react-express-mongodb: rename server to backend

The goal here is to keep the same structure than the other examples.
Also, considering that it has a "frontend" folder, the equivalent for
the server should be "backend".

Signed-off-by: Jérémie Drouet <jeremie.drouet@gmail.com>

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

@@ -0,0 +1,30 @@
+/**
+ * Created by Syed Afzal
+ */
+const mongoose = require('mongoose');
+const {log} = require('../utils/helpers/logger');
+
+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();
+};