Nginx+Memcached+Tomcat集群配置实践（Sticky Session）

准备工作

创建一个简单的web应用，名为session。其中有两个页面，分别如下所示：

• 页面login.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
     pageEncoding="UTF-8"%>











     

          

               
用户登录
          
          

               

                    
用户名
                    

               
               

                    
密 码
                    

               
               

                    

                           
                    
               
          
     

• 登录成功页面success.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>










<%
     String userName = (String) request.getSession().getAttribute("userName");
%>

     

          

               

                    当前登录用户：<%=userName %>
               
          
     

还有一个Servlet，负责请求的转发，并设置session数据，如下所示：

package org.shirdrn.cluster.tomcat.servlet;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class LoginSevlet extends HttpServlet {
     private static final long serialVersionUID = 1L;
     private static final Log LOG = LogFactory.getLog(LoginSevlet.class);
    private static Map accountDB = new HashMap();
    static {
         accountDB.put("shirdrn", "123456");
         accountDB.put("admin", "999999");
         accountDB.put("dev", "000888");
         accountDB.put("007", "007007");
    }
   
    public LoginSevlet() {
        super();
    }

     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
          this.doPost(request, response);
     }

     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
          String userName = request.getParameter("userName");
          String password = request.getParameter("password");
          LOG.info("Raw input:userName=" + userName + ",password=" + password);
         
          if(userName!=null && password!=null
                    && accountDB.containsKey(userName)
                    && accountDB.get(userName).equals(password)) {
               LOG.info("Login;status=SUCCESS");
               request.getSession().setAttribute("userName", userName);
               request.getRequestDispatcher("success.jsp").forward(request, response);              
          } else {
               LOG.info("Login;status=FAIL");
               request.getRequestDispatcher("login.jsp").forward(request, response);
          }
     }

}

这里模拟了一个账号数据库，对用户的登录请求进行处理。

最后打成WAR包，部署到Tomcat集群中的每个结点上。

Memcached安装、配置、启动

在Ubuntu系统下，如果没有安装Memcached，可以执行如下命令进行安装：

sudo apt-get install memcached

然后，启动Memcached服务进程，这里，我启动了两个服务进程，分别监听端口11211、11311，启动命令如下所示：

sudo /usr/bin/memcached -m 64 -d -u memcache -p 11211 -l 192.168.1.104 -c 5000 -P /tmp/n1-memcached.pid
sudo /usr/bin/memcached -m 64 -d -u memcache -p 11311 -l 192.168.1.104 -c 5000 -P /tmp/n2-memcached.pid

查询Memcached服务状态：

shirdrn@dev:~/servers/cluster/nginx_tomcat_memcached$ ps -ef | grep memcached
memcache  1578     1  0 Jan25 ?        00:00:00 /usr/bin/memcached -m 64 -p 11211 -u memcache -l 127.0.0.1
memcache  3300     1  0 Jan25 ?        00:00:00 /usr/bin/memcached -m 64 -d -u memcache -p 11211 -l 192.168.1.104 -c 5000 -P /tmp/n1-memcached.pid
memcache  3308     1  0 00:00 ?        00:00:00 /usr/bin/memcached -m 64 -d -u memcache -p 11311 -l 192.168.1.104 -c 5000 -P /tmp/n2-memcached.pid
shirdrn   3318  3095  0 00:00 pts/5    00:00:00 grep --color=auto memcached

Tomcat集群配置

Tomcat集群配置，集群中各个结点通过共享存储在缓存Memcached中session来实现session的共享：如果有一台机器上的Tomcat服务停掉了，对于其他对等服务器上的session数据仍然可以从Memcached缓存中读取，从而不会发生session丢失的问题。

对于满足这种配置的实现方案，可以在 https://code.google.com/p/memcached-session-manager和 https://spymemcached.googlecode.com上下载相关的jar文件。因为基于不同的序列化方案，可以有多种配置方法，下面是选择Javolution序列化框架，需要提供如下库文件：

• https://memcached-session-manager.googlecode.com/files/memcached-session-manager-1.6.3.jar
• https://memcached-session-manager.googlecode.com/files/memcached-session-manager-tc7-1.6.3.jar
• https://memcached-session-manager.googlecode.com/files/msm-javolution-serializer-1.6.2.jar
• http://memcached-session-manager.googlecode.com/svn/maven/javolution/javolution/5.4.3.1/javolution-5.4.3.1.jar
• https://spymemcached.googlecode.com/files/spymemcached-2.8.4.jar

