Tomcat集群概要

其实已经有很多文档了，不过还是老话，给自己备忘，总结些要注意的要点，给一些范例，以后肯定用得着。

以JK作为Apache和Tomcat的连接器，首先配置的是Apache的httpd.conf，主要是加载JK和配置转发规则：
加载和配置JK：
# Load mod_jk module
# Specify the filename of the mod_jk lib
LoadModule jk_module modules/mod_jk.so

# Where to find workers.properties
JkWorkersFile workers2.properties

# Where to put jk logs
JkLogFile logs/mod_jk.log

# Set the jk log level [debug/error/info]
JkLogLevel info

# Select the log format
JkLogStampFormat  "[%a %b %d %H:%M:%S %Y]"

# JkOptions indicates to send SSK KEY SIZE
JkOptions +ForwardKeySize +ForwardURICompat -ForwardDirectories

# JkRequestLogFormat
JkRequestLogFormat "%w %V %T"

配置转发规则：
JKMount /*  loadbalancer
这个上面的配置差异比较大，简单起见全部转发，可以根据自己的需要修改

然后是定义Workers：

info=Scoreboard. Requried for reconfiguration and status with multiprocess servers.
#file=anon
file=logs/shm.file
size=1048576

# Defines a load balancer named lb. Use even if you only have one machine.
[lb:lb]

# Example socket channel, override port and host.
[channel.socket:192.168.1.16:8009]
port=8009
host=192.168.1.16

[channel.socket:192.168.1.18:8009]
port=8009
host=192.168.1.18

# Map the Tomcat examples webapp to the Web server uri space
worker.list=loadbalancer

worker.worker1.port=8009
worker.worker1.host=192.168.1.16
worker.worker1.type=ajp13
worker.worker1.lbfactor=1
worker.worker1.cachesize=60
worker.worker1.cache_timeout=300
worker.worker1.socket_keepalive=1
worker.worker1.socket_timeout=180
worker.worker1.connect_timeout=0
worker.worker1.reply_timeout=0
worker.worker1.recovery_options=1
worker.worker1.retries=1

worker.worker2.port=8009
worker.worker2.host=192.168.1.18
worker.worker2.type=ajp13
worker.worker2.lbfactor=1
worker.worker2.cachesize=60
worker.worker2.cache_timeout=300
worker.worker2.socket_keepalive=1
worker.worker2.socket_timeout=180
worker.worker2.connect_timeout=0
worker.worker2.reply_timeout=0
worker.worker2.recovery_options=1
worker.worker2.retries=1

worker.loadbalancer.type=lb
worker.loadbalancer.balance_workers=worker1,worker2
worker.loadbalancer.sticky_session=1

[uri:/*]
group=lb

[status:status]
info=Status worker, displays runtime informations
   
# Status worker for managing load balancer
# worker.status.type=status

[uri:/jkstatus/*]
info=Display status information and checks the config file for changes.
group=status:status

上面的jkstatus的配置是可选的，在开发环境中打开，但是在产品环境中最好关闭。
使用了粘性Session（worker.loadbalancer.sticky_session=1），所以Tomcat的Server.xml中的Engine元素需要添加jvmRoute属性，值就是对应的worker的名字，另外Server.xml中的cluster配置不要打开，否则会进行session的复制。
相关的文章：
http://tomcat.apache.org/connectors-doc/generic_howto/loadbalancers.html
http://tomcat.apache.org/tomcat-5.0-doc/cluster-howto.html
http://blog.csdn.net/ladofwind/archive/2006/08/29/1138484.aspx
http://tomcat.jaxmao.org/cluster-howto.html
http://www.matrix.org.cn/thread.shtml?topicId=39848&forumId=27