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Bots and Indexing on Pantheon

Information on managing bots and indexing while avoiding performance degradation on your Pantheon WordPress or Drupal site.

Bots are part of every public-facing website's lifecycle. We wouldn't be able to find a thing on the internet without them! Bots perform the hard work taken for granted when browsing the multitudes of indexed search results from any given search engine. In the wrong hands, bots can become nagging nuisances slowing down or even taking down your site.

Bots in My Logs: Real World Scenarios and Identifiers

Bots don't browse like humans. Analyzing access patterns in the nginx log is one of the quickest ways to determine the presence of bots.

Rapid Fire Requests/Duplicates

In the log snippet below, there are multiple requests coming in for the same path in rapid fire succession. The time stamp reflects 5 identical requests at the same millisecond. You should investigate these requests. - - [11/Nov/2013:19:05:24 +0000] "POST /index.php?q=comment/reply/545 HTTP/1.0" 500 588 "" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; MRA 4.3 (build 51720))" 0.848 ",, ::ffff:,::ffff:"
unix: - - [11/Nov/2013:19:05:24 +0000] "POST /index.php?q=comment/reply/545 HTTP/1.0" 500 588 "" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; MRA 4.3 (build 51720))" 1.059 ",, ::ffff:,::ffff:" - - [11/Nov/2013:19:05:24 +0000] "POST /index.php?q=comment/reply/545 HTTP/1.0" 500 588 "" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; MRA 4.3 (build 51720))" 1.059 ",, ::ffff:,::ffff:"
unix: - - [11/Nov/2013:19:05:24 +0000] "POST /index.php?q=comment/reply/545 HTTP/1.0" 500 588 "" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; MRA 4.3 (build 51720))" 1.271 ",, ::ffff:,::ffff:" - - [11/Nov/2013:19:05:24 +0000] "POST /index.php?q=comment/reply/545 HTTP/1.0" 500 588 "" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; MRA 4.3 (build 51720))" 1.271 ",, ::ffff:,::ffff:"
unix:\xC8\xFB\x7F - - [11/Nov/2013:19:05:24 +0000] "POST /index.php?q=comment/reply/545 HTTP/1.0" 500 588 "" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; MRA 4.3 (build 51720))" 1.481 ",, ::ffff:,::ffff:" - - [11/Nov/2013:19:05:24 +0000] "POST /index.php?q=comment/reply/545 HTTP/1.0" 500 588 "" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; MRA 4.3 (build 51720))" 1.482 ",, ::ffff:,::ffff:"

Bots Converging on Erroring Pages

Some legitimate bots/crawlers/proxies (such as BingBot or AdsBotGoogle) will identify themselves. Since search-indexing is desirable for most sites, tread carefully in order to avoid wreaking havoc on a site's SEO. That said, there may be instances in which crawlers/spiders converge on a page that is erroring out ( 502s in the example below). These repetitive requests can increase the pageload issues by putting more load on the server. Investigate these errors immediately. When the error has been fixed, the bots/crawlers will no longer be hung-up on the give path. - - [26/Jul/2013:15:27:38 +0000] "GET /index.php?q=shop/kits/shebang-kit HTTP/1.0" 502 166 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +" 14.188 ",,,"
unix: - - [26/Jul/2013:15:27:38 +0000] "GET /index.php?q=shop/kits/shebang-kit HTTP/1.0" 502 166 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +" 14.476 ",,," - - [26/Jul/2013:15:27:38 +0000] "GET /index.php?q=shop/kits/shebang-kit HTTP/1.0" 502 166 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +" 14.477 ",,," - - [26/Jul/2013:15:26:37 +0000] "GET /index.php?q=gush/content/name-pimp-november-2008&page=17 HTTP/1.0" 502 166 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +" 14.722 ",,," - - [26/Jul/2013:15:26:37 +0000] "GET /gush/content/name-pimp-november-2008?page=17 HTTP/1.1" 502 166 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +" 14.999 ",,,"
unix: - - [26/Jul/2013:15:26:37 +0000] "GET /index.php?q=gush/content/name-pimp-november-2008&page=17 HTTP/1.0" 502 166 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +" 14.998 ",,," - - [26/Jul/2013:15:31:03 +0000] "GET / HTTP/1.1" 500 109 "-" "" 0.126 ",,,"

Indexing Your Pantheon Site

While Drupal and WordPress both generate their own robots.txt file by default, a custom or CMS-standard robots.txt will only work in Live environments of a paid site with a custom domain. It is important to note that each of your site environments have a robots.txt file associated with the platform domain (e.g., or custom Vanity domain (e.g., that contains the following:

# Pantheon's documentation on robots.txt:
User-agent: *
Disallow: /

User-agent: RavenCrawler
User-agent: rogerbot
User-agent: dotbot
User-agent: SemrushBot
User-agent: SiteAuditBot
User-agent: SplitSignalBot
User-agent: PowerMapper
User-agent: Swiftbot
User-agent: lyticsbot
User-agent: Dubbotbot
User-agent: PopeTech-CrawlBot
User-agent: PopeTech-ScanBot
Allow: /

Additionally, Pantheon's edge layer adds the X-Robots-Tag: noindex HTTP header when serving requests from platform domains (e.g. This instructs most bots/crawlers not to index the page and prevents it from being returned in search results.

Indexing Before You Launch

The domains are intended for development use and cannot be used for production. Adding sub-domains (i.e., for DEV or TEST will remove the X-Robots-Tag: noindex header only, but still serve the Pantheon robots.txt from the platform domain.

