nginx – 上传超时(110：连接超时)静态内容？

我有一种情况,其中两个网络服务器设置为nginx作为负载平衡器,并且是后端本身.发行版是Debian Wheezy.两台服务器上的配置相同(四核与32GB内存)

TCP

#/etc/sysctl.conf
vm.swappiness=0
net.ipv4.tcp_window_scaling=1
net.ipv4.tcp_timestamps=1
net.ipv4.tcp_sack=1
net.ipv4.ip_local_port_range=2000 65535
net.ipv4.tcp_max_syn_backlog=65535
net.core.somaxconn=65535
net.ipv4.tcp_max_tw_buckets=2000000
net.core.netdev_max_backlog=65535
net.ipv4.tcp_rfc1337=1
net.ipv4.tcp_fin_timeout=5
net.ipv4.tcp_keepalive_intvl=15
net.ipv4.tcp_keepalive_probes=5
net.core.rmem_default=8388608
net.core.rmem_max=16777216
net.core.wmem_max=16777216
net.ipv4.tcp_rmem=4096 87380 16777216
net.ipv4.tcp_wmem=4096 16384 16777216
net.ipv4.tcp_congestion_control=cubic
net.ipv4.tcp_tw_reuse=1
fs.file-max=3000000

Nginx的

#/etc/nginx/nginx.conf
user www-data www-data;
worker_processes 8;
worker_rlimit_nofile 300000;
pid /run/nginx.pid;

events {
        worker_connections 8192;
        use epoll;
        #multi_accept on;
}
http {
        sendfile on;
        tcp_nopush on;
        tcp_nodelay on;
        keepalive_timeout 10;
        types_hash_max_size 2048;
        server_tokens off;

        open_file_cache max=200000 inactive=20s;
        open_file_cache_valid 30s;
        open_file_cache_min_uses 5;
        open_file_cache_errors on;

        gzip on;
        gzip_vary on;
        gzip_proxied any;
        gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;
        gzip_min_length 10240;
        gzip_disable "MSIE [1-6].";
}

server {
    listen 

ab -c 200 -n 40000 -q https://www.example.com/static/file.html

upstream timed out (110: Connection timed out) while connecting to upstream

# netstat -tan | grep ':8080 ' | awk '{print $6}' | sort | uniq -c
      2 LISTEN
     55 SYN_SENT
  37346 TIME_WAIT

    proxy_http_version 1.1;
    proxy_set_header Connection "";