However, I've noticed that the forum now can hang up a bit at times. While investigating with NewRelic, I've found these hiccups almost always correspond to slow external servers (taking more than 15 seconds to respond) which are being accessed from XenForo's proxy.php. See these graphs from earlier today, for example, which show how a 100-second response from a slow website apparently had a significant impact on all my visitors (I personally received a 504 Nginx timeout error during this incident):
It bothers me that a slow origin server can impact the performance of my entire site, though I'm still a bit surprised that it's happening. How is the image proxy designed to deal with these situations, and is there anything I can do to mitigate it? I'm running Nginx/PHP-FPM on CentOS via @eva2000's Centminmod.