下载上述jar文件，拷贝到$CATALINA_HOME/lib目录下，然后需要配置$CATALINA_HOME/conf/server.xml文件。

Tomcat集群中，每个结点的$CATALINA_HOME/conf/server.xml基本配置都是相同的，不同配置内容分别如下：

• 如果在同一台机器上，要保证各个服务端口不相冲突
• 元素中failoverNodes属性值不同

例如，我们在同一台机器上配置了两个Tomcat服务器实例，所在目录分别为tomcat-1和tomcat-2，对应的conf/server.xml配置内容如下：

• tomcat-1/conf/server.xml

这里面，failover的Memcached结点是n1，也就是说，如果tomcat-1和n1在同一台机器上的话，session数据会优先复制到存储到Memcached结点n2，这样即使n1所在的结点宕机了，n2所在结点仍然存储了之前的session数据。

• tomcat-2/conf/server.xml

和上面类似，failover的Memcached结点是n2，也就是说，如果tomcat-2和n2在同一台机器上的话，Session数据会优先复制到存储到Memcached结点n1，这样即使n2所在的结点宕机了，n1所在结点仍然存储了之前的Session数据。

上面的配置实现了Tomcat集群中，通过Memcached实现了Sticky Session（粘性Session），主要是通过配置failover结点来达到目的的。如果采用Non-sticky Session方式，就不需要考虑failover的问题，详细配置扩参考文档（ https://code.google.com/p/memcached-session-manager/wiki/SetupAndConfiguration），下面截取一个片段：

The following example shows a configuration for non-sticky sessions. In this case there's no need for failoverNodes, as sessions are served by all tomcats round-robin and they're not bound to a single tomcat. For non-sticky sessions the configuration (for both/all tomcats) would look like this: ... className="de.javakaffee.web.msm.MemcachedBackupSessionManager" memcachedNodes="n1:host1.yourdomain.com:11211,n2:host2.yourdomain.com:11211" sticky="false" sessionBackupAsync="false" lockingMode="uriPattern:/path1|/path2" requestUriIgnorePattern=".*\.(ico|png|gif|jpg|css|js)$" transcoderFactoryClass="de.javakaffee.web.msm.serializer.kryo.KryoTranscoderFactory" />

分别启动tomcat-1和tomcat-2，如下所示：

shirdrn@dev:~/servers/cluster/nginx_tomcat_memcached$ tomcat-1/bin/catalina.sh start
Using CATALINA_BASE:   /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1
Using CATALINA_HOME:   /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1
Using CATALINA_TMPDIR: /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1/temp
Using JRE_HOME:        /home/hadoop/installation/jdk1.6.0_30
Using CLASSPATH:       /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1/bin/bootstrap.jar:/home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1/bin/tomcat-juli.jar

shirdrn@dev:~/servers/cluster/nginx_tomcat_memcached$ tomcat-2/bin/catalina.sh start
Using CATALINA_BASE:   /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2
Using CATALINA_HOME:   /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2
Using CATALINA_TMPDIR: /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2/temp
Using JRE_HOME:        /home/hadoop/installation/jdk1.6.0_30
Using CLASSPATH:       /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2/bin/bootstrap.jar:/home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2/bin/tomcat-juli.jar

