WARNING: [pool inter] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children,

Question

I have a problem with nginx and php-fpm, i searched already in this form but i found no solution for it.

Server: 16 cores 10gb memory

WARNING: [pool inter] server reached pm.max_children setting (20), consider raising it

[i]
listen = /var/run/fastcgi/i.sock    
listen.allowed_clients = 127.0.0.1    
listen.group = i

user = i

group = inter
pm = dynamic

pm.max_children = 20    
pm.max_requests = 1000

pm.start_servers = 15    
pm.min_spare_servers = 15

pm.max_spare_servers = 15    
;request_terminate_timeout = 300

php_admin_value[error_log] = /var/log/php-fpm/i-error.log    
php_admin_flag[log_errors] = on

php_value[session.save_handler] = files    
php_value[session.save_path] = /var/lib/php/ = /

php_admin_value[open_basedir] = /www/public_html/:/tmp:/usr/share/php:/var/lib/php

strong textphp_admin_value[disable_functions] = dl,exec,passthru,shell_exec,system,proc_open,popen,curl_exec,curl_multi_exec,parse_ini_file,show_source

i tried a lot of differnt settings, but i don't know what is the reason, i hope sombody can help.

Best regards

Answer 1

The issue happen from misconfiguration fpm pool config.

This confusion happen when You delete comments from default config example.


so I'm fixing Your config example with comments from original example file (www.conf).


it should be like:

; Choose how the process manager will control the number of child processes.
; Possible Values:
;   static  - a fixed number (pm.max_children) of child processes;
;   dynamic - the number of child processes are set dynamically based on the
;             following directives. With this process management, there will be
;             always at least 1 children.
;             pm.max_children      - the maximum number of children that can
;                                    be alive at the same time.
;             pm.start_servers     - the number of children created on startup.
;             pm.min_spare_servers - the minimum number of children in 'idle'
;                                    state (waiting to process). If the number
;                                    of 'idle' processes is less than this
;                                    number then some children will be created.
;             pm.max_spare_servers - the maximum number of children in 'idle'
;                                    state (waiting to process). If the number
;                                    of 'idle' processes is greater than this
;                                    number then some children will be killed.
;  ondemand - no children are created at startup. Children will be forked when
;             new requests will connect. The following parameter are used:
;             pm.max_children           - the maximum number of children that
;                                         can be alive at the same time.
;             pm.process_idle_timeout   - The number of seconds after which
;                                         an idle process will be killed.
; Note: This value is mandatory.
pm = dynamic

; The number of child processes to be created when pm is set to 'static' and the
; maximum number of child processes when pm is set to 'dynamic' or 'ondemand'.
; This value sets the limit on the number of simultaneous requests that will be
; served. Equivalent to the ApacheMaxClients directive with mpm_prefork.
; Equivalent to the PHP_FCGI_CHILDREN environment variable in the original PHP
; CGI. The below defaults are based on a server without much resources. Don't
; forget to tweak pm.* to fit your needs.
; Note: Used when pm is set to 'static', 'dynamic' or 'ondemand'
; Note: This value is mandatory.
pm.max_children = 1024    

; The desired minimum number of idle server processes.
; Note: Used only when pm is set to 'dynamic'
; Note: Mandatory when pm is set to 'dynamic'
pm.min_spare_servers = 16

; The desired maximum number of idle server processes.
; Note: Used only when pm is set to 'dynamic'
; Note: Mandatory when pm is set to 'dynamic'
pm.max_spare_servers = 64  

; The number of child processes created on startup.
; Note: Used only when pm is set to 'dynamic'
; Default Value: min_spare_servers + (max_spare_servers - min_spare_servers) / 2
pm.start_servers = 40

pm.max_requests = 32 ; to avoid memory leaks it's better respawn child after 32 request

personally I don't like idle processes.
I just set:

pm = ondemand
pm.max_children = 1024 
pm.process_idle_timeout = 10s

Full example file with comments that explains
what is the meaning concrete param
You can see from here: https://gist.github.com/num8er/43ae78ee6404b12db799946616c36251

Answer 2

The root cause of your problem can't be determined because we don't know what kind of code your server runs.

What happens is that PHP can't process requests fast enough to keep up with nginx.

Raising number of child processes won't help, you have 16 cores and 20 processes. This means that your OS will be forced to schedule processes and raising the number won't make anything faster - you don't even know if you are CPU or I/O bound.

To correctly solve this problem, you need to determine why PHP can't keep up.

You can enable PHP-FPM slow_log feature by adding this to your pool:

slowlog = /var/log/php-fpm/slow.log
request_slowlog_timeout = 1s

This will log every request that took 1 second or longer to file /var/log/php-fpm/slow.log

Inspect the log file and trace back which part of your code causes PHP to respond slowly and fix the real problem

---

To keep your site responsive until you fix the real problem is that you get another server for PHP processing. Since you are using nginx and php-fpm is your backend, then it's quite trivial to set up more servers to handle dynamic request processing. As your site grows and demands grow with it, you can easily add more backend processing power by adding php-fpm serves to processing pool.

Disclaimer: I am not saying that you should but it's good to know what your options are.

Example configuration file for nginx for multiple PHP backends

    # Define servers in the cluster
    upstream phpcluster {
        server 10.0.0.1:9000;
        server 10.0.0.2:9000;
    }

    location ~ \.php$ {
        try_files                   $uri /index.php =404;
        fastcgi_split_path_info     ^(.+\.php)(/.+)$;
        fastcgi_pass                phpcluster; # Pass to phpcluster upstream. Additional load balancing rules can be defined in upstream block
        fastcgi_index               index.php;
        fastcgi_param               SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }  

Answer 3

Increase the number in pm.max_children. 20 is too low.