My local docker environment consists of app and web.

services:
  app:
    build:
      context: ./docker/services/app
      dockerfile: app.dockerfile
    working_dir: /var/www
    volumes:
      - ./src:/var/www
    networks:
      - internal

  web:
    build:
      context: ./docker/services/web
      dockerfile: web.dockerfile
    working_dir: /var/www
    volumes:
      - ./src:/var/www
    ports:
      - "8080:80"
    depends_on:
      - app
    networks:
      - internal

networks:
  internal:
    driver: bridge

The app is Laravel based on FROM php:8.3-fpm and the web is Nginx on FROM nginx:1.25 with vhost.conf of:

server {
    listen 80;
    index index.php index.html;
    root /var/www/public;

    location / {
        try_files $uri /index.php?$args;
    }

    location ~ .php$ {
        fastcgi_split_path_info ^(.+.php)(/.+)$;
        fastcgi_pass app:9000;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_param PATH_INFO $fastcgi_path_info;
    }
}

The only route I have is:

<?php

use AppServicesTenantService;
use IlluminateSupportFacadesRoute;

Route::get('/', function (IlluminateHttpRequest $request) {
    /** @var TenantService $service */
    $service = app()->make(TenantService::class);

    dd($service->getTenantName($request));
});

My service class is:

<?php

namespace AppServices;

use IlluminateHttpRequest;

class TenantService
{
    public function getTenantName(Request $request): string
    {
        $chunks = explode('.', $request->getHttpHost());
        $subdomain = $chunks[0] ?? null;

        dd($chunks, 'the subdomain is: ' . $subdomain);
    }
}

Finally, how is it possible that I can provide any (gibberish) subdomain into the URL and both Docker and Laravel will understand it, while I did not (!) add such a subdomain into /etc/hosts?

 cat /etc/hosts
##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1   localhost
255.255.255.255 broadcasthost
::1             localhost

#0.0.0.0        ocsp.apple.com

# Added by Docker Desktop
# To allow the same kube context to work on the host and the container:
127.0.0.1 kubernetes.docker.internal
# End of section

The following dummy URLs work with no issues whatsoever.

It is exactly what I want, but I don’t understand how it works out of box. Especially after reading this.

Normally if I’m not mistaken I would have to add entry like:

127.0.0.1 acme.localhost

to be able to reach acme tenant, but I didn’t have to do this. Why?