503 status when serving many concurrent files

Thanks for making powprox, it's made development easier for me. Unfortunately I'm currently running into some issues which I've traced down to powprox. I'm running osx 10.11.4.

Accessing the .dev domain with http it works, but with https some of the "later" resources (such as `@import`s in css files & images) fail with a 503 result. The images & css files aren't big (< 1MB), and there are only about 20 total requests, of which ~6 fail.

I've updated the nginx config to write an error log, in which the following message matches requests returning 503: `an upstream response is buffered to a temporary file /usr/local/var/run/nginx/proxy_temp/1/16/0000000161 while reading upstream`. I tried applying various fixes I found online to no avail.

The requests in question - I'm looking in the browser's network inspector - have the same request headers, but fewer response headers, specifically: `status: 503`, `server: nginx/1.10.2`, date, content-type, and `x-pow-template:application_not_found`. My guess is that the proxy configuration isn't setup to handle file buffered responses, but I'm not sure how to verify or resolve it.

I installed powprox in August, and am not sure how to update or uninstall it.

Thanks,
Magnus

Start with the nginx configuration and the error-log entry showing an upstream response buffered to a temporary file, then reproduce the concurrent HTTPS requests in the browser network inspector. Compare successful and 503 responses, and consider the issue done when the affected CSS imports and images are served successfully under the same request load.

Written by the indexing model from the issue text.