网站 502 解决方法

Nginx 502 Bad Gateway的含义是请求的PHP-CGI已经执行，但是由于某种原因（一般是读取资源的问题）没有执行完毕而导致PHP-CGI进程终止。
Nginx 504 Gateway Time-out的含义是所请求的网关没有请求到，简单来说就是没有请求到可以执行的PHP-CGI。

出现错误最重要的事查看错误信息；一般错误信息提示能够直接有效的让你找到解决办法。

查看错误日志显示：

[28-Sep-2017 17:31:42] WARNING: [pool www] server reached pm.max_children setting (8), consider raising it[28-Sep-2017 20:18:27] NOTICE: Terminating ...[28-Sep-2017 20:18:27] NOTICE: exiting, bye-bye![28-Sep-2017 20:18:56] NOTICE: fpm is running, pid 1253[28-Sep-2017 20:18:56] NOTICE: ready to handle connections[28-Sep-2017 20:46:05] WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children, there are 0 idle, and 4 total children[28-Sep-2017 23:52:10] WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children, there are 0 idle, and 4 total children[28-Sep-2017 23:52:11] WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 16 children, there are 0 idle, and 5 total children[28-Sep-2017 23:52:12] WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 32 children, there are 0 idle, and 6 total children[28-Sep-2017 23:52:39] WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children, there are 0 idle, and 4 total children

server reached pm.max_children setting (8), consider raising it

提示我们服务器子进程已达最大值 pm.max_children 需要增大该值；

seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 32 children, there are 0 idle, and 6 total children

错误提示需要增大 pm.start_servers 或 pm.min_spare_servers 或 pm.max_spare_servers

; 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.

; 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 = 30          //10 + (50 - 10)/2

经验人士的总结：

一般php-fpm进程占用20~30m左右的内存就按30m算。如果单独跑php-fpm，动态方式起始值可设置物理内存Mem/30M，由于大家一般Nginx、MySQL都在一台机器上，于是预留一半给它们，即php-fpm进程数为$Mem/2/30（单位相同）。

1核2G的服务器配置如下：

pm = dynamicpm.max_children = 50pm.start_servers = 30pm.min_spare_servers = 10pm.max_spare_servers = 50