使用php-fpm，Nginx上的活动请求急剧增加

突然，今天上午10点左右，Nginx的活跃客户端请求数量急剧增加。

http://gyazo.com/a34263e00065b2c52d03b0c295b5cfa3

随着活动请求的增加，服务器的cpu使用率也会增加，并返回错误的响应。

http://gyazo.com/28ff3e4cfe73ebbc76eb74f225d91d3d

请教我在我的环境中发生了什么。

我的环境很低：

亚马逊ELB<->Nginx（版本1.4.3）<->php fpm（5.4.23版）<->WordPress（版本3.9.2）<->MySQL（第5.5.31版）

/etc/nginx/conf.d/default.conf：

server {
    listen      80 default;
    server_name example.com;
    root        /var/www/vhosts/example;
    index       index.html index.htm;
    charset     utf-8;
    access_log  /var/log/nginx/access.log  main;
    error_log   /var/log/nginx/error.log;
    include     /etc/nginx/drop;
    rewrite /wp-admin$ $scheme://$host$uri/ permanent;
    set $mobile '';
    location ~* ^/wp-(content|admin|includes) {
        index   index.php index.html index.htm;
        if ($request_filename ~ .*'.php) {
            break;
            proxy_pass http://backend;
        }
        include /etc/nginx/expires;
    }
    location / {
        if ($request_filename ~ .*'.php) {
            break;
            proxy_pass http://backend;
        }
        include /etc/nginx/expires;
        set $do_not_cache 0;
        if ($http_cookie ~* "comment_author_|wordpress_(?!test_cookie)|wp-postpass_" ) {
            set $do_not_cache 1;
        }
        if ($request_method = POST) {
            set $do_not_cache 1;
        }
        proxy_no_cache     $do_not_cache;
        proxy_cache_bypass $do_not_cache;
        proxy_redirect     off;
        proxy_cache        czone;
        proxy_cache_key    "$scheme://$host$request_uri$mobile";
        proxy_cache_valid  200 0m;
        proxy_pass http://backend;
    }
}
server {
    listen      unix:/var/run/nginx-backend.sock default;
    server_name _;
    root        /var/www/vhosts/example;
    index       index.php index.html index.htm;
    access_log  /var/log/nginx/backend.access.log backend;
    keepalive_timeout 25;
    port_in_redirect  off;
    gzip              off;
    gzip_vary         off;
    include /etc/nginx/wp-multisite-subdir;
}

/etc/php-fpm.d/www.conf:

[www]
listen = /var/run/php-fpm.sock
listen.owner = nginx
listen.group = nginx
listen.mode = 0666
user = nginx
group = nginx
pm = dynamic
pm.max_children = 15
pm.start_servers = 1
pm.min_spare_servers = 1
pm.max_spare_servers = 4
pm.max_requests = 200
rlimit_files = 131072
rlimit_core = unlimited
request_terminate_timeout = 90
request_slowlog_timeout = 60
slowlog = /var/log/php-fpm/www-slow.log
php_admin_value[error_log] = /var/log/php-fpm/www-error.log
php_admin_flag[log_errors] = on
php_admin_value[upload_max_filesize] = 64M
php_admin_value[post_max_size] = 64M
php_admin_value[max_execution_time] = 60

服务器规格：

$ uname -a
Linux ip-172-31-1-34 3.4.82-69.112.amzn1.x86_64 #1 SMP Mon Feb 24 16:31:21 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$ cat /etc/system-release
Amazon Linux AMI release 2013.09