To support pre-launch SEO and site search testing, we allow the following bots access to platform domains:

Some tools (like Siteimprove or ScreamingFrog) can be set to ignore robots.txt when scanning. If you're testing links or SEO with other tools, you may request the addition of the tool to our robots.txt file by contacting support to create a feature request. Otherwise, you can connect a custom domain (like to the Live environment and test your links following the alternative domain.

If you run SEO toolsets locally, you can utilize an /etc/hosts file entry on your local development box to spoof your production domain on Pantheon:

Note that modifying the hosts file usually requires administrative privileges from the OS.

The location of the hosts file varies depending on your operating system:

  • MacOS / Linux: /etc/hosts
  • Windows: C:\\Windows\System32\Drivers\etc\hosts

Add lines to your operating system's hosts file in the following format:


In the example above, replace the IP addresses with those provided by Pantheon, and the domains with your own.

You can index your site under your production domain once it's added to the Live environment. There are many contrib module options available for creating sitemaps for Drupal, including XMLSiteMap and Site_Map. WordPress users can install the Google XML Sitemaps or Yoast SEO plugins, which will maintain sitemap updates automatically. It is up to you to configure the extensions to work as you desire. Pantheon does not offer support for Drupal modules or WordPress plugins.

Robots.txt with Composer and Drupal

When using Drupal scaffolding, the root web/robots.txt file will be overwritten on each composer install, whether it is managed locally or on Pantheon using Integrated Composer. For more information, refer to Using Drupal's Composer Scaffold.

Modifications are made in a separate file that is appended to the existing robots.txt. The path and name of the file are arbitrary. In the example below, we'll create a new file in an assets folder located at the root of the website host to which it applies.

In the terminal, run the following command in the root directory of your local Git repository:

touch assets/my-robots-additions.txt

You can now add your changes into that newly created file using a text editor.

Modify the site's root composer.json file to append this new file when copying Drupal's scaffolding. The ... represents existing content. If you already have "file-mapping", content can be added to the section.

"file-mapping": {
    "[web-root]/robots.txt": {
        "append": "assets/my-robots-additions.txt"

You can test this locally using composer install. If successful, use the following commands to commit changes:

git add assets/my-robots-additions.txt composer.json
git commit -m "Append robots.txt changes via composer"

Robots.txt for Front-End Sites

You can use a robots.txt file on Next.js and Gatsby Front-End Sites frameworks. Refer to Drupal + Next.js, WordPress + Next.js, or WordPress + Gatsby for more information.


Robots.txt conflicting with Composer

The default Drupal upstream includes a line in .gitignore to exclude tracking web/robots.txt because it is automatically generated during composer install. Occasionally, this is removed and modifications to robots.txt are committed. This will cause a merge conflict when attempting to run composer, and will cause builds to fail on Integrated Composer.

Move the accidentally tracked file out of the repository and into .gitignore. You may want to pull any changes you need out of this file and in to a temporary text file for later use.

In the terminal, run the following commands in the root directory of your local Git repository:

git rm --cached web/robots.txt
git commit -m "Remove auto-generated robots.txt"

In your text editor add the following to .gitignore:


Commit that change using the following command:

git add .gitignore
git commit -m "Do not track changes to generated robots.txt"

You can now proceed with the recommended method of using Robots.txt with Composer and Drupal

Sitemaps Produce a White Screen of Death (WSOD)

Some modules or plugins are configured by default to fetch all URLs at once during sitemap generation which can result in a blank white page (WSOD) due to exceeding PHP's memory limit. To resolve this issue, adjust the plugin or module configuration so that URLs are fetched individually instead of all at once.

For example, if you have a Drupal site using the XMLSiteMap module, navigate to admin/config/search/xmlsitemap/settings and uncheck Prefetch URL aliases during sitemap generation. Save the configuration and clear caches for the Live environment on the Pantheon Dashboard or via Terminus:

terminus env:clear-cache

Props to Will Hall for highlighting this solution in a related blog post.

Legacy Sitemap Submissions Generating 404s

Sitemaps can (and should) be submitted directly to Google Webmaster Tools. However, if there are legacy submissions out there generating 404s, you'll need to redirect via PHP within wp-config.php or settings.php. For example, WordPress sites running the Yoast SEO plugin can use the following:

// 301 Redirect from /sitemap.xml to /sitemap_index.xml
if (($_SERVER['REQUEST_URI'] == '/sitemap.xml') &&
  (php_sapi_name() != "cli")) {
  header('HTTP/1.0 301 Moved Permanently');
  header('Location: /sitemap_index.xml');

For more examples of redirecting via PHP, see Configure Redirects.

Incorrect robots.txt Output in WordPress

In WordPress, do not enable Discourage search engines from indexing this site on Dev or Test environments. This option is set in Settings > Reading > Search Engine Visibility in the WordPress Admin Dashboard.

This setting creates a built-in robots.txt file that disallows or blocks crawlers. While the file applied by the platform normally overrides it, it doesn't when there's a trailing slash on the URL pointing to robots.txt.

As a workaround, you can override the output by creating your custom filter for robots_txt. You can add this as a custom plugin, or an entry in your theme's functions.php file:

add_filter('robots_txt', 'custom_robots_txt', 10,  2);

function custom_robots_txt($output, $public) {

    $robots_txt =  "User-agent: * \n";
    $robots_txt .=  "Sitemap: \n";
    $robots_txt .=  "Disallow: /secure/ ";
    // add more $robots_txt .= for each line

    return $robots_txt;