On a wordpress site, we have requests coming in to CloudFront, which sends the request to origin (if necessary) which goes through an ELB, and to two or three instances that will service the request.
Most requests work, but when we upload a JSON file to admin-ajax.php, it results in a 504 error that we captured from the CloudFront logs:
2022-01-31 21:32:24 MIA3-C2 1462 67.190.247.197 POST d2q8ixmwt0jy43.cloudfront.net /wp-admin/admin-ajax.php 504 https://xxxxxxx.com/wp-admin/edit.php?post_type=elementor_library&tabs_group=library Mozilla/5.0%20(Windows%20NT%2010.0;%20Win64;%20x64)%20AppleWebKit/537.36%20(KHTML,%20like%20Gecko)%20Chrome/97.0.4692.99%20Safari/537.36%20Edg/97.0.1072.76 - - Error Ae0gLzThCiZR2N5D8gLO6s-o8IwwlmYrxWvUbUgr1A64_nMpzN0qRg== evolvetelemed.com https 167737 30.107 - TLSv1.3 TLS_AES_128_GCM_SHA256 Error HTTP/2.0 - - 64798 30.107 OriginCommError text/html 1033 - -
The error appears to be an OriginCommError, but I cannot see why it is getting that error. Tailing the logs on our web servers on the instances shows that the request is not even reaching there.
I am not exactly sure why some requests would work and some wouldn't. To add further conclusion, when binary files in the media library are uploaded to async-upload.php, it works.
We use nginx as a webserver on the front end using php-fpm for processing php.
