ECONNREFUSED for Postgres on nodeJS with dockers

Your DATABASE_URL refers to 127.0.0.1, which is the loopback adapter (more here). This means "connect to myself".

When running both applications (without using Docker) on the same host, they are both addressable on the same adapter (also known as localhost).

When running both applications in containers they are not both on localhost as before. Instead you need to point the web container to the db container's IP address on the docker0 adapter - which docker-compose sets for you.

Change:

127.0.0.1 to CONTAINER_NAME (e.g. db)

Example:

DATABASE_URL: postgres://username:pgpassword@127.0.0.1:5432/mydatabase

to

DATABASE_URL: postgres://username:pgpassword@db:5432/mydatabase

This works thanks to Docker links: the web container has a file (/etc/hosts) with a db entry pointing to the IP that the db container is on. This is the first place a system (in this case, the container) will look when trying to resolve hostnames.

For further readers, if you're using Docker desktop for Mac use host.docker.internal instead of localhost or 127.0.0.1 as it's suggested in the doc. I came across same connection refused... problem. Backend api-service couldn't connect to postgres using localhost/127.0.0.1. Below is my docker-compose.yml and environment variables as a reference:

version: "2"services:  api:    container_name: "be"    image: <image_name>:latest    ports:      - "8000:8000"    environment:      DB_HOST: host.docker.internal      DB_USER: <your_user>      DB_PASS: <your_pass>    networks:       - mynw  db:    container_name: "psql"    image: postgres    ports:      - "5432:5432"    environment:      POSTGRES_DB: <your_postgres_db_name>      POSTGRES_USER: <your_postgres_user>      POSTGRES_PASS: <your_postgres_pass>    volumes:      - ~/dbdata:/var/lib/postgresql/data    networks:      - mynw

If you send database vars separately. You can assign a database host.

DB_HOST=<POSTGRES_SERVICE_NAME> #in your case "db" from docker-compose file.