可以查看两个tomcat的启动日志，对比一下：

• tomcat-1的日志

shirdrn@dev:~/servers/cluster/nginx_tomcat_memcached$ tail -100f tomcat-1/logs/catalina.out
Jan 26, 2013 12:03:25 AM org.apache.catalina.core.AprLifecycleListener init
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: /home/hadoop/installation/jdk1.6.0_30/jre/lib/i386/client:/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386:/home/hadoop/installation/jdk1.6.0_30/jre/../lib/i386:/usr/java/packages/lib/i386:/lib:/usr/lib
Jan 26, 2013 12:03:26 AM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8088"]
Jan 26, 2013 12:03:26 AM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-bio-8089"]
Jan 26, 2013 12:03:26 AM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 1743 ms
Jan 26, 2013 12:03:26 AM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Catalina
Jan 26, 2013 12:03:26 AM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.26
Jan 26, 2013 12:03:27 AM de.javakaffee.web.msm.MemcachedSessionService startInternal
INFO: MemcachedSessionService starts initialization... (configured nodes definition n1:192.168.1.104:11211,n2:192.168.1.104:11311, failover nodes n1)
2013-01-26 00:03:27.441 INFO net.spy.memcached.MemcachedConnection:  Added {QA sa=/192.168.1.104:11211, #Rops=0, #Wops=0, #iq=0, topRop=null, topWop=null, toWrite=0, interested=0} to connect queue
2013-01-26 00:03:27.442 INFO net.spy.memcached.MemcachedConnection:  Added {QA sa=/192.168.1.104:11311, #Rops=0, #Wops=0, #iq=0, topRop=null, topWop=null, toWrite=0, interested=0} to connect queue
Jan 26, 2013 12:03:27 AM de.javakaffee.web.msm.RequestTrackingHostValve 
INFO: Setting ignorePattern to .*\.(png|gif|jpg|css|js)$
2013-01-26 00:03:27.459 INFO net.spy.memcached.MemcachedConnection:  Connection state changed for sun.nio.ch.SelectionKeyImpl@5b0668
2013-01-26 00:03:27.460 INFO net.spy.memcached.MemcachedConnection:  Connection state changed for sun.nio.ch.SelectionKeyImpl@1d5a0
Jan 26, 2013 12:03:27 AM de.javakaffee.web.msm.MemcachedSessionService setLockingMode
INFO: Setting lockingMode to null
Jan 26, 2013 12:03:27 AM de.javakaffee.web.msm.MemcachedSessionService createTranscoderFactory
INFO: Creating transcoder factory de.javakaffee.web.msm.serializer.javolution.JavolutionTranscoderFactory
Jan 26, 2013 12:03:27 AM de.javakaffee.web.msm.MemcachedSessionService startInternal
INFO: MemcachedSessionService finished initialization, sticky true, operation timeout 1000, with node ids [n2] and failover node ids [n1]
Jan 26, 2013 12:03:27 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1/webapps/host-manager
Jan 26, 2013 12:03:27 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1/webapps/manager
Jan 26, 2013 12:03:27 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1/webapps/docs
Jan 26, 2013 12:03:27 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1/webapps/examples
Jan 26, 2013 12:03:28 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-1/webapps/ROOT
Jan 26, 2013 12:03:28 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-bio-8088"]
Jan 26, 2013 12:03:28 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["ajp-bio-8089"]
Jan 26, 2013 12:03:28 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 1487 ms

• tomcat-2的日志

shirdrn@dev:~/servers/cluster/nginx_tomcat_memcached$ tail -100f tomcat-2/logs/catalina.out
Jan 26, 2013 12:04:34 AM org.apache.catalina.core.AprLifecycleListener init
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: /home/hadoop/installation/jdk1.6.0_30/jre/lib/i386/client:/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386:/home/hadoop/installation/jdk1.6.0_30/jre/../lib/i386:/usr/java/packages/lib/i386:/lib:/usr/lib
Jan 26, 2013 12:04:34 AM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-9088"]
Jan 26, 2013 12:04:34 AM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-bio-9089"]
Jan 26, 2013 12:04:34 AM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 742 ms
Jan 26, 2013 12:04:34 AM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Catalina
Jan 26, 2013 12:04:34 AM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.26
Jan 26, 2013 12:05:07 AM org.apache.catalina.util.SessionIdGenerator createSecureRandom
INFO: Creation of SecureRandom instance for session ID generation using [SHA1PRNG] took [33,094] milliseconds.
Jan 26, 2013 12:05:07 AM de.javakaffee.web.msm.MemcachedSessionService startInternal
INFO: MemcachedSessionService starts initialization... (configured nodes definition n1:192.168.1.104:11211,n2:192.168.1.104:11311, failover nodes n2)
2013-01-26 00:05:07.873 INFO net.spy.memcached.MemcachedConnection:  Added {QA sa=/192.168.1.104:11211, #Rops=0, #Wops=0, #iq=0, topRop=null, topWop=null, toWrite=0, interested=0} to connect queue
2013-01-26 00:05:07.876 INFO net.spy.memcached.MemcachedConnection:  Added {QA sa=/192.168.1.104:11311, #Rops=0, #Wops=0, #iq=0, topRop=null, topWop=null, toWrite=0, interested=0} to connect queue
Jan 26, 2013 12:05:07 AM de.javakaffee.web.msm.RequestTrackingHostValve 
INFO: Setting ignorePattern to .*\.(png|gif|jpg|css|js)$
2013-01-26 00:05:07.896 INFO net.spy.memcached.MemcachedConnection:  Connection state changed for sun.nio.ch.SelectionKeyImpl@701a27
2013-01-26 00:05:07.897 INFO net.spy.memcached.MemcachedConnection:  Connection state changed for sun.nio.ch.SelectionKeyImpl@1d5a0
Jan 26, 2013 12:05:07 AM de.javakaffee.web.msm.MemcachedSessionService setLockingMode
INFO: Setting lockingMode to null
Jan 26, 2013 12:05:07 AM de.javakaffee.web.msm.MemcachedSessionService createTranscoderFactory
INFO: Creating transcoder factory de.javakaffee.web.msm.serializer.javolution.JavolutionTranscoderFactory
Jan 26, 2013 12:05:07 AM de.javakaffee.web.msm.MemcachedSessionService startInternal
INFO: MemcachedSessionService finished initialization, sticky true, operation timeout 1000, with node ids [n1] and failover node ids [n2]
Jan 26, 2013 12:05:08 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2/webapps/host-manager
Jan 26, 2013 12:05:08 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2/webapps/manager
Jan 26, 2013 12:05:08 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2/webapps/docs
Jan 26, 2013 12:05:08 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2/webapps/examples
Jan 26, 2013 12:05:08 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory /home/shirdrn/servers/cluster/nginx_tomcat_memcached/tomcat-2/webapps/ROOT
Jan 26, 2013 12:05:08 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-bio-9088"]
Jan 26, 2013 12:05:08 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["ajp-bio-9089"]
Jan 26, 2013 12:05:08 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 34163 ms

