Dockerized Python Web Application Can't Connect to PostgreSQL Database: Connection Refused Error

I am trying to set up a Docker environment for my Python web application. I have configured Nginx as a reverse proxy, Gunicorn as a WSGI HTTP server, and I’m using Redis for caching and PostgreSQL as my database. I’ve also tried to implement load balancing with Nginx and I’m using Docker Compose for orchestrating all these services.

Everything seemed to be configured correctly, but when I try to run the application, I’m experiencing an issue where my application isn’t communicating with the PostgreSQL database. The application logs are indicating a connection error. Here’s the error I’m seeing:

psycopg2.OperationalError: could not connect to server: Connection refused Is the server running on host "db" (172.20.0.2) and accepting TCP/IP connections on port 5432?

I’ve checked my Docker Compose file and everything seems to be in order. Here’s a part of my docker-compose.yml:

version: '3'
services:
  db:
    image: postgres
    volumes:
      - ./data/db:/var/lib/postgresql/data
    environment:
      POSTGRES_DB: mydb
      POSTGRES_USER: myuser
      POSTGRES_PASSWORD: mypassword

  web:
    build: .
    command: gunicorn myapp:app -c ./gunicorn_config.py
    volumes:
      - .:/code
    ports:
      - "8000:8000"
    depends_on:
      - db

And this is how I’m trying to connect to the database in my Python application:

import psycopg2
conn = psycopg2.connect(
    dbname="mydb",
    user="myuser",
    password="mypassword",
    host="db"
)

I can’t figure out what I’m doing wrong. Any ideas why the application is unable to connect to the PostgreSQL database?