一、session一致性问题
使用集群方案解决网站高并发问题时，就会部署多台应用服务器。当用户第一次通过客户端（如：浏览器）访问服务器时，服务器会创建对应的session，
使用Nginx反向代理，假如用户A第一次访问站点，被反向代理到服务器一处理，服务器一创建对应sessionA记录信息，用户A再次访问站点时，被反向代理到服务二处理，
而服务器二没有记录用户A的session信息，就会新创建sessionB，导致用户A之前操作丢失。
我们可以通过让多个服务器统一到同一个地方新建session和取session，来解决session不一致的问题。
二、基于上篇搭建好Nginx+Tomcat环境信息，可以使用memcached解决session一致性问题
三、memcached简介
Memcached是一个自由开源的，高性能，分布式内存对象缓存系统。
四、配置
1、安装Memcached，默认端口为11211，并测试
# 安装memcached，默认端口为11211
yum -y install memcached
# 启动memcached服务
# 老版本启动memcached服务
service memcached start
# 新版本启动memcached服务
systemctl start memcached.service
# 可以使用telnet测试
# 安装telnet
yum -y install telnet
# 测试
telnet 127.0.0.1 11211
2、上传jar包到tomcat的lib目录下，实现让多个服务器统一到Memcached新建session和取session
jar包可以去github查看下载，地址：https://github.com/magro/memcached-session-manager/wiki/SetupAndConfiguration
3、修改每一个tomcat配置信息
a、为了便于测试，修改/usr/local/tomcat/apache-tomcat-8.0.50/conf/server.xml文件，Engine节点添加jvmRoute="tomcat1"（103行左右，多个tomcat修改名字不同）
<Engine name="Catalina" defaultHost="localhost" jvmRoute="tomcat1" >
<?xml version='1.0' encoding='utf-8'?> <!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. --> <!-- Note: A "Server" is not itself a "Container", so you may not define subcomponents such as "Valves" at this level. Documentation at /docs/config/server.html --> <Server port="8005" shutdown="SHUTDOWN"> <Listener className="org.apache.catalina.startup.VersionLoggerListener" /> <!-- Security listener. Documentation at /docs/config/listeners.html <Listener className="org.apache.catalina.security.SecurityListener" /> --> <!--APR library loader. Documentation at /docs/apr.html --> <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" /> <!-- Prevent memory leaks due to use of particular java/javax APIs--> <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" /> <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" /> <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener" /> <!-- Global JNDI resources Documentation at /docs/jndi-resources-howto.html --> <GlobalNamingResources> <!-- Editable user database that can also be used by UserDatabaseRealm to authenticate users --> <Resource name="UserDatabase" auth="Container" type="org.apache.catalina.UserDatabase" description="User database that can be updated and saved" factory="org.apache.catalina.users.MemoryUserDatabaseFactory" pathname="conf/tomcat-users.xml" /> </GlobalNamingResources> <!-- A "Service" is a collection of one or more "Connectors" that share a single "Container" Note: A "Service" is not itself a "Container", so you may not define subcomponents such as "Valves" at this level. Documentation at /docs/config/service.html --> <Service name="Catalina"> <!--The connectors can use a shared executor, you can define one or more named thread pools--> <!-- <Executor name="tomcatThreadPool" namePrefix="catalina-exec-" maxThreads="150" minSpareThreads="4"/> --> <!-- A "Connector" represents an endpoint by which requests are received and responses are returned. Documentation at : Java HTTP Connector: /docs/config/http.html (blocking & non-blocking) Java AJP Connector: /docs/config/ajp.html APR (HTTP/AJP) Connector: /docs/apr.html Define a non-SSL/TLS HTTP/1.1 Connector on port 8080 --> <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> <!-- A "Connector" using the shared thread pool--> <!-- <Connector executor="tomcatThreadPool" port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> --> <!-- Define a SSL/TLS HTTP/1.1 Connector on port 8443 This connector uses the NIO implementation that requires the JSSE style configuration. When using the APR/native implementation, the OpenSSL style configuration is required as described in the APR/native documentation --> <!-- <Connector port="8443" protocol="org.apache.coyote.http11.Http11NioProtocol" maxThreads="150" SSLEnabled="true" scheme="https" secure="true" clientAuth="false" sslProtocol="TLS" /> --> <!-- Define an AJP 1.3 Connector on port 8009 --> <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" /> <!-- An Engine represents the entry point (within Catalina) that processes every request. The Engine implementation for Tomcat stand alone analyzes the HTTP headers included with the request, and passes them on to the appropriate Host (virtual host). Documentation at /docs/config/engine.html --> <!-- You should set jvmRoute to support load-balancing via AJP ie : <Engine name="Catalina" defaultHost="localhost" jvmRoute="jvm1"> --> <Engine name="Catalina" defaultHost="localhost" jvmRoute="tomcat1" > <!--For clustering, please take a look at documentation at: /docs/cluster-howto.html (simple how to) /docs/config/cluster.html (reference documentation) --> <!-- <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/> --> <!-- Use the LockOutRealm to prevent attempts to guess user passwords via a brute-force attack --> <Realm className="org.apache.catalina.realm.LockOutRealm"> <!-- This Realm uses the UserDatabase configured in the global JNDI resources under the key "UserDatabase". Any edits that are performed against this UserDatabase are immediately available for use by the Realm. --> <Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="UserDatabase"/> </Realm> <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true"> <!-- SingleSignOn valve, share authentication between web applications Documentation at: /docs/config/valve.html --> <!-- <Valve className="org.apache.catalina.authenticator.SingleSignOn" /> --> <!-- Access log processes all example. Documentation at: /docs/config/valve.html Note: The pattern used is equivalent to using pattern="common" --> <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs" prefix="localhost_access_log" suffix=".txt" pattern="%h %l %u %t "%r" %s %b" /> </Host> </Engine> </Service> </Server>
b、修改/usr/local/tomcat/apache-tomcat-8.0.50/conf/context.xml，实现tomcat到Memcached新建session和取session，在Context节点里添加如下配置，
memcachedNodes="n1:192.168.182.131:11211"，这个ip需要是自己安装的Memcached的ip
<Manager className="de.javakaffee.web.msm.MemcachedBackupSessionManager" memcachedNodes="n1:192.168.182.131:11211" requestUriIgnorePattern=".*.(ico|png|gif|jpg|css|js)$"
/>
<?xml version='1.0' encoding='utf-8'?> <!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. --> <!-- The contents of this file will be loaded for each web application --> <Context> <!-- Default set of monitored resources. If one of these changes, the --> <!-- web application will be reloaded. --> <WatchedResource>WEB-INF/web.xml</WatchedResource> <WatchedResource>${catalina.base}/conf/web.xml</WatchedResource> <!-- Uncomment this to disable session persistence across Tomcat restarts --> <!-- <Manager pathname="" /> --> <!-- Uncomment this to enable Comet connection tacking (provides events on session expiration as well as webapp lifecycle) --> <!-- <Valve className="org.apache.catalina.valves.CometConnectionManagerValve" /> --> <Manager className="de.javakaffee.web.msm.MemcachedBackupSessionManager" memcachedNodes="n1:192.168.182.131:11211" requestUriIgnorePattern=".*.(ico|png|gif|jpg|css|js)$" /> </Context>
五、测试
浏览器访问192.168.182.130，ctrl + F5刷新浏览器，查看session信息是否和预期一致。
六、tomcat和nginx安装可以参考个人的随笔
yexiangyang
moyyexy@gmail.com