Linux, Apache, MySQL, PHP

Hi all, I'm trying to understand the following failover and clustering architecturthe, but I can not understand why on the Main server side we have 3 physicals Tomcat aplications servers and 1 physical Apache Server indicating a direct connection wiht another Apache at the Frontend? I'm confused with the architecture. Can you maybe please help me understand the infrastructure shown in att pic? Which server performs load balancing and HA?

Best regards

    Apache Frontal
      /        \
Apache1     Apache2
    |          |
TOMCAT1     TOMCAT1
    |          |
TOMCAT2     TOMCAT2
    |          |
TOMCAT3     TOMCAT3

   <?php
$sql="SELECT * FROM users WHERE id=1";
$result=$database->query($sql);
$user_found=mysqli_fetch_array($result);
echo $user_found['user name'];
    ?>

public function query($sql){
    $result= mysqli_query($this->connection, $sql);
    return $result;
}

Warning: mysqli_query() expects parameter 1 to be mysqli, null given in \ on line 19
mysqli_fetch_array() expects at least 1 parameter, 0 given in \ on line 12

any latest api for currency converter free

<pre lang="text">{
   "order":"yzaP3EQAQtCOBLhYP2ZN-Q",
   "id":"yzaP3EQAQtCOBLhYP2ZN-Q",
   "reference":"MyDomain190418-3737-54184",
   "buyerReference":null,
   "completed":true,
   "changed":1555598658633,
   "changedValue":1555598658633,
   "changedInSeconds":1555598658,
   "changedDisplay":"4/18/19",
   "language":"en",
   "live":false,
   "currency":"USD",
   "payoutCurrency":"USD",
   "invoiceUrl":"<a href="https://MyDomain.test.onfastspring.com/account/order/MyDomain190418-3737-54184/invoice">https://MyDomain.test.onfastspring.com/account/order/MyDomain190418-3737-54184/invoice</a>",
   "account":{
      "id":"qjY3pex6TH6rj6A2f71vVg",
      "account":"qjY3pex6TH6rj6A2f71vVg",
      "contact":{
         "first":"Jassim",
         "last":"Al Rahma",
         "email":"myemail@gmail.com",
         "company":null,
         "phone":"123456789"
      },
      "language":"en",
      "country":"AE",
      "lookup":{
         "global":"XNpsaeO3QLO906bY9HcusA"
      },
      "url":"<a href="https://MyDomain.test.onfastspring.com/account">https://MyDomain.test.onfastspring.com/account</a>"
   },
   "total":29.99,
   "totalDisplay":"USD 29.99",
   "totalInPayoutCurrency":29.99,
   "totalInPayoutCurrencyDisplay":"USD 29.99",
   "tax":0.0,
   "taxDisplay":"USD 0.00",
   "taxInPayoutCurrency":0.0,
   "taxInPayoutCurrencyDisplay":"USD 0.00",
   "subtotal":29.99,
   "subtotalDisplay":"USD 29.99",
   "subtotalInPayoutCurrency":29.99,
   "subtotalInPayoutCurrencyDisplay":"USD 29.99",
   "discount":0.0,
   "discountDisplay":"USD 0.00",
   "discountInPayoutCurrency":0.0,
   "discountInPayoutCurrencyDisplay":"USD 0.00",
   "discountWithTax":0.0,
   "discountWithTaxDisplay":"USD 0.00",
   "discountWithTaxInPayoutCurrency":0.0,
   "discountWithTaxInPayoutCurrencyDisplay":"USD 0.00",
   "billDescriptor":"FS* fsprg.com",
   "payment":{
      "type":"test",
      "cardEnding":"4242"
   },
   "customer":{
      "first":"Jassim",
      "last":"Al Rahma",
      "email":"myemail@gmail.com",
      "company":null,
      "phone":"123456789"
   },
   "address":{
      "country":"AE",
      "display":"AE"
   },
   "recipients":[
      {
         "recipient":{
            "first":"Jassim",
            "last":"Al Rahma",
            "email":"myemail@gmail.com",
            "company":null,
            "phone":"123456789",
            "account":{
               "id":"qjY3pex6TH6rj6A2f71vVg",
               "account":"qjY3pex6TH6rj6A2f71vVg",
               "contact":{
                  "first":"Jassim",
                  "last":"Al Rahma",
                  "email":"myemail@gmail.com",
                  "company":null,
                  "phone":"123456789"
               },
               "language":"en",
               "country":"AE",
               "lookup":{
                  "global":"XNpsaeO3QLO906bY9HcusA"
               },
               "url":"<a href="https://MyDomain.test.onfastspring.com/account">https://MyDomain.test.onfastspring.com/account</a>"
            },
            "address":{
               "country":"AE",
               "display":"AE"
            }
         }
      }
   ],
   "notes":[

