awesome-compose/react-express-mongodb/backend/db/index.js

/**
 * Created by Syed Afzal
 */
const mongoose = require("mongoose");

exports.connect = (app) => {
  const options = {
    useNewUrlParser: true,
    autoIndex: false, // Don't build indexes
    reconnectTries: 30, // Retry up to 30 times
    reconnectInterval: 500, // Reconnect every 500ms
    poolSize: 10, // Maintain up to 10 socket connections
    // If not connected, return errors immediately rather than waiting for reconnect
    bufferMaxEntries: 0,
  };

  const connectWithRetry = () => {
    mongoose.Promise = global.Promise;
    console.log("MongoDB connection with retry");
    mongoose
      .connect(process.env.MONGODB_URI, options)
      .then(() => {
        console.log("MongoDB is connected");
        app.emit("ready");
      })
      .catch((err) => {
        console.log("MongoDB connection unsuccessful, retry after 2 seconds.");
        setTimeout(connectWithRetry, 2000);
      });
  };
  connectWithRetry();
};