gistfile1.txt

docker pull mongo
docker network create mongo-cluster

 docker run -d \
-p 30001:27017 \
--name mongo1 \
--net mongo-cluster \
mongo mongod --replSet mongo-set

docker run -d \
-p 30002:27017 \
--name mongo2 \
--net mongo-cluster \
mongo mongod --replSet mongo-set


docker run -d \
-p 30003:27017 \
--name mongo3 \
--net mongo-cluster \
mongo mongod --replSet mongo-set


docker exec -it mongo1 mongo

db = (new Mongo('localhost:27017')).getDB('test')

config = {
  	"_id" : "mongo-set",
  	"members" : [
  		{
  			"_id" : 0,
  			"host" : "mongo1:27017"
  		},
  		{
  			"_id" : 1,
  			"host" : "mongo2:27017"
  		},
  		{
  			"_id" : 2,
  			"host" : "mongo3:27017"
  		}
  	]
  }
  
  rs.initiate(config)
  
  mongo-set:PRIMARY>
  DONE
  
// app.js
const mongoose = require("mongoose");
const express = require("express");

const PORT = 8080;
const HOST = "0.0.0.0";

let conn_string =
  "mongodb://localhost:30003,localhost:30002,localhost:30001/test?replicaSet=mongo-set";

mongoose
  .connect(conn_string, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  })
  .catch((e) => console.log("Error: ", e));

let db = mongoose.connection;

db.on("error", console.error.bind(console, "connection error:"));

db.on("connecting", function (d) {
  console.log("Connecting");
  console.log(d);
});

db.once("open", function () {
  console.log("Connected; Open");

  const app = express();
  app.get("/", (req, res) => {
    res.send("SachinM");
  });

  app.listen(PORT, HOST);
  console.log(`Running on http://${HOST}:${PORT}`);
});


node app.js

error: MongooseError [MongooseServerSelectionError]: getaddrinfo ENOTFOUND mongo1

FIX
---

docker exec -it mongo1 mongo 

 cfg = rs.conf()
 // IP's of VM instead of IP's of Docker private Ip
 
cfg.members[0].host = "172.19.0.2:27017"
 rs.reconfig(cfg)
cfg.members[1].host = "172.19.0.3:27017"
 rs.reconfig(cfg)
cfg.members[2].host = "172.19.0.4:27017"
 rs.reconfig(cfg)
 
 rs.reconfig(cfg)

---
node app.js

it works now.