Ne créer qu'une image docker pour PHP-FPM & Nginx

I have always been bothered by a simple issue when building docker image artifacts for my PHP/Nginx applications. The issue of building two docker image artifacts instead of just one with my PHP source code.

This article is about building only one artifact by just using an Nginx directive instead of another.

A bit of context

My favorite stack for PHP applications is PHP-FPM and Nginx and I have enough ops skills to provision a Kubernetes or Docker swarm cluster for my personal and work-related projects. This means I always have a CI/CD ready to build and deploy my docker image artifacts.

When pushing my code into the PHP-FPM docker image only and deploying my application, I would get errors filled with anger from my containers:

PHP-FPM | GET /index.php” 404
Nginx | realpath() “/var/www/html/public” failed (2: No such file or directory)
Nginx | FastCGI sent in stderr: “Primary script unknown” while reading response header from upstream

My guess was that not having my source code in the Nginx docker image prevented Nginx from passing the request to PHP-FPM. Sure enough, adding the source code in the Nginx docker image fixed the issue every single time.

But then, I had to build 2 images with the exact same source code: one for PHP-FPM and one for Nginx, just so Nginx could do its request pass-through job.

To be honest, it bugged me for quite some time, but I never got to wrap my head around the issue.

Until this day.

The bottom line

Symfony, which I use almost every time I deal with MVC applications, has a nice Nginx snippet to get your application up & running.

server {
    # [...]
    location ~ ^/index\.php(/|$) {
        fastcgi_pass php-fpm-endpoint:9000;
        fastcgi_split_path_info ^(.+\.php)(/.*)$;
        include fastcgi_params;

        fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
        fastcgi_param DOCUMENT_ROOT $realpath_root;
        internal;
    }
}

I am no wizard, and my Nginx skills mainly consist of ⌘ + C and ⌘ + V with some editing along the way. This means I had to try & fail for about 2 hours with Stack Overflow as my only friend to find a better solution.

However, after all these failures and Stack Overflow not really helping me out, I stumbled upon some Nginx documentation and made a bald move: using $document_root instead of $realpath_root.

server {
    # [...]
    location ~ ^/index\.php(/|$) {
        fastcgi_pass php-fpm-endpoint:9000;
        fastcgi_split_path_info ^(.+\.php)(/.*)$;
        include fastcgi_params;

        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;        fastcgi_param DOCUMENT_ROOT $realpath_root;
        internal;
    }
}

From the said Nginx documentation:

$document_root: root or alias directive’s value for the current request

$realpath_root: an absolute pathname corresponding to the root or alias directive’s value for the current request, with all symbolic links resolved to real paths

There is an important word for $realpath_root, in case you did not catch it: resolved. We are in the Nginx context: for Nginx to resolve a path, it needs to access the file system context which it could not without the source code.

$document_root fixes this as it uses the root directive directly.

Takeaway

When dealing with PHP-FPM artifacts and Nginx in a docker context, use $document_root for your fastcgi_param SCRIPT_FILENAME directive instead of $realpath_root in your Nginx configuration.

It will allow you to build one and only one PHP-FPM docker image artifact and to use the raw Nginx docker image with just one configuration file to mount.