jeffreyquan/nest-microservices

Example application of microservices in Nest + Kafka

Nest Microservices

This is a simple example of microservices in Nest with Kafka. Both are designed as Hybrid applications i.e. listen to HTTP requests and make use of connected microservices.

We have two services:

• User Service
• Registration Service

The example demonstrates the following flow:

1. User is created in the User Service with a name and age.

This can be done via Postman with a POST request to http://localhost:3000/api/users and a JSON body including name and age.

{
    "name": "Goku",
    "age": 88
}

2. The event user.registration.pending is emitted with the user data.
3. Registration Service listens to the user.registration.pending event and handles the user data.
4. User's age is assessed. If the user is 18 or over, the registration status is approved. Otherwise, the status is rejected. Note: the age chosen and this assessment is arbitrary
5. A registration is created and the registration ID and status is emitted with the event user.registration.fulfilled.
6. The User Service listens to the user.registration.fulfilled event and updates the user's registration status in the database.

Installation

# user-service folder and registration-service folder

npm install

Environmental Variables

# Create .env files using the .env.example files as a template

# Make sure the POSTGRES_USER, POSTGRES_PASSWORD AND POSTGRES_DB is the same across all three .env files
# If you are running Postgres locally, comment out the postgres-db service in the docker-compose.yml file

# root
POSTGRES_USER=
POSTGRES_PASSWORD=
POSTGRES_DB=

# user-service folder
POSTGRES_USER=
POSTGRES_PASSWORD=
POSTGRES_DB=
POSTGRES_PORT=5432
POSTGRES_HOST=localhost

# registration-service folder
POSTGRES_USER=
POSTGRES_PASSWORD=
POSTGRES_DB=
POSTGRES_PORT=5432
POSTGRES_HOST=localhost

Running the app

# To run Postgres, Kafka and Zooper

# root

docker-compose up

# user-service

npm run start:dev

# registration-service

npm run start:dev

Stopping docker containers

docker-compose down

Known Issues

Sometimes when starting the docker containers, the Kafka and Zookeeper services terminate referencing the error: Error:KeeperErrorCode = NodeExists. This prevents the user and registration services from connecting to Kafka. I would appreciate any help to fix this.

Alternatively, you can run Kafka and Zookeeper locally following the instructions from the Kafka Quickstart Guide.