nginx resource temporarily unavailable and 502

if you get 502 errors in nginx and

connect() to unix:/var/run/php-fpm/php-fpm.sock failed (11: Resource temporarily unavailable) while connecting to upstream in the site's nginx error file

a possible fix could be changing from unix sockets to tcp sockets.

in nginx site conf file:
fastcgi_pass    127.0.0.1:9000;

and

in the php-fpm conf file:
listen = 127.0.0.1:9000