   ],
   "items":[
      {
         "product":"featured-ad",
         "quantity":1,
         "display":"Featured Ad",
         "sku":null,
         "subtotal":29.99,
         "subtotalDisplay":"USD 29.99",
         "subtotalInPayoutCurrency":29.99,
         "subtotalInPayoutCurrencyDisplay":"USD 29.99",
         "discount":0.0,
         "discountDisplay":"USD 0.00",
         "discountInPayoutCurrency":0.0,
         "discountInPayoutCurrencyDisplay":"USD 0.00",
         "fulfillments":{

         }
      }
   ]
}</pre>

SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'WHERE id = 6 `Email` = 'ali@test.com' , UPDATE `users` SET `Name` = 'ali85' ' at line 1

<pre><?php
if(isset($_POST['update'])){
    $username=$_POST['Name'];
    $password = $_POST['Password'];
    $email = $_POST['Email'];
    $id = $_POST['id'];

    $query = "UPDATE `users`  SET  ";
    $query .=" `Name` = '$username' , " ;
    $query .= "  `Password` = '$password' , ";
    $query .= " `Email` = '$email' , " .
    $query .= " WHERE id = $id " ;

   $result = mysqli_query($connection , $query);
if(!$result){
    die("Query Failed". mysqli_error($connection));
}
}
?>

        <div id="d2">
            <script>
                if(document.getElementById('d2').style.display == 'block')
                {
                <?php
                    $ri = "#2 (Off-Duty Employment)";

                    ?>

            </script>
            <div id ="formular2">
                <form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
                    <div class='pl'>
                        <label>Employee Name:</label>
                        <input type="text" name="name" placeholder="Ex: John Doe" value="<?php echo $name;?>">
                        <label>Employee Rank:</label>
                        <input type="text" name="rank" placeholder="Ex: Firefighter I" value="<?php echo $rank;?>">
                        <label>Employee Service Number:</label>
                        <input type="text" name="sn" placeholder="Ex: 23956" value="<?php echo $sn;?>">
                    </div>
                    <div class="dl">
                        <label>Place Of Off-duty Eployment:</label>
                        <input type="text" name="offduty" placeholder="Los Santos Police Department" value="<?php echo $offduty;?>">
                        <label>Reason For Off-duty Employment:</label>
                        <input type="text" name="reason" placeholder="Ex: Reason" value="<?php echo $reason;?>">
                    </div>
                    <div class="tl">
                        <label>Additional Information:</label>
                        <input type="text" name="ai" placeholder="Ex: Information" value="<?php echo $ai;?>">
                    </div>
                    <center>  <input id ="submit" type="submit" class="imputonlick" name="submit" value="Submit" onclick="arata('arata2'); return false;">
                        <input  type="submit" class="imputonlick" name="reload" value="Reload" onclick="arata();return true; curata();">
                    </center>
                </form>
            </div>
            <div class="outputcode" id='arata2'>
            <b> <?php
            echo "Title: "; echo $ri;

            echo "<br>";
            echo "<br>";
            echo "<br>";
            echo "<br>";

            echo "[divbox=white][center][img]https://i.imgur.com/ujHmoAV.jpg[/img][/center]";
            echo '<br>';

            echo "[list=none] ";
            echo date("F d"), ", ", date("Y");
            echo "<br>";
            echo "Departmental Request:";
            echo "<br>";

            echo "[b][u]Purpose[/u][/b]";
            echo "<br>";
            echo " [list=none]";
            echo "<br>";
            echo " Upon submission of this official request document — in accordance with the Los Santos Fire Department administrative documentation procedure — (Chief) Fire Officers will thoroughly analyze the request by the employee and determine eligibility.";
            echo "<br>";
            echo "[/list]";
            echo "<br>";

            echo "[b][u]Details[/u][/b]";
            echo "<br>";
            echo "[list=none]";
            echo "[*] [b]EMPLOYEE NAME[/b]: ", $name;
                echo "<br>";
            echo "[*] [b]EMPLOYEE RANK[/b]: ", $rank; 
                echo "<br>";
            echo "[*] [b]EMPLOYEE SERVICE NUMBER[/b]: ", $sn ;
                echo "<br>";
            echo "[size=1].[/size]";
            echo "[*] [b]REQUEST ITEM[/b]: ", $ri    ; 
            echo "<br>";
            echo "[*] [b]PLACE OF OFF-DUTY EPLOYMENT[/b]: ", $offduty ;
                echo "<br>";
            echo "[*] [b]REASON FOR OFF-DUTY EMPLOYMENT:[/b]: ", $reason;
                echo "<br>";
            echo "[/list][list=none]";
            echo "<br>";
            echo "[*] [b]ADDITIONAL INFORMATION[/b]: ", $ai;
                echo "<br>";
            echo "[/list]";
            echo "<br>";
            echo "[/divbox]";

            ?>
            </div>
    </div>
        </div>
    </div>

public function find($user = null) {
		if ($user) {
			$field = (is_numeric($user)) ? 'id' :'username';
			$data = $this->_db->get('users', array($field, '=', $user));
			//var_dump($data);
			//die();

			if ($data->count()) {
				
				$this->_data = $data->first();
				return true;
			}
		}
		return false;
	}