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Primary Domains

Learn more about choosing your primary domain.

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This section provides information on how to choose and configure your primary domain.

Choose Primary Domain

Pantheon uses the term primary domain to refer to a single domain used to serve all traffic from a site. For example, configuring www.example.com as the primary domain means that requests to example.com (or any other custom domain connected to the environment) all get redirected to www.example.com. This assumes that you have added both example.com and www.example.com to the Site Dashboard.

Redirecting all traffic to a primary domain is a best practice for SEO since it avoids duplicate content. It also prevents session strangeness, where a user can be logged in to one domain but logged out of other domains at the same time, and it can make it easier to measure and monitor website traffic.

Choose a primary domain from the dropdown at the bottom of Domains / HTTPS:

Set the primary domain in the Site Dashboard

Note

Redirects cannot be managed via .htaccess, which is ignored on our platform. For details, refer to Configure Redirects.

Set a Primary Domain via the Dashboard

Warning

With a Primary Domain set at the platform level, all other domains (except the platform domain) will be pointed to your Primary domain at the root level. If you want to redirect secondary domains to specific pages on your site (for example, olddomain.com to newdomain.com/old-landing-page), do not set a Primary Domain. Instead use PHP redirects.

  1. Navigate to the environment you want to set a primary domain for (typically Test or Live), and then select Domains / HTTPS.

  2. Ensure that all domains have been added and are listed.

  3. Navigate to the Choose Primary Domain section, select the domain to which traffic should be redirected, and then click Save Configuration.

Note

You will only see the primary redirect option when you have two or more custom domains attached to your environment. If you want to redirect a single platform domain, you must do the primary redirect via PHP. For example, live-mysite.pantheonsite.io to www.example.com

Set a Primary Domain with Terminus

  1. Install or upgrade to the latest version of Terminus.

  2. Use Terminus to add the primary domain. In this example, replace:

    • my-site with your site name
    • live if you'd like to set it for a different environment
    • www.example.com with your primary domain
    terminus domain:primary:add my-site.live www.example.com

Update or Remove Primary Domain

Update the Primary Domain using either method provided in the previous section.

Remove an existing selection for the Primary Domain on any environment using Terminus:

terminus domain:primary:remove my-site.live

Replace my-site with your site name, and live with the environment you're removing a primary domain from.

Verify

You can confirm that the Primary Domain has been removed with cURL pointed at one of your other custom domains, which would previously have been redirected:

curl -I https://example.com
HTTP/2 301
retry-after: 0
server: Pantheon
location: https://www.example.com/
x-pantheon-redirect: primary-domain-policy-docdate: Wed, 05 Feb 2020 16:43:21 GMT
x-served-by: cache-mdw17355-MDW
x-cache: HIT
x-cache-hits: 0
x-timer: S1580921002.586800,VS0,VE1
age: 0
accept-ranges: bytes
via: 1.1 varnish
content-length: 0

The presence of x-pantheon-redirect: primary-domain-policy-doc indicates that the domain is still being pointed at the former Primary Domain. Contact support if this value persists.

Redirect to HTTPS

It's a best practice for SEO and security to standardize all traffic on HTTPS and choose a primary domain. Configure redirects to the primary domain with HTTPS in pantheon.yml

Redirect with PHP

If your site configuration prevents you from setting the primary domain from the platform level, you can use PHP redirects:

PHP Redirection

Add the following to wp-config.php, usually placed above /* That's all, stop editing! Happy Pressing. */. Don't forget to replace www.example.com:

wp-config.php
if (isset($_ENV['PANTHEON_ENVIRONMENT']) && php_sapi_name() != 'cli') {
  // Redirect to https://$primary_domain in the Live environment
  if ($_ENV['PANTHEON_ENVIRONMENT'] === 'live') {
    // Replace www.example.com with your registered domain name.
    $primary_domain = 'www.example.com';
  }
  else {
    // Redirect to HTTPS on every Pantheon environment.
    $primary_domain = $_SERVER['HTTP_HOST'];
  }

  $requires_redirect = false;
  
  // Ensure the site is being served from the primary domain.
  if ($_SERVER['HTTP_HOST'] != $primary_domain) {
    $requires_redirect = true;
  }

  // If you're not using HSTS in the pantheon.yml file, uncomment this next block.
  // if (!isset($_SERVER['HTTP_USER_AGENT_HTTPS'])
  //     || $_SERVER['HTTP_USER_AGENT_HTTPS'] != 'ON') {
  //   $requires_redirect = true;
  // }

  if ($requires_redirect === true) {

    // Name transaction "redirect" in New Relic for improved reporting (optional).
    if (extension_loaded('newrelic')) {
      newrelic_name_transaction("redirect");
    }

    header('HTTP/1.0 301 Moved Permanently');
    header('Location: https://'. $primary_domain . $_SERVER['REQUEST_URI']);
    exit();
  }
}

WordPress users should also run a search and replace to update any references to the platform domain.

More Resources