[Solved] Drupal cannot upload large files

Drupal is a popular, open-source content management system (CMS) that allows users to build and manage dynamic websites, web applications, and online content. It provides a flexible and robust framework for creating websites with customizable features and functionalities.

1. Setup:We have the following setup. On front we have AWS ALB and on the backend we have nginx and php-fpm services running inside the containers. Also, on another container we have php container where we have drupal sites.
2. Issue: We recently had an issue while uploading the large audio files to a Drupal site. Uploading the files upto 35MB worked but the size greater than that did not work.
3. Things we tried: We tried to investigate the issue by setting higher upload, timeout and memory limits on both nginx and php-fpm configurations.
4. Error we got: Nothing in nginx and php-fpm logs. But on the chrome console we got the below error.

   POST http://sitename/admin/add/test?element_parents=formfile&ajax_form=1&_wrapper_format=drupal_ajax&_wrapper_format=drupal_ajax HTTP/1.1" 400

5. Nginx configurations we had:

       client_max_body_size 200M;
       client_body_buffer_size 200M;
       types_hash_max_size 2048;
       client_header_buffer_size 4k;
       large_client_header_buffers 4 16k;
       ## Needed for the PCI
       server_tokens off;
       ## This is for the configuration files. Nginx will tell you when it needs this increased.
       server_names_hash_bucket_size 512

6. Troubleshooting:
   After wasting our time for 2 days, we were finally got the breakthrough. The culprit was the client_body_buffer_size setting. It was set to 200MB.
7. Explanation:
   Basically, the buffer was too big and nginx was not able to allocate so much memory for keeping the file inside it. We had to lower the buffer to a normal value, so that file is buffered to a temp file during upload and things worked as expected from thereon.
8. Conclusion:
   And thus "Nginx cannot upload large files - 502 Gateway timeout" was solved by setting the client_body_buffer_size value to 128K.
   
   Hope this documentation helps!!!!
   
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