Running Multiple Microservices with multiple docker compose with NATS - docker

Question

I am new to microservices and I have a project to setup multiple microservies, The project is setup like this.
Every nest js application has
API Application exposed to a port
database
docker-compose file responsible which creates the containers for each microservice.
Now what I am doing is to have
Nest JS MICROSERVICE APP 1
- API exposed to port 5000
- Postgres database working on 5432
- NATS running on 4222
NEST JS APP MICROSERVICE 2
- API exposed to port 5001
- Postgres database working on 5433
- NATS not running on 4222 as it is already occupied. If I change the port how I am gonna use the same message broker on both services.
The problem is I wanted to use the same NATS message broker on the second microservice and all the newly created microservice. my docker-compose file for NEST JS APP 1 is as follows.
version: '3.9'
services:
api:
container_name: nest_app_1
image: nest_app_1
build:
dockerfile: Dockerfile
context: .
ports:
- 127.0.0.1:5000:5000
env_file:
- .env
depends_on:
- db
- nats
networks:
- main
db:
container_name: postgres
image: postgres:latest
ports:
- 127.0.0.1:5432:5432
volumes:
- ./data:/var/lib/postgresql/data
env_file:
- .env
networks:
- main
pgadmin:
container_name: pgadmin
image: dpage/pgadmin4
ports:
- 127.0.0.1:8080:80
env_file:
- .env
networks:
- main
nats:
image: nats-streaming:latest
entrypoint:
- /nats-streaming-server
- -cid
- main_cluster
ports:
- "127.0.0.1:4222:4222"
- "127.0.0.1:6222:6222"
- "127.0.0.1:8222:8222"
restart: always
tty: true
networks:
- main
networks:
main:
driver: bridge
Second NEST JS microservice docker-compose is as follows
version: '3.9'
services:
api:
container_name: nest_app_2
image: nest_app_2
build:
dockerfile: Dockerfile
context: .
ports:
- 127.0.0.1:5001:5001
env_file:
- .env
depends_on:
- app_db_2
networks:
- main
app_db_2:
container_name: postgres_2
image: postgres:latest
ports:
- 127.0.0.1:5433:5432
volumes:
- ./data:/var/lib/postgresql/data
env_file:
- .env
networks:
- main
pgadmin:
container_name: pgadmin_2
image: dpage/pgadmin4
ports:
- 127.0.0.1:8081:80
env_file:
- .env
networks:
- main
nats:
image: nats-streaming:latest
entrypoint:
- /nats-streaming-server
- -cid
- main_cluster
ports:
- "127.0.0.1:4222:4222"
restart: always
tty: true
networks:
- main
networks:
main:
driver: bridge
Now I want to use NATS to communicate between both apps. So if I publish message from microservice 1 and I subscribe that message to microservice 2 and so on.

Answer 1

yes, sure the host ports are occupied if you link it through the Host network stack. You can only have one service linked to ip:port
It looks like you trying to start two NATS instances and let them join the same NATS cluster. But maybe you need two instances for development. You just want to see messages passing through it.
Option 1: just put everything in one compose and use depends_on and the same NATS node for both services
Option 2: Use a separate compose stack to provision your NATS infrastructure and use
extrnal_links.
Option 3: Define custom network for NATS cluster where every NATS container get's own iP.
But I would start with 1.