I moved hosting of roughly 150 Wordpress sites from Apache/mod_php to Nginx/php-fpm after having tested and found measurably better performance with Nginx. (hosted on Centos 6/7) The first problem I ran into was that the server ran completely out of memory (30GB of RAM) and came to a complete crash one night, I presume when all the bots came by -- never hard this issue before. I changed from static pm to ondemand, with 10 and 25 children per pool max, each website has it's own pool. The new problem is that I start getting bad gateway errors just as regularly, as if there's no queuing of new requests. I get frequent lockups where it would seem that somehow every child in every pool is in use, and there is no queuing of requests from Nginx to php-fpm, and this state is maintained until I restart php-fpm There are no errors in besides infrequent "unable to read what child say: Bad file descriptor" which is pretty vague. This is currently on Centos 7 64bit with Nginx 1.6.0 (from nginx's repos) and php-fpm 5.5.15 (from the Remi repos)
