Drupal 8 Render Pipeline for Newbies
BY webmaster
4 years ago

Authors: Adrian McDonald Tariang, Anish M.M.

Drupal 8 Render Pipeline is the sequence of steps through which Drupal 8 generates a response to an HTTP request. ie, it’s what’s going on under the hood of Drupal 8.

As summer interns, we were trying to understand this process. While going through online material available on the topic, we noted that almost half of it was aimed at people transitioning from Drupal 7 to Drupal 8. Newbies as were to Drupal, we did struggle to figure it out. While digging through the material, it is quite easy to be misled and arrive at wrong conclusions. So, we have come up with this presentation, which targets beginners and keeps it as simple as possible.

This presentation is a walk through of the steps followed by Drupal 8 between getting a request and sending back the corresponding response, in that order, with specific details and examples mentioned when deemed necessary. It will provide an overview of the whole process, with emphasis on the Event Mechanism and the Routing Process.

The presentation will, we hope, give you a broad understanding of the topic and give you pointers on areas to focus. You are encouraged to follow up on this presentation by going through the references mentioned at the end. We cannot emphasize enough the benefits of going through the code, and urge you to download Drupal 8 code and go through it. A little bit of tweaking in there can go a long way in getting to know the concepts. The online documentation of the code will also come in handy.

Few of the tools you could use

  • the blackfire.io or the XHProf profiler, can help in understanding Drupal’s routing system and dependency model
  • debug_backtrace() for local system debugging. The devel module also provides a ddebug_backtrace() that provides a more readable output

In Brief

Drupal 8 adopts most of its functionality from the Symfony Framework to implement modern PHP standards and is a platform for more developers to enter the Drupal Community.

Front Controller

The journey begins at the Front Controller, the index.php file, a construct that serves as an entry and exit point for all communications with Drupal. This is where Drupal wraps the request from the user into a Symfony Response Object for a more object oriented approach for request handling. The Request object is then passed through Symfony’s HttpKernel::handle() method, the backbone of the render pipeline that uses an event-based architecture to delegate the task at hand.

This system makes Drupal easily extensible, as Developers can now create their own Subscribers to events and modify the end response. Drupal 8 uses the concept of a Controller, a section of code which performs the main application logic. The Controller is assigned through a process called Routing, where, each path( say /admin), is mapped to its corresponding controller.


The Controller returns its results in the form of a Response object, ready to be sent back to the user, or a classic Drupal Render Array.

This Render Array is then pushed to the MainContentViewSubscriber, which decides how the array is to be converted into the Response object. This process, called Rendering, is performed by a Content Renderer, based on the format the response needs to be sent in.

Now, when a Response Object is received, Drupal prepares placeholders present on it’s HTML, so as to allow them to be replaced with content by popular placeholder strategies such as ESI, Big Pipe or SingleFlush, after which the final headers and assets are attached to the Response.

This Response is then sent back to the user, completing its journey through the Render Pipeline.


Wim Leers, author to material such as the render pipeline diagram and the DrupalCon Los Angeles 2015: Drupal 8's render pipeline session. These were extensively referred to for this presentation.








on 01st January 2008 / by webmaster
We have added a few new modules to our site recently. Drupal Technical StumbleThis Sean (not verified) access_time 20 Sep 2021 - 00:18 Hi there, I uploaded the files, enabled the modules to use SU, and now I see the link, but there is no icon... How can I fix this? Thanks, Sean webmaster access_time 20 Sep 2021 - 00:18 In reply to Icon doesn't show by Sean (not verified) What do you see when you view the source? Search for stumblethis_button and you should be able to see the code for the image and the URL. Then you should be able to troubleshoot from there. Juicy Couture Addict (not verified) access_time 20 Sep 2021 - 00:18 thanks for the post. would love to hear more of you. by the way, drupal's really popular nowadays as it has easy and fast features. you agree with me? thanks.

on 16th January 2008 / by webmaster
Most webmasters do not realize this, but a lot of the content on lot of websites can be accessed from multiple URLs. A simple example would be where www.example.com and example.com leads to the same page. This is a fatal mistake in Search Engine Optimization and search engines penalize you for duplicate content. The correct configuration would be where the above two urls will lead you to the same page but example.com will redirect you to www.example.com with a 301 (Moved permanently) status which will not result in search engines penalizing the page. It is very easy to configure 301 redirects using Apache .htaccess file and the process is the same for a Drupal installation also. Drupal Technical Apache htaccess SEO Anonymous (not verified) access_time 20 Sep 2021 - 00:18 Hello. I'm trying to make example.com show as www.example.com, and I'm running into difficulties. I'm on Apache 2.0 and using the following lines in my httpd.conf file: RewriteEngine on RewriteCond %{HTTP_HOST} ^xxxxxxxxxx\.com$ [NC] RewriteRule ^(.*)$ http://www.xxxxxxxxxx.com/$1 [L,R=301] When I go to http://xxxxxxxxxx.com, I get http://www.xxxxxxxxxx.com (as expected). However, when I go to http://xxxxxxxxxx.com/node/1 (it's a Drupal site), I get a 404 thrown and the URL changes to xxxxxxxxxx.com/var/www/drupal/node/1. Same thing with www.xxxxxxxxxx.com/node/1. Any suggestions? I want to run without Drupal's .htaccess file (instead incorporating these calls into my httpd.conf file). webmaster access_time 20 Sep 2021 - 00:18 In reply to Rewrite including filesystem path by Anonymous (not verified) I think the problem is with the base path which results in the redirection to /var/www/ part. The best approach I would think is to start with drupal htaccess and then strip out parts and move to httpd SNVC (not verified) access_time 20 Sep 2021 - 00:18 This is definitely a good guide. Thanks for this. wellyson access_time 20 Sep 2021 - 00:18 This is really nice and helpful.

on 08th February 2008 / by webmaster
Attachment Size slashdotit.tar.gz 173.55 KB Similar to the StumbleThis module that we had created earlier we have created another bookmarking Drupal Technical Slashdotit Shlomi Fish (not verified) access_time 20 Sep 2021 - 00:18 Hi! I'm interested in this module, but Drupal 6.2 complains that it's incompatible with it. Can you please update it or tell me how? Regards, Shlomi Fish shlomifish.org webmaster access_time 20 Sep 2021 - 00:18 In reply to Can you update it for Drupal-6.x? by Shlomi Fish (not verified) Sure we are working on this currently and will post an update soon. Also we will post this module on www.drupal.org as well Cheers Anoop John Team Zyxware Anonymous (not verified) access_time 20 Sep 2021 - 00:18 Hello! Nice Article very interesting, thanks