Set Up and Manage a WordPress Multisite Network

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August 1, 2023 WordPress
Set Up and Manage a WordPress Multisite Network

WordPress Multisite is a feature built into WordPress core that allows a single installation to host a network of independent sites — each with its own content, users, settings, and plugins — while sharing a single codebase, database, and file upload directory. Activating Multisite converts wp-config.php and .htaccess to network-aware configurations and switches the database from single-site tables to a table-per-site scheme: the main site keeps the original tables (wp_posts, wp_options, etc.) while each additional site gets its own prefixed set (wp_2_posts, wp_2_options, etc.), and shared tables (wp_users, wp_usermeta, wp_blogs, wp_site) span the entire network. Networks can be configured in two URL modes: subdomain mode (site2.example.com) or subdirectory mode (example.com/site2/) — subdomain mode requires wildcard DNS and a wildcard SSL certificate, while subdirectory mode works with a standard single-domain certificate. The Super Admin role is the highest privilege level in a network — Super Admins manage plugins and themes at the network level, whereas individual site administrators manage content and site-level settings. Plugins activated at the network level via Network Admin → Plugins are forced-active on all sites and cannot be deactivated by individual site admins — this is the correct approach for security plugins, caching plugins, and shared functionality. Per-site plugin activation is available when a plugin is not network-activated, giving site admins the choice to enable or disable it. The switch_to_blog() function (and its companion restore_current_blog()) allows PHP code to query or modify another site in the network — used in network-wide reports, search aggregators, and cron jobs that process all sites. User roles are site-scoped: a user can be an Administrator on site 2 and a Subscriber on site 3, with capabilities stored in per-site wp_N_usermeta rows. The CSP headers post covers how to apply security headers network-wide from a single mu-plugin rather than per site.

Problem: A marketing agency manages 12 client microsites that share the same WordPress theme and a set of internal plugins — each site is a separate WordPress installation, so plugin updates must be applied 12 times and user accounts must be created separately on each site, multiplying maintenance overhead.

Solution: Convert the primary installation to a WordPress Multisite network, migrate client sites as child sites, network-activate shared plugins, and use a single network admin panel for updates and user management across all 12 sites.

// ── Step 1: Enable Multisite in wp-config.php ─────────────────────────────
// Add BEFORE "That's all, stop editing!" line:
define( 'WP_ALLOW_MULTISITE', true );

// After running Network Setup in WP Admin → Tools → Network Setup,
// wp-config.php gets these additional constants:
define( 'MULTISITE',          true );
define( 'SUBDOMAIN_INSTALL',  false );    // true for subdomain mode
define( 'DOMAIN_CURRENT_SITE','example.com' );
define( 'PATH_CURRENT_SITE',  '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

// ── Step 2: Programmatically create a new site in the network ─────────────
function agency_create_client_site( array $args ): int|WP_Error {
    $defaults = [
        'domain'     => '',     // subdirectory slug or subdomain
        'title'      => '',
        'user_email' => '',
        'user_role'  => 'administrator',
        'options'    => [],
    ];
    $args = wp_parse_args( $args, $defaults );

    // Build the full domain / path depending on network mode
    if ( is_subdomain_install() ) {
        $domain = sanitize_title( $args['domain'] ) . '.' . DOMAIN_CURRENT_SITE;
        $path   = '/';
    } else {
        $domain = DOMAIN_CURRENT_SITE;
        $path   = '/' . sanitize_title( $args['domain'] ) . '/';
    }

    $site_id = wpmu_create_blog(
        $domain,
        $path,
        sanitize_text_field( $args['title'] ),
        get_current_user_id(),
        [ 'public' => 1 ],
        get_current_network_id()
    );

    if ( is_wp_error( $site_id ) ) {
        return $site_id;
    }

    // Add an external admin user to the new site
    if ( $args['user_email'] ) {
        $user = get_user_by( 'email', sanitize_email( $args['user_email'] ) );
        if ( $user ) {
            add_user_to_blog( $site_id, $user->ID, $args['user_role'] );
        }
    }

    // Apply site-specific options after creation
    switch_to_blog( $site_id );
    foreach ( $args['options'] as $key => $value ) {
        update_option( sanitize_key( $key ), $value );
    }
    restore_current_blog();

    return $site_id;
}

// Usage
$new_site = agency_create_client_site([
    'domain'     => 'client-alpha',
    'title'      => 'Client Alpha Microsite',
    'user_email' => 'admin@client-alpha.com',
    'options'    => [
        'blogdescription' => 'Official site of Client Alpha',
        'timezone_string' => 'America/New_York',
    ],
]);

// ── Step 3: Network-wide query across all sites ───────────────────────────
function agency_get_all_sites_post_count(): array {
    $counts = [];
    foreach ( get_sites( [ 'number' => 500 ] ) as $site ) {
        switch_to_blog( $site->blog_id );
        $counts[ $site->blog_id ] = [
            'name'  => get_bloginfo( 'name' ),
            'posts' => wp_count_posts()->publish,
        ];
        restore_current_blog();
    }
    return $counts;
}

NOTE: Converting an existing single-site WordPress installation to Multisite is a one-way operation — there is no built-in revert path. Take a full database and file backup before enabling Multisite. Also note that not all plugins are Multisite-compatible: plugins that assume a single site’s table prefix or hardcode the site URL will break on secondary sites. Test every plugin on a staging network before network-activating it in production.

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