Multi-Region Architecture for a Bitrix E-commerce Store: 27 Cities on Subdomains

server {
    server_name example.com www.example.com ekb.example.com spb.example.com krasnodar.example.com; # and 24 more cities

    location ~ ^/(blog|company/news)/ {
        return 301 https://example.com$request_uri;
    }

    location / {
        proxy_pass http://127.0.0.1:8080;
        proxy_set_header Host $host;
    }
}

<?php
/**
 * Event handlers for subdomain routing and SEO optimization
 * on multi-region 1C-Bitrix projects (Aspro: Max template)
 */
class RegionalSeoHandlers
{
    /**
     * Returns the visitor to their regional subdomain when they leave shared sections.
     * Protects the user context from being lost (falling out of the region).
     */
    public static function returnToRegionalDomain()
    {
        // 1. Skip admin panel, REST API, AJAX and CLI so we don't break system processes
        if (defined('ADMIN_SECTION') && ADMIN_SECTION === true) return;
        if (php_sapi_name() === 'cli') return;
        if (isset($_SERVER['HTTP_BX_AJAX']) || isset($_REQUEST['ajax']) || (isset($_SERVER['HTTP_X_REQUESTED_WITH']) && $_SERVER['HTTP_X_REQUESTED_WITH'] == 'XMLHttpRequest')) return;
        if (strpos($_SERVER['REQUEST_URI'], '/bitrix/') === 0 || strpos($_SERVER['REQUEST_URI'], '/rest/') === 0) return;

        $host = str_replace('www.', '', $_SERVER['HTTP_HOST']);
        $uri = $_SERVER['REQUEST_URI'];

        // TODO: set your main domain (no protocol)
        $mainDomain = 'example.com';

        // 2. Excluded sections that physically exist only on the main domain
        // TODO: list your shared section directories separated by |
        $isExcluded = preg_match('#^/(blog|company/news)/#i', $uri);

        // 3. Visitor is on the main domain but entered a regular section (catalog, cart, etc.)
        if ($host === $mainDomain && !$isExcluded) {

            // Read the region ID straight from the user's cookie (set by the Aspro component)
            $regionCookieId = isset($_COOKIE['current_region']) ? (int)$_COOKIE['current_region'] : 0;

            if ($regionCookieId > 0 && \Bitrix\Main\Loader::includeModule('iblock')) {

                // Fetch the region's domain directly from the iblock database
                $dbRegion = \CIBlockElement::GetList(
                    [],
                    ['ID' => $regionCookieId, 'ACTIVE' => 'Y'],
                    false,
                    false,
                    ['ID', 'IBLOCK_ID', 'PROPERTY_MAIN_DOMAIN']
                );

                if ($arRegion = $dbRegion->Fetch()) {
                    $regionDomain = $arRegion['PROPERTY_MAIN_DOMAIN_VALUE'];
                    $regionDomain = trim(str_replace(['http://', 'https://'], '', $regionDomain));

                    // 4. Instant redirect if the domain exists and differs from the main one
                    if (!empty($regionDomain) && $regionDomain !== $mainDomain) {
                        // Keep GET parameters (filters, pagination, utm tags)
                        $queryString = $_SERVER['QUERY_STRING'] ? '?' . $_SERVER['QUERY_STRING'] : '';
                        $newUrl = 'https://' . $regionDomain . current(explode('?', $uri)) . $queryString;

                        LocalRedirect($newUrl, true, '301 Moved Permanently');
                    }
                }
            }
        }
    }

    /**
     * SEO patch: forcibly replaces relative and wrongly generated
     * regional links with absolute main-domain URLs.
     */
    public static function forceAbsoluteLinksForMainSections(&$content)
    {
        // Skip system and AJAX requests
        if (
            (defined('ADMIN_SECTION') && ADMIN_SECTION === true) ||
            php_sapi_name() === 'cli' ||
            strpos($_SERVER['REQUEST_URI'], '/bitrix/') === 0 ||
            strpos($_SERVER['REQUEST_URI'], '/rest/') === 0 ||
            (isset($_SERVER['HTTP_X_REQUESTED_WITH']) && $_SERVER['HTTP_X_REQUESTED_WITH'] == 'XMLHttpRequest') ||
            (isset($_REQUEST['ajax']) && strtolower((string)$_REQUEST['ajax']) === 'y')
        ) {
            return;
        }

        // TODO: set your main domain (with protocol)
        $mainDomain = 'https://example.com';

        // Rule 1: relative links (e.g. href="/blog/...")
        // TODO: list your shared sections
        $content = preg_replace(
            '/(href=["\'])\/(blog|company\/news)\//i',
            '$1' . $mainDomain . '/$2/',
            $content
        );

        // Rule 2: links where the component already inserted a subdomain (href="https://ekb.example.com/blog/...")
        // TODO: escape the dots in your domain name (e.g. example\.com)
        $content = preg_replace(
            '/(href=["\'])https?:\/\/[a-zA-Z0-9-]+\.example\.com\/(blog|company\/news)\//i',
            '$1' . $mainDomain . '/$2/',
            $content
        );
    }
}

<?php
// /local/php_interface/init.php

if (strpos($_SERVER['HTTP_HOST'] ?? '', 'crm.example.com') === false) {
    if (file_exists(__DIR__ . '/include/regional_handlers.php')) {
        require_once(__DIR__ . '/include/regional_handlers.php');

        // Return the visitor to their region when leaving global sections
        AddEventHandler(
            "main",
            "OnPageStart",
            ["RegionalSeoHandlers", "returnToRegionalDomain"]
        );

        // Strip regional links to global sections from the HTML
        AddEventHandler(
            "main",
            "OnEndBufferContent",
            ["RegionalSeoHandlers", "forceAbsoluteLinksForMainSections"]
        );
    }
}