adding index.php file for 3 tier app

index.php

+<?php
+$servername = "db";
+$username = "root";
+$password = "Qwerty123";
+$dbname = "message";
+
+// Create connection
+$conn = new mysqli($servername, $username, $password, $dbname);
+// Check connection
+if ($conn->connect_error) {
+  die("Connection failed: " . $conn->connect_error);
+}
+
+$sql = "SELECT id, message, reg_date FROM message";
+$result = $conn->query($sql);
+
+if ($result->num_rows > 0) {
+  // output data of each row
+  while($row = $result->fetch_assoc()) {
+    echo "id: " . $row["id"]. " - Message: " . $row["message"]. " " . $row["reg_date"]. "<br>";
+  }
+} else {
+  echo "0 results";
+}
+$conn->close();
+?>