How to make a maintenance mode for your Symfony website

Developing a website is synonymous of multiple releases which can cause some undesirables critical errors.

In this tutorial, we will learn how to make a simple and efficient maintenance mode with Symfony.

Furthermore, you'll still be able to access your website while maintenance mode is active.

Let's go.

First of all, we need to define a new parameter with a boolean value you will use to toggle maintenance on or off.

Do the following in your parameters.yml file :

#app/config/parameters.yml

parameters:
    maintenance: false

Keep it to false for now.

Then, we will create the listener class that will detect if maintenance is enabled. We will name it MaintenanceListener.php

<?php

namespace AcmeBundle\EventListener;

use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\HttpFoundation\Response;


class MaintenanceListener
{
    private $container;

    public function __contruct(ContainerInterface $container)
    {
        $this->container = $container;
    }

    public function onKernelRequest(GetResponseEvent $event)
    {
        // This will get the value of our maintenance parameter
        $maintenance = $this->container->hasParameter('maintenance') ? $this->container->getParameter('maintenance') : false;

        // This will detect if we are in dev environment (app_dev.php)
        $debug = in_array($this->container->get('kernel')->getEnvironment(), ['dev']);

        // If maintenance is active and in prod environment
        if ($maintenance && !$debug) {
            // We load our maintenance template
            $engine = $this->container->get('templating');
            $template = $engine->render('::maintenance.html.twig');

            // We send our response with a 503 response code (service unavailable)
            $event->setResponse(new Response($template, 503));
            $event->stopPropagation();
        }
    }
}

And now the service declaration :

#AcmeBundle/Resources/config/services.xml

<service id="acme.maintenance_mode" class="AcmeBundle\EventListener\MaintenanceListener">
    <argument type="service" id="service_container" />
    <tag name="kernel.event_listener" event="kernel.request" method="onKernelRequest" />
</service>

So we have now a MaintenanceListener class which will disable your website in a production environment if you set it to true. Cool isn't it ?

Don't forget to create your own maintenance template in app/Resources/views/maintenance.html.twig

<!DOCTYPE html>
<head>
    <meta charset="utf-8">
    <title>Site temporarily under maintenance</title>
</head>
<body>
    <h1>Site temporarily under maintenance</h1>
    <p>Sorry for the inconvenience, we will get back soon !</p>
</body>
</html>

That's all folks, I hope this tutorial helped you ! :)

Do not hesitate to give me your feedback or asking some questions !

Hugo.