MongoDB Replication Set with Configuration file and scripts in docker-compose

docker-compose.yml

version: "3"
services:
  mongo1:
    hostname: mongo1
    container_name: mongo1
    image: mongo:5.0.6
    expose:
      - 27017
    ports:
      - 27011:27017
    restart: always
    entrypoint: [ "/usr/bin/mongod", "--bind_ip_all", "--replSet", "rs0" ]
    networks:
      - replset-network
    volumes:
      - ./data/db1:/data/db
      - ./init.sh:/scripts/init.sh
  mongo2:
    hostname: mongo2
    container_name: mongo2
    image: mongo:5.0.6
    expose:
      - 27017
    ports:
      - 27012:27017
    restart: always
    entrypoint: [ "/usr/bin/mongod", "--bind_ip_all", "--replSet", "rs0" ]
    networks:
      - replset-network
    volumes:
      - ./data/db2:/data/db
  mongo3:
    hostname: mongo3
    container_name: mongo3
    image: mongo:5.0.6
    expose:
      - 27017
    ports:
      - 27013:27017
    restart: always
    networks:
      - replset-network
    entrypoint: [ "/usr/bin/mongod", "--bind_ip_all", "--replSet", "rs0" ]
    volumes:
      - ./data/db3:/data/db


networks:
  replset-network:
    driver: bridge

init.sh

#!/bin/bash

mongo <<EOF
var config = {
    "_id": "rs0",
    "version": 1,
    "members": [
        {
            "_id": 1,
            "host": "mongo1:27011",
            "priority": 1
        },
        {
            "_id": 2,
            "host": "mongo2:27012",
            "priority": 2
        },
        {
            "_id": 3,
            "host": "mongo3:27013",
            "priority": 3
        }
    ]
};
rs.initiate(config, { force: true });
rs.status();
EOF

stat_db.sh

#!/bin/bash

docker-compose --file docker-compose.yml up -d

sleep 7

docker exec mongo1 /scripts/init.sh

As there will be an election to choose which member will be PRIMARY, mongo1 has the highest chance to be the Primary server.
therefore you have to check first with one is the PRIMARY then use it in the database connection string

mongodb://localhost:27011/mydatabse?replicaSet=rs0&readPreference=primary&directConnection=true&ssl=false

localhost:27011 is the host:port of mongo1