The /var/log/nginx/error.log last lines with me is:
2017/11/03 15:32:31 [error] 11344#11344: *8081 connect() to unix:/var/run/php/php7.0-fpm.sock failed (11: Resource temporarily unavailable) while connecting to upstream, client: 188.8.131.52, server: ubuntufacile.tk, request: $
I can deduct that it is realy a php-fpm communication failed.
So, I try to change the FastCgi request path wich was "/run/php/php7.0-fpm.sock" in the file /etc/php/7.0/fpm/pool.d/www-conf by "127.0.0.1:9000" and do the same with the fastcgi parameter in my vhosts conf files. Then, i reload php-fpm and nginx service and my sites are back again.
in the /etc/php/7.0/fpm/pool.d/www-conf:
Comment this line with (;) prefixe
;listen = /run/php/php7.0-fpm.sock
then add bellow
listen = 127.0.0.1:9000;
Then, in the site conf file, (/etc/nginx/sites-available/)
Comment this line with (#) prefixe
then add bellow the line
I hope just it is fix for ever despite of an futur packages upgrade, because, i'd try the same method before without success, reason for my previous apt purge and reinstall. Although, i used a single different socket php-fpm pool for each site/vhost before have the trouble lastly. It worked kindly during several months.
Sorry for my english.. I'm french speaker