Django + Docker: connection to server at "localhost" (127.0.0.1), port 5432 failed

I am trying to run my Django app (Nginx, Gunicorn) in docker.

But for request http://167.99.137.32/admin/ I have error: (full log https://pastebin.com/0f8CqCQM)

onnection to server at "localhost" (127.0.0.1), port 5432 failed: Connection refused
    Is the server running on that host and accepting TCP/IP connections?
connection to server at "localhost" (::1), port 5432 failed: Address not available
    Is the server running on that host and accepting TCP/IP connections?

I was trying answers from Can't run the server on Django (connection refused) but didn't solve my problem

settings.py

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'lk_potok_2',
        'USER': 'postgres',
        'PASSWORD': 'post222',
        'HOST': 'localhost',
        'PORT': 5432,
    },

docker-compose.yml

version: '3.9'

services:
  django:
    build: . # path to Dockerfile
    command: sh -c "gunicorn --bind 0.0.0.0:8000 potok.wsgi:application"
    volumes:
      - .:/project
      - static:/project/static
    expose:
      - 8000
    environment:
      - DATABASE_URL=postgres://postgres:post222@localhost:5432/lk_potok_2"
      - DEBUG=1

  db:
    image: postgres:13-alpine
    volumes:
      - pg_data:/var/lib/postgresql/data/
    expose:
      - 5432
    environment:
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=post222
      - POSTGRES_DB=lk_potok_2

  nginx:
    image: nginx:1.19.8-alpine
    depends_on:
      - django
    ports:
      - "80:80"
    volumes:
      - static:/var/www/html/static
      - ./nginx-conf.d/:/etc/nginx/conf.d

volumes:
    pg_data:
    static:

nginx-conf.nginx

upstream app {
    server django:8000;
}

server {
    listen 80;
    server_name 167.99.137.32;

    location / {
        proxy_pass http://django:8000;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;
        proxy_redirect off;
    }

    location /static/ {
        alias /var/www/html/static/;
    }
}

I was trying sudo systemctl start postgresql and sudo systemctl enable postgresql (the same error)

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'lk_potok_2',
        'USER': 'postgres',
        'PASSWORD': 'post222',
        'HOST': 'db',
        'PORT': 5432,
    },

environment:
      - DATABASE_URL=postgres://postgres:post222@localhost:5432/lk_potok_2"