nginx反向代理设置，768 worker_connections在连接上游时是不够的

Question

我正在nginx上设置反向代理。 我有一个使用server_name phpmyadmin.lvh.me的虚拟主机设置，我想将localhost/phpmyadmin重定向到phpmyadmin.lvh.me作为反向代理。

这是我的默认配置文件：

upstream phpmyadmin {
    server phpmyadmin.lvh.me:80;
}

server {
    listen 80 default_server;
    listen [::]:80 default_server ipv6only=on;

    root /usr/share/nginx/html;
    index index.html index.htm;

    # Make site accessible from http://localhost/
    server_name localhost;

    location /phpmyadmin/ {
        proxy_pass http://phpmyadmin;
    }

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ =404;
        # Uncomment to enable naxsi on this location
        # include /etc/nginx/naxsi.rules
    }

    # Only for nginx-naxsi used with nginx-naxsi-ui : process denied requests
    #location /RequestDenied {
    #   proxy_pass http://127.0.0.1:8080;    
    #}

    #error_page 404 /404.html;

    # redirect server error pages to the static page /50x.html
    #
    #error_page 500 502 503 504 /50x.html;
    #location = /50x.html {
    #   root /usr/share/nginx/html;
    #}

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    location ~ \.php$ {
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        # NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini

        # With php5-cgi alone:
        #fastcgi_pass 127.0.0.1:9000;
        # With php5-fpm:
        fastcgi_pass unix:/var/run/php5-fpm.sock;
        fastcgi_index index.php;
        include fastcgi_params;
    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    #location ~ /\.ht {
    #   deny all;
    #}
}

但是当我尝试访问localhost/phpmyadmin时，它会抛出内部服务器错误并显示错误消息：

2015/02/08 22:13:21 [alert] 19470#0: *2293 768 worker_connections are not enough while connecting to upstream, client: 127.0.0.1, server: localhost, request: "GET /phpmyadmin/ HTTP/1.0", upstream: "http://127.0.0.1:80/phpmyadmin/", host: "phpmyadmin"

phpmyadmin.lvh.me的配置写在site-available目录中的不同conf文件中。