最近网站刷新后经常出现503 Service Temporarily Unavailable错误，有时有可以，联想到最近在nginx.conf里做了单ip访问次数限制，(limit_req_zone $binary_remote_addr zone=allips:20m rate=20r/s;) 把这个数量放大后在刷新发现问题解决。（还顺便把这个改大了 limit_req zone=allips burst=50 nodelay; ）为了证实该问题，反复改动该数量测试发现问题确实在这。这个数量设得太小有问题，通过fiddler发现web页面刷新一下，因为页面上引用的js,css,图片都算一个连接。所以单个页面刷新下就有可能刷爆这个限制，超过这个限制就会提示503 Service Temporarily Unavailable。

  通过修改 Nginx 的配置文件 nginx.conf 实现：

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#user nobody;
worker_processes 1;
#worker_rlimit_nofile 100000; 
#error_log logs/error.log;
#error_log logs/error.log notice;
#error_log logs/error.log info;
  
#pid    logs/nginx.pid;
  
events {
  worker_connections 1024;
}
  
http {
  include    mime.types;
  default_type application/octet-stream;
  
##cache##
 proxy_connect_timeout 5;
 proxy_read_timeout 60;
 proxy_send_timeout 5;
 proxy_buffer_size 16k;
 proxy_buffers 4 64k;
 proxy_busy_buffers_size 128k;
 proxy_temp_file_write_size 128k;
 proxy_temp_path /home/temp_dir;
 proxy_cache_path /usr/local/nginx/cache levels=1:2     keys_zone=cache_one:200m inactive=1d max_size=30g;
 ##end##
#limit per ip per second access times 10 
limit_req_zone $binary_remote_addr zone=allips:20m rate=20r/s;
  
  #log_format main '$remote_addr - $remote_user [$time_local] "$request" '
  #         '$status $body_bytes_sent "$http_referer" '
  #         '"$http_user_agent" "$http_x_forwarded_for"';
  
  #access_log logs/access.log main;
  
  sendfile    on;
  #tcp_nopush   on;
  
  #keepalive_timeout 0;
  keepalive_timeout 65;
  
  #gzip on;
upstream myweb80{
  ip_hash;
  server 192.168.3.105:80;
  server 192.168.3.103:80;
}
  
upstream myweb8080{
  ip_hash;
  server 192.168.3.222:10080;
  #server 192.168.3.103:8080;
 } 
upstream myweb10086{
  ip_hash;
  server 192.168.3.102:10086;
  server 192.168.3.108:10086;
 } 
upstream myweb443{
  ip_hash;
  server 192.168.3.105:443;
  server 192.168.3.103:443;
 } 
  
  # another virtual host using mix of IP-, name-, and port-based     configuration
  #
  server {
    listen    80;
    allow  218.17.158.2;
allow 127.0.0.0/24;
allow 192.168.0.0/16;
allow 58.251.130.1;
allow 183.239.167.3;
allow 61.145.164.1;
deny  all;
server_name myweb.com;
    location / {
        proxy_pass http://myweb80;
proxy_set_header X-Real-IP $remote_addr;
limit_req zone=allips burst=50 nodelay;  
    }
  }
  
  server {
    listen    8080;
allow  218.17.158.2;
allow 127.0.0.0/24;
allow 192.168.0.0/16;
allow 58.251.130.1;
allow 183.239.167.3;
allow 61.145.164.1;
deny  all;
    location / {
        proxy_pass http://myweb8080;
proxy_set_header X-Real-IP $remote_addr;
limit_req zone=allips burst=50 nodelay;  
    }
  }
  
# HTTPS server
  #
  server {
    listen    10086 ssl;
    server_name localhost;
allow  218.17.158.2;
allow 127.0.0.0/24;
allow 192.168.0.0/16;
allow 58.251.130.1;
allow 183.239.167.3;
allow 61.145.164.1;
#deny  all;
    ssl_certificate   ssl/1_www.myweb.com_bundle.crt;
    ssl_certificate_key ssl/2_www.myweb.com.key;
  
  #  ssl_session_cache  shared:SSL:1m;
  #  ssl_session_timeout 5m;
  
  #  ssl_ciphers HIGH:!aNULL:!MD5;
  #  ssl_prefer_server_ciphers on;
  
    location / { 
   proxy_pass https：// myweb10086; 
   #roft html; 
   #index index.html index.htm; 
    } 
  }
  
  服务器{ 
    listen 443 ssl; 
    server_name localhost;
  
    ssl_certificate ssl / 1_www.myweb.com_bundle.crt; 
    ssl_certificate_key ssl / 2_www.myweb.com.key;
  
  #ssl_session_cache共享：SSL：1m; 
  #ssl_session_timeout 5m;
  
  #ssl_ciphers HIGH：！aNULL：！MD5; 
  #ssl_prefer_server_ciphers on;
  
    location / { 
   proxy_pass https：// myweb443; 
   #roft html; 
   #roft html; 
   #index index.html index.htm; 
    } 
  } 
}