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php-cgi进程数不够用、php执行时间长、或者是php-cgi进程死掉，都会出现502错误.

solution:

• KeepAliveTimeout 15
• TimeOut 300 (required)
• http
  {
  fastcgi_connect_timeout 300;
  fastcgi_send_timeout 300;
  fastcgi_read_timeout 300;
  } (For fastcgi)
• max_execution_time 300 (php.ini)

netstat -anpo | grep “php-cgi” | wc -l 查看当前的PHP FastCGI进程数是否够用.如果实际使用的“FastCGI进程数”接近预设的“FastCGI进程数”，那么，说明“FastCGI进程数”不够用，需要增大。