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I have a 2GB VPS on DigitalOcean and I am hosting WordPress 3.9.1 under Debian 7 with NGINX, php-fpm and unix socket.
It was working perfectly until last week it started showing a "502 bad gateway" error. I checked the logs and found that:
php5-fpm log is showing pm.max_children was reached and nginx log is showing the following:
[error] 3239#0: *15188 connect() to unix:/var/run/php5-fpm.sock failed (11: Resource temporarily unavailable) while connecting to upstream, client: xxx.xxx.xxx.xxx, server: my.domain, request: "POST /xmlrpc.php HTTP/1.0", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "xxx.xxx.xxx.xxx"
I manually changed pm with different settings with no luck. I always restart the daemons after every change.
pm settings are:
pm = dynamic
pm.max_children = 100
pm.start_servers = 10
pm.min_spare_servers = 10
pm.max_spare_servers = 10
pm.max_requests = 200
www.conf has the listen = /var/run/php5-fpm.sock enabled.
Anyone with a similar experience?
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First open the php-fpm configuration file and enable the status page as shown. Inside this file, find and uncomment the variable pm. status_path = /status as shown in the screenshot. Save the changes and exit the file.
PHP-FPM (FastCGI Process Manager) is an alternative to FastCGI implementation of PHP with some additional features useful for sites with high traffic. It is the preferred method of processing PHP pages with NGINX and is faster than traditional CGI based methods such as SUPHP or mod_php for running a PHP script.
For example, on CentOS 8, with a single version, all PHP configuration files are located in the /etc directory and the default PHP-FPM pool (www) configuration file is /etc/php-fpm.
The first problem is you are specifying 100 max_children, that is awfully high for 2GB. I would drop it to 25 children. See my post here on how to optimise your php-fpm configuration for your setup:
WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning
Also, using unix sockets is slightly faster since it provides you direct network access without any TCP/IP overhead. On the down side, it is not as scalable as TCP/IP. Nginx will throw 502 errors when the sockets have been depleted. In such a case you can either tweak the OS settings to accommodate the larger connection pool or just switch to switch to TCP/IP.
In your fastcgi conf change:
fastcgi_pass unix:/var/run/php5-fpm.sock;
to:
fastcgi_pass 127.0.0.1:9000;
Note that port 9000 is the default port set in php-fpm, if you have changed php-fpm to listen on another port then swap 9000 with that value. Make sure you restart both php-fpm and nginx.
Now, if after all of this, you still cannot get it to work and free -m returns high memory usage, then it is time to add more ram to your server.
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