django.db.utils.OperationalError: connection to server failed. FATAL: password authentication failed for user "root"

I'm running Django rest api with the django 3.2 on GCPUbuntu 22.04 LTS and docker. I switched my database engine to postgresql from mysql (Read that for large scale operations, PostgreSQL is most suitable). I'm getting the following password authentication error when I run my containers.

django.db.utils.OperationalError: connection to server at "db.earthling" (172.16.16.4), port 5432 failed: FATAL: password authentication failed for user "root"

which comes from :

psycopg2.OperationalError:onnection to server at "db.earthling" (172.16.16.4), port 5432 failed: FATAL: password authentication failed for user "root" DETAIL: Role "root" does not exist DETAIL: Role "root" does not exist

There is also a similar error :

/usr/local/lib/python3.8/site-packages/django/core/management/commands/makemigrations.py:105: RuntimeWarning: Got an error checking a consistent migration history performed for database connection 'default': connection to server at "db.earthling" (172.16.16.4), port 5432 failed: FATAL: password authentication failed for user "root"

Howvever, I have placed the POSTGRE_PASSWORD in environment files. Here are the details:

.docker-compose.env which points to the relevant variables
# [GROUP] POSTGRESQL Database Configuration
# [DESCRIPTION] The SQL database configuration
# [REQUIRED][ALWAYS]
RDS_DB_NAME=earthling
RDS_USERNAME=root
RDS_HOSTNAME=db.earthling
RDS_PORT=5432
RDS_HOSTNAME_READER=db.earthling
RDS_HOSTNAME_WRITER=db.earthling
#[NAME] RDS_PASSWORD
# [DESCRIPTION] The password for the PostgreSQL Database. If using earthling-cli, obtained from .earthling-cli.json
RDS_PASSWORD=Long password here
POSTGRES_PASSWORD=Same as RDS_PASSWORD

.env file which points to the relevant variables

# [GROUP] POSTGRESQL Database Configuration
# [DESCRIPTION] The SQL database configuration
# [REQUIRED][ALWAYS]
RDS_DB_NAME=earthling
RDS_USERNAME=root
RDS_HOSTNAME=172.16.16.4
RDS_PORT=5433
RDS_HOSTNAME_READER=172.16.16.4
RDS_HOSTNAME_WRITER=172.16.16.4
# [NAME] RDS_PASSWORD
# [DESCRIPTION] The password for the SQL Database.
RDS_PASSWORD=Long password here
POSTGRES_PASSWORD=Same as RDS_PASSWORD

Here is my settings.py that points to the database engine change:

if IS_BUILD or TESTING:
    DATABASES = {
        'default': {
            # 'ENGINE': 'django.db.backends.mysql',
            'ENGINE' :'django.db.backends.postgresql',
            'NAME': 'earthling-api'
        }
    }
else:
    RDS_DB_NAME = os.environ.get('RDS_DB_NAME')
    RDS_USERNAME = os.environ.get('RDS_USERNAME')
    RDS_PASSWORD = os.environ.get('RDS_PASSWORD')
    RDS_PORT = os.environ.get('RDS_PORT')
    RDS_HOSTNAME = os.environ.get('RDS_HOSTNAME')

    RDS_HOSTNAME_WRITER = os.environ.get('RDS_HOSTNAME_WRITER', RDS_HOSTNAME)
    RDS_HOSTNAME_READER = os.environ.get('RDS_HOSTNAME_READER', RDS_HOSTNAME_WRITER)

    # db_options = {
    #     'init_command': "SET sql_mode='STRICT_TRANS_TABLES'",
    #     'charset': 'utf8mb4'
    # }

    writer_db_config = {
        # 'ENGINE': 'django.db.backends.mysql',
        'ENGINE' :'django.db.backends.postgresql',
        'NAME': RDS_DB_NAME,
        'USER': RDS_USERNAME,
        'PASSWORD': RDS_PASSWORD,
        'HOST': RDS_HOSTNAME_WRITER,
        'PORT': RDS_PORT,
        # 'OPTIONS': db_options,
    }

    DATABASES = {
        'default': writer_db_config,
        'Reader': {
            # 'ENGINE': 'django.db.backends.mysql',
            'ENGINE' :'django.db.backends.postgresql',
            'NAME': RDS_DB_NAME,
            'USER': RDS_USERNAME,
            'PASSWORD': RDS_PASSWORD,
            'HOST': RDS_HOSTNAME_READER,
            'PORT': RDS_PORT,
            # 'OPTIONS': db_options,
            'ATOMIC_REQUESTS': True,
        }
    }

    DATABASE_ROUTERS = ['django_replicated.router.ReplicationRouter']

My docker-compose.yml :

version: '3'

services:
  webserver:
    container_name: my-api-webserver
    build:
      dockerfile: Dockerfile
      context: ./.docker/api
    privileged: true
    extra_hosts:
      - db.earthling:172.16.16.4
      - redis.earthling:172.16.16.5
    volumes:
      - ./:/opt/earthling-api
      - ./.docker-cache/pip:/root/.cache/pip
    ports:
      - 80:80
    working_dir: /opt/earthling-api
    networks:
      earthling:
        ipv4_address: 172.16.16.1
    depends_on:
      - db
      - redis
    env_file:
      - .docker-compose.env
  
  db:
    container_name: earthling-postgresql-database
    image: postgres:latest
    hostname: db.earthling
    volumes:
      - postgresdb:/var/lib/postgresql
    ports:
      - 5432
    privileged: false
    networks:
      earthling:
        ipv4_address: 172.16.16.4
    # command: --character-set-server=utf8 --collation-server=utf8_unicode_ci
    env_file:
      - .docker-compose.env
  

 
volumes:
  postgresdb:
  redisdb:

networks:
  earthling:
    ipam:
      driver: default
      config:
        - subnet: "172.16.16.0/16"

My webserver docker file :

FROM python:3.8.14

RUN apt-get -y update && apt-get -y upgrade && apt-get install -y ffmpeg 
COPY wait-for-it.sh /wait-for-it.sh

# Copy any files over
COPY entrypoint.sh /entrypoint.sh

# Copy any files over
COPY bootstrap_development_data.sh /bootstrap_development_data.sh

# Change permissions
RUN chmod +x /entrypoint.sh
RUN chmod +x /bootstrap_development_data.sh
RUN chmod +x /wait-for-it.sh
RUN groupadd -r docker && useradd -r -g docker earthling


ENTRYPOINT ["/entrypoint.sh"]

COPY requirements.txt /requirements.txt
RUN pip3 install --upgrade pip setuptools wheel
RUN pip3 install -r /requirements.txt
RUN yes | pip uninstall django-rq-scheduler
RUN yes | pip install -U django-rq-scheduler


VOLUME ["/opt/earthling-api"]

EXPOSE 80

CMD ["python", "manage.py", "runserver", "0.0.0.0:80"]

# Change permissions
RUN chown -R earthling:docker /root/.cache/pip

I'm definitely missing something OR there is something wrong in the manner in which I am setting up. Help appreciated.