已经成功启动了。

Nginx安装、配置、启动

在Ubuntu系统下，如果没有安装Nginx，可以执行如下命令进行安装：

sudo apt-get install nginx

默认情况下，Nginx使用默认的配置文件/etc/nginx/nginx.conf，该配置文件直接包含了虚拟目录配置文件/etc/nginx/sites-available/default，修改该文件的内容为，如下所示：

# You may add here your
# server {
#     ...
# }
# statements for each of your virtual hosts to this file

##
# You should look at the following URL's in order to grasp a solid understanding
# of Nginx configuration files in order to fully unleash the power of Nginx.
# http://wiki.nginx.org/Pitfalls
# http://wiki.nginx.org/QuickStart
# http://wiki.nginx.org/Configuration
#
# Generally, you will want to move this file somewhere, and start with a clean
# file but keep this around for reference. Or just disable in sites-enabled.
#
# Please see /usr/share/doc/nginx-doc/examples/ for more detailed examples.
##



upstream dev.shirdrn.org {
     server 192.168.1.104:8088 weight=1;
     server 192.168.1.104:9088 weight=1;
}


server {
     #listen   80; ## listen for ipv4; this line is default and implied
     #listen   [::]:80 default ipv6only=on; ## listen for ipv6

     root /usr/share/nginx/www/session;  # session是我们配置的虚拟目录，实际直接指向Tomcat下名为session的web应用
     index index.html index.htm;

     # Make site accessible from http://localhost/
#######     server_name localhost;
     server_name dev.shirdrn.org; # Nginx服务所在主机
     charset utf-8;

     location / {
          proxy_pass     http://dev.shirdrn.org; #直接代理tomcat集群
          proxy_set_header  X-Real-IP  $remote_addr;
          client_max_body_size  100m;



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

     location ~ ^/(WEB-INF)/ { # 禁止访问Tomcat下web应用的WEB-INF目录下的资源
          deny all;
     }

     location /doc/ {
          alias /usr/share/doc/;
          autoindex on;
          allow 127.0.0.1;
          deny all;
     }

     # Only for nginx-naxsi : process denied requests
     #location /RequestDenied {
          # For example, return an error code
          #return 418;
     #}

     #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/www;
     #}

     # 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;
     #}
}


# another virtual host using mix of IP-, name-, and port-based configuration
#
#server {
#     listen 8000;
#     listen somename:8080;
#     server_name somename alias another.alias;
#     root html;
#     index index.html index.htm;
#
#     location / {
#          try_files $uri $uri/ /index.html;
#     }
#}


# HTTPS server
#
#server {
#     listen 443;
#     server_name localhost;
#
#     root html;
#     index index.html index.htm;
#
#     ssl on;
#     ssl_certificate cert.pem;
#     ssl_certificate_key cert.key;
#
#     ssl_session_timeout 5m;
#
#     ssl_protocols SSLv3 TLSv1;
#     ssl_ciphers ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv3:+EXP;
#     ssl_prefer_server_ciphers on;
#
#     location / {
#          try_files $uri $uri/ /index.html;
#     }
#}

上面配置中根目录为/usr/share/nginx/www，因为我们使用到了一个虚拟目录来对应Tomcat下部署的web应用的path，所以需要在/usr/share/nginx/www下面创建这个对应的虚拟目录：

shirdrn@dev:~/servers/cluster/nginx_tomcat_memcached$ sudo mkdir /usr/share/nginx/www/session

