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5xx Level Errors

Get explanations for 500-level error messages.

This section provides information on how to interpret 5xx errors.

502 Upstream Header Too Big

Upstream sent too big header while reading response header from upstream.

This error occurs when the payload or size of the request sent is greater than the fastcgi_buffer_size. Check to see if you are making heavy requests with a number of assets or data being passed if this happens again.

Remove additional images to reduce the size of the payload sent to the buffer for nginx to process. This will allow you to post the request.

502 Timeout/Segfault Error

This error can happen with HTTP Basic Auth and Drupal’s AJAX when an AJAX request doesn't send the authentication.

Complete the steps below to resolve this:

  1. Disable Basic Auth and send the request again to see if it works.

  2. Re-enable Basic Auth.

However, if it is possible to ensure your headers are always passed for JS files, that is the best solution.

Pantheon 502 Bad Gateway

There was an error connecting to the PHP backend.

Nginx (the web server) reports this problem if the php-fpm process hangs or cannot start.

Pantheon 502 Routing Failure

Page Could Not Be Loaded. The request could not be completed due to a networking failure. Contact support if this issue persists.

This means an internal networking issue has occurred with Styx, Pantheon's routing mesh.

503 First Byte Timeout

Page Could Not Be Loaded. We're very sorry, but the page could not be loaded properly. This should be fixed very soon, and we apologize for any inconvenience.

This error message will be accompanied by a 503 First Byte Timeout page title. This means that the request has exceeded the platform web request timeout of 60 seconds (refer to our timeouts documentation for more information). You can also refer to our documentation on debugging for some helpful insights on how to handle these cases.

503 Header Overflow

Header overflow.

The new Pantheon Global Edge size limit for cookies, sent in the request "Cookie: .." header, is 10KB. If more than 10KB are sent, all cookies are dropped and the request is processed as if no cookies were sent. The header "X-Cookies-Dropped: 1" is added to truncated requests and responses. You can ignore this scenario in your PHP code or handle it by displaying a custom error page.

This response can also occur on Drupal 8 sites using the cacheability debug service, which can generate HTTP headers (for example, X-Drupal-Cache-Tags and X-Drupal-Cache-Contexts) that exceed size limits. Refer to Environment-Specific Configurations for Drupal for more information.

You can reduce the number of set-cookie headers in the response to resolve this error if you receive a 503 error and your cookie size is smaller than 10KB.

Pantheon 503 Database not Responding

The web page you were looking for could not be delivered.

This error indicates that the MySQL database is not responding. It's possible that the MySQL database was suspended and failed to resume.

Error 503 Service Unavailable

This error generally occurs when a request times out. This can indicate a performance issue with the site if your pages take longer to load than the threshold. Learn more about Timeouts on Pantheon.

This can be a misleading message if you're using AJAX when HTTP Basic Auth is enabled (the security username/password). The best workaround is to disable the security option for the environment for testing.

Pantheon 504 Target Not Responding

The web page you were looking for could not be delivered.

A common cause for this error is an idle container that has spun down due to inactivity. Wake the environment by loading the home page in your browser or using the terminus env:wake command.

No php workers are available to handle the request.

This occurs when PHP processing resources for your site are exhausted. Each application container has a fixed limit of requests it can concurrently process. When this limit is reached, nginx will queue up to 100 requests in the hope that PHP workers will free up to serve these requests.

When the nginx queue fills up, the application container cannot accept any more requests. We could increase the nginx queue above 100, but it would only mask the problem. At some point, it's better to turn away requests and serve those already in line. Refer to Overloaded Workers for more information.

This error can be caused by sustained spikes in traffic (often caused by search engine crawlers) and by having PHP processes that run too slowly or have long waiting times for external resources which occupy the application container for long periods. Consider upgrading your site plan if you have too much traffic for your site's resources.

Pantheon 504 Gateway Timeout

The application did not respond in time.

There are two possible causes for this error. Pantheon's routing and caching layer can only sustain open HTTP requests for a set time period. You may encounter this message if your application takes too long to respond. The other option is that there was an application problem, resulting in php-fpm or MySQL timing out. Refer to Timeouts on Pantheon for more information.

Typically the request timeout is much shorter than the hard timeout for PHP. While you may be able to let an operation run for several minutes in your local development environment, this isn't possible on Pantheon. However, there are ways to solve the problem. There are many things that could cause your site to exceed the request timeout limit. The first step to fixing any problem is to identify the root cause. Refer to Timeouts on Pantheon for troubleshooting tips, and consider using New Relic to monitor and improve your site performance.

Pantheon 504 Target in Maintenance

The web site you were looking for is currently undergoing maintenance.

This is not a web application (WordPress or Drupal) maintenance mode error. This is a manually toggled emergency message reserved for unusual circumstances when a site is known to be unavailable.

Error 561 No site Detected

No site detected. Make sure your code is pulled into this environment.

This error typically occurs when a site has been created, but no CMS has been installed. You will also see this error instead of a 403 Directory listing denied error, if you have no index file.

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