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This repo represents a NestJS Microservice architecture implemented using monorepo pattern.

Running the project

in order to run the project you need to:

• make a copy of .env.example file, name it .env and use your environment specific values. you'll need a running mongodb server & rabbitmq broker, you can run the rabbitmq server usually using this command:

  rabbitmq-server.bat

• execute the following command in the root directory to install the packages

  npm install

  • or use your preferred package manager.

• start the projects using the following commands:

  npm run ms1:start

  npm run ms2: start

  npm run start

  the third command starts the 3rd microservice without the need to specify its name since it's the main project.

Microservice 1 (Event Publisher)

The only module in this microservice imports the RabbitMQModule from @golevelup/nestjs-rabbitmq package and loads it with the shared configuration imported from the common libs which will be explained in the upcoming parts.

In the rabbit.service file you'll find publish function which emits an event every second to the rabbitmq broker using the publish function from the amqpConnection instance with the shared configuration imported from the common libs.

It extends the OnModuleInit to run the function as soon as the service is initialized.

Microservice 2 (Event Receiver & Data Provider)

The db.module file imports the same RabbitMQModule that was imported in microservice-1, it also imports the MongooseModule from @nestjs/mongoose and initializes them.

This microservice acts as a data provider, it contains a message schema that persists the event data.

The db.service file contains two functions:

1. handler function which is decorated with @RabbitSubscribe decorator from @golevelup/nestjs-rabbitmq with the same configuration used in the publish function in microservice-1, and specifying a queue name to support the Horizontal Scaling.

   • By specifying the queue name, We guarantee that all instances will share the same queue, resulting in handling each event in only one subscriber and inserting the event only once to the DB.

2. rpcHandler function which exposes an RPC to fetch the most recent 10 events from the DB, using a shared configuration.

Microservice 3 (Event Receiver & API)

This microservice has 2 responsibilities that are shown in the events.service file:

• The handler function accepts the events published by the first microservice and logs it to the console.

  • this function is decorated with @RabbitSubscribe, the same decorator used in the second microservice.
  • this decorator didn't specify a queue name, taking in consideration the @golevelup/nestjs-rabbitmq gives a unique queue name for each subscriber, so it won't interfere with the subscriber in the second microservice.

• The getLast10Events function makes a request to the second microservice using the request function from AmqpConnection class, using the same configuration that was specified in the rpcHandler function in the second microservice.

  • This function is used in the events.controller file which exposes an API to be used in http requests to fetch the most recent 10 events from the DB.
  • To test the API, make a GET request to events/last10.

Libs

This directory is intended to have all the common behaviors and constants that is shared across all projects.

rabbitmq directory

This directory shares this common constants and interfaces:

1. rabbitMQConfig: the configurations used to connect to RabbitMQ broker.
2. rabbitSubscribeOptions: the configurations used in publishing and receiving events.
3. rabbitRPCOptions: the configurations used in RPC request.
4. MessageInterface: an interface that represents the event.