Intermittent 504 gateway timeout on requests

[alexgibson]

Sometimes when hitting a Basket API endpoint I'm seeing a 504 GATEWAY_TIMEOUT. It seems totally random and not based on a specific request made. It appears to happen rarely, but I've now seen it a handful of times so thought I should file a bug.

Example error:

https://basket.mozilla.org/news/newsletters/
[HTTP/1.1 504 GATEWAY_TIMEOUT 291ms]

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://basket.mozilla.org/news/newsletters/. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 504.