[Solved] Big File Size: Cannot upload file through Nginx Error 500

Reference: https://ofstack.com/Nginx/17070/nginx-upload-file-size-error-500-solution.html

TL:DR; Add `client_body_buffer_size 100M;` in nginx.conf, besides client_max_body_size, then restart nginx.

--

 The symptoms are as follow:

  • We have an Nginx server that routes traffic to internal Wordpress CMS
  • When user uploads file through media page in WP, only file in small size (< 10K) can be uploaded, while file with large size (e.g. > 1M and <= 2M) cannot be uploaded.
    • The error is: "Post-processing of the image failed likely because the server is busy or does not have enough resources. Uploading a smaller image may help. Suggested maximum size is 2500 pixels."
    • Strictly speaking, this is a PHP image library error, not WP error.  You cannot find this error in WP source code
    • WP is hosted on Apache server.
    • PHP post size, max size is setting to 80M (or any other large values) in php.ini.
    • Nginx client client_max_body_size is set to 10M (or any other large value)
  • No error logs
    • WP did not create any error_log regarding this, as when big file is dragged to WP, it can't even "touch" WP and Nginx "immediately" produce 500 error
      • Not "timeout", the 500 error is returned immediately
    • No PHP error (since haven't touch WP at all), no wp-content/debug.log
    • No Apache error (error_log, access_log)
    • No Nginx log
      • This is the most weird thing...
      • Nginx error_log regarding the upload is completely "empty"
        • No log related to upload
      • Nginx access_log is also "empty"
      • The error 500 is confirmed coming from Nginx!
Solution:
  • Thanks to our colleague, the above reference shed a light on the actual, core problem.
  • While we think that using `client_max_body_size` seems enough, it is not
  • You need to also add `client_body_buffer_size` also, which is not defined by default in our nginx.conf
    • Not sure if other version of Nginx has this config, in our case, we did not see that, even in conf.d/
  • So our config include BOTH: 
    • `client_max_body_size 100M;` AND 
    • `client_body_buffer_size 100M;`
  • After restarting Nginx, upload is fine again.
    • We tested using a 5MB image and it is uploaded successfully.
Notes:
  • We did not define client_body_temp_path in nginx.conf
    • As long as everything works, keep it untouch/as it is
  • Suppose both client_*_size is defined in nginx.conf under `server{}` section
    • It is how I did.
  • Lesson learnt: Actually we should be able to identify, if we think more deeply:
    • Nginx returns error 500
    • Nginx did not produce any error_log
    • Given the above two points, the problem lies in "Nginx" and everything in front of Nginx (e.g. Firewall, load balancer)
      • We have people checking on Firewall and load balancer, no trace, no log
    • Since there is "No error", we should be able to identify that it is a config issue
    • We believe and without checking that Nginx has already had all the configs, which is wrong
Hope it helps someone and save someone's lives ~~

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