NodeJS Cannot Connect to Postgres at Dockerized Environment - node.js

Question

I am trying to run a NodeJS application on Docker. However I get that error:
could not connect to postgres: Error: connect ECONNREFUSED
When I debug the problem I can see that my environment file is considered from the application and I can access the application endpoints until it tries to connect database.
What can be the reason?
This is my docker-compose.yml file:
version: "3.8"
services:
postgres:
image:postgres:12.4
restart: always
environment:
POSTGRES_USER: workflow
POSTGRES_DB: workflow
POSTGRES_PASSWORD: pass
ports:
- "5429:5432"
expose:
- 5429
networks:
- db
workflow:
image:workflow:0.1.0-SNAPSHOT
environment:
NODE_ENV: prod
env_file:
- ./.env.prod
logging:
driver: "json-file"
options:
max-size: "10m"
max-file: "3"
ports:
- "3000:3000"
networks:
- db
depends_on:
- postgres
networks:
db:
volumes:
db-data:
This is my Dockerfile:
FROM node:16.14.2
WORKDIR /app
COPY ["package.json", "package-lock.json*", "./"]
RUN npm ci --only=production && npm cache clean --force
COPY . .
CMD [ "npm", "run", "start"]
This is .env.prod file:
PORT=3000
DATABASE_URL=postgresql://workflow:pass#postgres:5429/workflow
Here is the related script from package.json:
"scripts": {
"start": "npm run migrate up && node src/app.js"
}
This is error output:
workflow_1 | Error: connect ECONNREFUSED 172.21.0.2:5429
workflow_1 | at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1157:16) {
workflow_1 | errno: -111,
workflow_1 | code: 'ECONNREFUSED',
workflow_1 | syscall: 'connect',
workflow_1 | address: '172.21.0.2',
workflow_1 | port: 5429
workflow_1 | }
This is from docker ps command:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c8971741b19d postgres:12.4 "docker-entrypoint.s…" 50 seconds ago Up 49 seconds 5429/tcp, 0.0.0.0:5429->5432/tcp workflow_postgres_1

Answer 1

Based on the official Dockerfile of the postgres:12.4 database it exposes default port 5432. So unless you changed that port with the pg configuration your application needs to connect to port 5432, not the 5429.
Also based on your
ports:
- "5429:5432"
section of the docker compose. If you go to the official documentation it is
ports (HOST:CONTAINER)
for the syntax. So you are technically mapping port 5429 to the "outside/host" port. Meanwhile all the internal docker traffic still goes to the port 5432.