I am not able to connect to my mongodb. I have used DB_CLUSTER as localhost:27017 but still getting the same error .My code is below

mongo.py

# Load environment variables
dotenv_path = "../../.env"
load_dotenv(dotenv_path)

db_user = os.getenv("DB_USERNAME")
db_pass = os.getenv("DB_PASSWORD")
db_cluster = os.getenv("DB_CLUSTER")
db_name = os.getenv("DB_NAME")

# Setting up MongoDB connection
client = MongoClient(
    f'mongodb://{db_user}:{db_pass}@{db_cluster}/?retryWrites=true&w=majority'
)

db = client[db_name]

.env 

DB_USERNAME=root
DB_PASSWORD=example
DB_CLUSTER=mongodb:27017
DB_NAME=scrapperdb

DockerCompose.yml

version: '3.8'

services:
  mongodb:
    image: mongo:latest
    container_name: mongodb
    environment:
      MONGO_INITDB_ROOT_USERNAME: ${DB_USERNAME}
      MONGO_INITDB_ROOT_PASSWORD: ${DB_PASSWORD}
      MONGO_INITDB_DATABASE: ${DB_NAME}
    ports:
      - "27017:27017"
    volumes:
      - mongo-data:/data/db

  app:
    build:
      context: .
      dockerfile: Dockerfile
    container_name: myapp
    environment:
      - DB_USERNAME=${DB_USERNAME}
      - DB_PASSWORD=${DB_PASSWORD}
      - DB_CLUSTER=${DB_CLUSTER}
      - DB_NAME=${DB_NAME}
    ports:
      - "5001:5001"
    depends_on:
      - mongodb

volumes:
  mongo-data:

I am using Docker to connect to my DB using GUI. I am not able to do it and also my application is also not able to connect to DB.