Troubleshooting $_SERVER['HTTP_HOST'] Resolving To Target Domain In Plesk With Nginx Proxy

Hey guys! Ever run into that head-scratcher where your $_SERVER['HTTP_HOST'] variable in Plesk with an Nginx proxy setup stubbornly returns the target domain instead of the actual domain alias? Yeah, it's a common issue, especially when you're juggling a PrestaShop Multistore or similar configurations. Let's dive deep into why this happens and, more importantly, how to fix it. We'll break it down step by step, so you can get your domains playing nice in no time.

Understanding the Issue: Why the Wrong Host?

So, what's the deal with $_SERVER['HTTP_HOST] showing the wrong domain? To really grasp this, you need to understand how Plesk, Nginx, and domain aliases work together. The $_SERVER['HTTP_HOST'] variable is a PHP superglobal that contains the hostname sent in the HTTP Host header by the client's browser. This header is crucial because it tells the web server which website the user is trying to access when multiple domains or aliases point to the same server.

Nginx as a Reverse Proxy

In a Plesk environment with Nginx as a reverse proxy, Nginx sits in front of Apache (or PHP-FPM) and handles incoming HTTP requests. When a request comes in, Nginx determines which backend server to forward the request to based on the Host header. This setup is fantastic for performance because Nginx is incredibly efficient at serving static content and handling SSL termination, freeing up Apache to focus on dynamic content. However, this proxy setup can also be the root of our $_SERVER['HTTP_HOST'] problem.

When Nginx proxies the request, it might not always pass the original Host header to the backend. Instead, it might use the target domain, which is the primary domain associated with the Plesk subscription. This is where things get tricky. Your PHP application, relying on $_SERVER['HTTP_HOST'] to determine the correct website, ends up seeing the target domain instead of the domain alias the user actually used. For instance, if a user accesses alias.example.com, your application might incorrectly see example.com.

Domain Aliases in Plesk

Domain aliases in Plesk are like extra doorways to your website. They allow you to have multiple domain names point to the same website content. This is super useful for branding, marketing campaigns, or even just preventing typos from leading visitors to an error page. However, when $_SERVER['HTTP_HOST'] gets confused, your application can't differentiate between the alias and the primary domain, leading to all sorts of issues, especially in a multistore environment where each store needs to be identified by its unique domain.

Multistore Complications

If you're running a multistore setup like PrestaShop, this issue is amplified. Each store in your multistore relies on the correct $_SERVER['HTTP_HOST'] value to load the appropriate store configuration, theme, and content. When the wrong domain is detected, users might be redirected to the wrong store, see incorrect pricing, or even encounter errors. It's like walking into the wrong room in a house – not a great experience!

In summary, the core issue stems from Nginx's proxy configuration potentially overwriting the original Host header with the target domain. This messes with PHP's ability to correctly identify the accessed domain alias, causing problems for applications that rely on this information.

Diagnosing the Issue: Is It Really $_SERVER['HTTP_HOST']?

Before we jump into fixes, let’s make sure $_SERVER['HTTP_HOST'] is indeed the culprit. There are a few simple ways to confirm this. Firstly, you can add a small snippet of PHP code to your website to output the contents of the $_SERVER array. Create a file, say test.php, in your website's root directory with the following code:

<?php
phpinfo();
?>

Then, access this file via your domain alias (e.g., alias.example.com/test.php) and your target domain (e.g., example.com/test.php). Look for the $_SERVER['HTTP_HOST'] value in the output. If you see the target domain for both, you've confirmed the issue.

Alternatively, you can use a simpler script to just print the value of $_SERVER['HTTP_HOST']:

<?php
echo 'HTTP_HOST: ' . $_SERVER['HTTP_HOST'];
?>

This will give you a cleaner output and quickly show you the value being passed.

Another way to diagnose the issue is by examining your application's logs. If you're using PrestaShop, for example, check the logs for any errors related to domain mismatch or incorrect store loading. These logs often contain valuable clues about what's going wrong behind the scenes. By carefully analyzing these logs, you can pinpoint whether $_SERVER['HTTP_HOST'] is indeed the root cause or if there might be other factors at play.

It’s also worth checking your application's configuration files. Some applications have their own domain settings that might be overriding the value from $_SERVER['HTTP_HOST']. Make sure these settings are correctly configured to use the domain aliases as intended.

Once you've confirmed that $_SERVER['HTTP_HOST'] is the problem, you can confidently move on to implementing the solutions. But remember, a solid diagnosis is half the battle won!

Solutions: Fixing the Host Header Issue

Alright, so you've confirmed that $_SERVER['HTTP_HOST'] is playing tricks on you. No sweat! There are several ways to tackle this, and we'll walk through the most effective ones. The key is to ensure Nginx correctly passes the original Host header to the backend.

1. Custom Nginx Configuration

The most common and robust solution involves customizing your Nginx configuration. You need to tell Nginx to explicitly pass the Host header when proxying the request. This is done by adding the proxy_set_header directive to your Nginx configuration file. Here's how:

Accessing the Nginx Configuration

In Plesk, you don't directly edit the main Nginx configuration files. Instead, you use the