Added somefixes

compose/app.yml

@@ -9,17 +9,17 @@ services:
     ports:
       - 127.0.0.1:3306:3306
 
-  app:
+app:
-    build: ./app
+  build: ./app
-    depends_on:
+  depends_on:
-      - db
+    - db
-    environment:
+  environment:
-      DB_HOST: 127.0.0.1
+    DB_HOST: db 
-      DB_USER: exemple
+    DB_USER: exemple
-      DB_PASSWORD: exemple
+    DB_PASSWORD: exemple
-      DB_NAME: exemple
+    DB_NAME: exemple
-    command: ["./wait-for-it.sh", "127.0.0.1:3306","--","node","index.js"]
+  command: ["./wait-for-it.sh", "db:3306", "--", "node", "index.js"] # Also change here
-    volumes:
+  volumes:
-      - ./app:/usr/src/app
+    - ./app:/usr/src/app
-    ports:
+  ports:
-      - 127.0.0.1:3000:3000
+    - 127.0.0.1:3000:3000

compose/app/index.js

@@ -1,10 +1,14 @@
 var express = require('express');
 var app = express();
 var mysql = require("mysql");
-var con = mysql.createConnection({ host: process.env.MYSQL_HOST, user: process.env.MYSQL_USER, password: process.env.MYSQL_PASSWORD, database: process.env.MYSQL_DATABASE});
+var con = mysql.createConnection({ 
+  host: process.env.DB_HOST, // Use DB_HOST instead of MYSQL_HOST
+  user: process.env.DB_USER, 
+  password: process.env.DB_PASSWORD, 
+  database: process.env.DB_NAME // Use DB_NAME instead of MYSQL_DATABASE
+});
 
 // mysql code
-
 con.connect(function(err){
   if(err){
     console.log('Error connecting to db: ', err);
@@ -18,14 +22,12 @@ con.connect(function(err){
 
 // Request handling
 app.get('/', function (req, res) {
-  // create table if not exist
+  con.query('INSERT INTO visits (ts) values (?)', Date.now(), function(err, dbRes) {
-  con.query('INSERT INTO visits (ts) values (?)', Date.now(),function(err, dbRes) {
     if(err) throw err;
-    res.send('Hello World! You are visitor number '+dbRes.insertId);
+    res.send('Hello World! You are visitor number ' + dbRes.insertId);
   });
 });
 
-
 // server
 var server = app.listen(3000, function () {
   var host = server.address().address;