variable accordingly.

$ cp .env.example .env

portal

Set the configuration values in the EnvService class.

export class EnvService {
  // The values that are defined here are the default values that can
  // be overridden by the generated env.js file.

  public production = false;
  public ordersURL = '';
  public apiKey = '';
  ...

Note: the env.js file is only generated when installation is made on a Kubernetes cluster.

Add IP/domain to Firebase console

Once installation is done, please ensure to whitelist the IP/domain in the Firebase console as shown below.

Reconstruct view

The materialized view can be reconstructed by opening a shell to the orders pod and running the script below.

# npm run reconstruct-view-db

Working Example

A working example of the demo project can be found here.