最后，可以启动Nginx服务器，执行如下命令：

shirdrn@dev:~$ sudo /etc/init.d/nginx start

查询Nginx服务启动状态：

shirdrn@dev:~/servers/cluster/nginx_tomcat_memcached$ sudo ps -ef | grep nginx
root      3199     1  0 Jan25 ?        00:00:00 nginx: master process /usr/sbin/nginx
www-data  3200  3199  0 Jan25 ?        00:00:00 nginx: worker process
www-data  3201  3199  0 Jan25 ?        00:00:00 nginx: worker process
www-data  3202  3199  0 Jan25 ?        00:00:00 nginx: worker process
www-data  3203  3199  0 Jan25 ?        00:00:00 nginx: worker process
shirdrn   3327  3095  0 00:01 pts/5    00:00:00 grep --color=auto nginx

这是就可以通过Nginx访问（代理）Web应用首页了。

集群验证

上面配置完成，服务都已经启动成功，可以直接请求链接 http://dev.shirdrn.org/session，就会直接访问部署在Tomcat服务器上的Java Web应用，看到登录页面。

使用前面准备的Web应用session中账号数据进行模拟登录，就可以查看Memcached缓存的数据：

• telnet 192.168.1.104 11211

telnet到memcached服务端口，查看缓存统计数据。

shirdrn@dev:~$ telnet 192.168.1.104 11211
Trying 192.168.1.104...
Connected to 192.168.1.104.
Escape character is '^]'.

ERROR
stats
STAT pid 3300
STAT uptime 2148
STAT time 1359131741
STAT version 1.4.13
STAT libevent 2.0.16-stable
STAT pointer_size 32
STAT rusage_user 0.052003
STAT rusage_system 0.084005
STAT curr_connections 7
STAT total_connections 9
STAT connection_structures 8
STAT reserved_fds 20
STAT cmd_get 23
STAT cmd_set 6
STAT cmd_flush 0
STAT cmd_touch 0
STAT get_hits 2
STAT get_misses 21
STAT delete_misses 0
STAT delete_hits 0
STAT incr_misses 0
STAT incr_hits 0
STAT decr_misses 0
STAT decr_hits 0
STAT cas_misses 0
STAT cas_hits 0
STAT cas_badval 0
STAT touch_hits 0
STAT touch_misses 0
STAT auth_cmds 0
STAT auth_errors 0
STAT bytes_read 2675
STAT bytes_written 2835
STAT limit_maxbytes 67108864
STAT accepting_conns 1
STAT listen_disabled_num 0
STAT threads 4
STAT conn_yields 0
STAT hash_power_level 16
STAT hash_bytes 262144
STAT hash_is_expanding 0
STAT expired_unfetched 0
STAT evicted_unfetched 0
STAT bytes 858
STAT curr_items 2
STAT total_items 6
STAT evictions 0
STAT reclaimed 0
END

• telnet 192.168.1.104 11311

shirdrn@dev:~$ telnet 192.168.1.104 11311
Trying 192.168.1.104...
Connected to 192.168.1.104.
Escape character is '^]'.
stats
STAT pid 3308
STAT uptime 2398
STAT time 1359132000
STAT version 1.4.13
STAT libevent 2.0.16-stable
STAT pointer_size 32
STAT rusage_user 0.004000
STAT rusage_system 0.128008
STAT curr_connections 7
STAT total_connections 9
STAT connection_structures 8
STAT reserved_fds 20
STAT cmd_get 1
STAT cmd_set 2
STAT cmd_flush 0
STAT cmd_touch 0
STAT get_hits 0
STAT get_misses 1
STAT delete_misses 1
STAT delete_hits 0
STAT incr_misses 0
STAT incr_hits 0
STAT decr_misses 0
STAT decr_hits 0
STAT cas_misses 0
STAT cas_hits 0
STAT cas_badval 0
STAT touch_hits 0
STAT touch_misses 0
STAT auth_cmds 0
STAT auth_errors 0
STAT bytes_read 644
STAT bytes_written 2109
STAT limit_maxbytes 67108864
STAT accepting_conns 1
STAT listen_disabled_num 0
STAT threads 4
STAT conn_yields 0
STAT hash_power_level 16
STAT hash_bytes 262144
STAT hash_is_expanding 0
STAT expired_unfetched 1
STAT evicted_unfetched 0
STAT bytes 0
STAT curr_items 0
STAT total_items 2
STAT evictions 0
STAT reclaimed 1
END

我们可以停掉某个Tomcat服务，然后观察Session会话数据的复制过程，能够保证当前集群中的会话数据不丢失，另一个结点仍然能提供基于该存在Session的服务。

参考链接

• https://code.google.com/p/memcached-session-manager
• https://code.google.com/p/memcached-session-manager/wiki/SetupAndConfiguration
• http://code.google.com/p/kryo/
• http://wiki.ubuntu.org.cn/Nginx
• http://www.iteye.com/topic/676347