接上一篇继续，Domain模式解决了统一管理多台jboss的问题，今天我们来学习如何利用mod_cluster来实现负载均衡、容错。
mod_cluster是jboss的一个开源集群模块(基于apache 2.2.x)，官网地址为http://mod-cluster.jboss.org/ ，下面是使用步骤：
一、从官网下载binary文件
http://mod-cluster.jboss.org/downloads/1-2-6-Final-bin 这上面有各种OS的版本，本文以windows为试验环境，应该下载http://downloads.jboss.org/mod_cluster//1.2.6.Final/windows/mod_cluster-1.2.6.Final-windows-amd64.zip 这个版本
(注：如果是linux环境，应该下载http://downloads.jboss.org/mod_cluster//1.2.6.Final/linux-x86_64/mod_cluster-1.2.6.Final-linux2-x64.tar.gz)
二、解压安装
将下载下来的文件解压到jboss master server机器上的某个目录(假定master server的IP为172.21.129.181)，比如C:Apache2.2 ，mod_cluster其实就是一个包含集群模块的apache server，如果你的机器上之前有安装过apache server，且自动安装成了windows服务，强烈建议先卸载，否则启动mod_cluster对应的apache时，有可能启动的是之前的版本。
注：如果是linux环境安装，强烈建议将压缩包中的httpd目录，解压到/opt/jboss/目录下，因为linux版本的很多脚本和配置里，都是写死这个目录，如果修改了目录，apachectl、http.conf这些文件里的路径全都要改,十分麻烦
2.1 先执行C:Apache2.2ininstallconf.bat 生成默认配置 (注：linux环境下安装时，无需执行该步骤，直接进入2.2改http.conf文件即可)
2.2 修改C:Apache2.2confhttpd.conf
a)
#Listen 12.34.56.78:80
Listen 80
40行，把原来的端口8000，改成80，这样方便直接用 http://172.21.129.181/xxx 来访问应用
b)
164行改成
ServerName 172.21.129.181:80
c)
最后的mod_cluster部分，参考下面修改
# MOD_CLUSTER_ADDS # Adjust to you hostname and subnet. <IfModule manager_module> Listen 172.21.129.181:6666 ManagerBalancerName mycluster <VirtualHost 172.21.129.181:6666> <Location /> Order deny,allow #Deny from all Allow from all </Location> KeepAliveTimeout 300 MaxKeepAliveRequests 0 #ServerAdvertise on http://127.0.0.1:6666 AdvertiseFrequency 5 #AdvertiseSecurityKey secret #AdvertiseGroup 224.0.1.105:23364 EnableMCPMReceive <Location /mod_cluster_manager> SetHandler mod_cluster-manager Order deny,allow #Deny from all Allow from all </Location> </VirtualHost> </IfModule>
主要是把127.0.0.1，改成master server对应的真实IP，另外把Deny from all注释掉，把紧贴着的一行改成Allow from all，去掉这些访问上的限制
下面是完整的http.conf参考内容:
1 ServerRoot "C:/Apache2.2" 2 Listen 80 3 LoadModule actions_module modules/mod_actions.so 4 LoadModule alias_module modules/mod_alias.so 5 LoadModule auth_basic_module modules/mod_auth_basic.so 6 LoadModule authz_host_module modules/mod_authz_host.so 7 LoadModule autoindex_module modules/mod_autoindex.so 8 LoadModule dir_module modules/mod_dir.so 9 LoadModule log_config_module modules/mod_log_config.so 10 LoadModule mime_module modules/mod_mime.so 11 12 ServerAdmin jimmy@localhost.localdomain 13 ServerName 172.21.129.181:80 14 DocumentRoot "C:/Apache2.2/htdocs" 15 16 <Directory /> 17 Options FollowSymLinks 18 AllowOverride None 19 Order deny,allow 20 Allow from all 21 </Directory> 22 23 <Directory "C:/Apache2.2/htdocs"> 24 Options Indexes FollowSymLinks 25 AllowOverride None 26 Order allow,deny 27 Allow from all 28 </Directory> 29 30 <IfModule dir_module> 31 DirectoryIndex index.html 32 </IfModule> 33 34 <FilesMatch "^.ht"> 35 Order allow,deny 36 Deny from all 37 Satisfy All 38 </FilesMatch> 39 40 ErrorLog "logs/error_log" 41 LogLevel warn 42 <IfModule log_config_module> 43 LogFormat "%h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"" combined 44 LogFormat "%h %l %u %t "%r" %>s %b" common 45 46 <IfModule logio_module> 47 LogFormat "%h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i" %I %O" combinedio 48 </IfModule> 49 CustomLog "logs/access_log" common 50 </IfModule> 51 52 <IfModule alias_module> 53 ScriptAlias /cgi-bin/ "C:/Apache2.2/cgi-bin/" 54 </IfModule> 55 56 <Directory "C:/Apache2.2/cgi-bin"> 57 AllowOverride None 58 Options None 59 Order allow,deny 60 Allow from all 61 </Directory> 62 63 DefaultType text/plain 64 65 <IfModule mime_module> 66 TypesConfig conf/mime.types 67 AddType application/x-compress .Z 68 AddType application/x-gzip .gz .tgz 69 </IfModule> 70 71 LoadModule proxy_module modules/mod_proxy.so 72 LoadModule proxy_ajp_module modules/mod_proxy_ajp.so 73 LoadModule proxy_http_module modules/mod_proxy_http.so 74 LoadModule proxy_cluster_module modules/mod_proxy_cluster.so 75 LoadModule manager_module modules/mod_manager.so 76 LoadModule slotmem_module modules/mod_slotmem.so 77 LoadModule advertise_module modules/mod_advertise.so 78 79 # MOD_CLUSTER_ADDS 80 <IfModule manager_module> 81 Listen 172.21.129.181:6666 82 ManagerBalancerName mycluster 83 <VirtualHost 172.21.129.181:6666> 84 <Location /> 85 Order deny,allow 86 Allow from all 87 </Location> 88 KeepAliveTimeout 300 89 MaxKeepAliveRequests 0 90 AdvertiseFrequency 5 91 EnableMCPMReceive 92 <Location /mod_cluster_manager> 93 SetHandler mod_cluster-manager 94 Order deny,allow 95 Allow from all 96 </Location> 97 </VirtualHost> 98 </IfModule>
2.3 将httpd安装成windows服务
C:Apache2.2inhttpd -k install
再启动apache
C:Apache2.2inhttpd -k start
顺利的话，浏览http://172.21.129.181:6666/mod_cluster_manager 应该能看到类似以下界面：(注：不要用google chrome浏览器，chrome打不开这个地址，不知道是啥原因，换成IE或Firefox就可以了)
这是很关键的一个界面，用来管理/监控所有节点，如果没成功，请仔细检查前面的步骤是否有误。
三、以domain模式启动所有jboss master/slave server
参考上一篇的做法，启动jboss master server / slave server，完成后，刷新 http://172.21.129.181:6666/mod_cluster_manager，会看到多出了好多节点
如果没有新的节点显示在该界面，检查jboss master server中创建的group，对应的profile是否为full-ha或ha
点击相关的链接，还能看到更详细的信息
下面是点击 show INFO output后的内容：
Node: [1],Name: d2c49277-af22-32b1-95be-b70e3ff20237,Balancer: mycluster,LBGroup: ,Host: 172.21.129.128,Port: 8010,Type: ajp,Flushpackets: Off,Flushwait: 10,Ping: 10,Smax: 65,Ttl: 60,Elected: 0,Read: 0,Transfered: 0,Connected: 0,Load: 100
Node: [2],Name: 708b3ee3-fd4d-39eb-b24c-3384bd11958c,Balancer: mycluster,LBGroup: ,Host: 172.21.129.128,Port: 8009,Type: ajp,Flushpackets: Off,Flushwait: 10,Ping: 10,Smax: 65,Ttl: 60,Elected: 0,Read: 0,Transfered: 0,Connected: 0,Load: 100
Node: [3],Name: c4051fb6-9cc9-30aa-967b-6ba1294026b8,Balancer: mycluster,LBGroup: ,Host: 172.21.129.181,Port: 8011,Type: ajp,Flushpackets: Off,Flushwait: 10,Ping: 10,Smax: 65,Ttl: 60,Elected: 0,Read: 0,Transfered: 0,Connected: 0,Load: 100
Node: [4],Name: 17181717-8b5c-3289-b6ea-fedcee2a27cb,Balancer: mycluster,LBGroup: ,Host: 172.21.129.181,Port: 8012,Type: ajp,Flushpackets: Off,Flushwait: 10,Ping: 10,Smax: 65,Ttl: 60,Elected: 3,Read: 3355,Transfered: 0,Connected: 0,Load: 100
Node: [5],Name: 2465cf8d-9cb0-3248-b335-09c02f13b6fe,Balancer: mycluster,LBGroup: ,Host: 172.21.129.181,Port: 8009,Type: ajp,Flushpackets: Off,Flushwait: 10,Ping: 10,Smax: 65,Ttl: 60,Elected: 0,Read: 0,Transfered: 0,Connected: 0,Load: -1
Node: [6],Name: 68a1e90f-6645-38e0-8157-219ab2004148,Balancer: mycluster,LBGroup: ,Host: 172.21.129.181,Port: 8010,Type: ajp,Flushpackets: Off,Flushwait: 10,Ping: 10,Smax: 65,Ttl: 60,Elected: 0,Read: 0,Transfered: 0,Connected: 0,Load: -1
Node: [7],Name: b403bcec-5eb5-37a2-a956-51d273b87548,Balancer: mycluster,LBGroup: ,Host: 172.21.129.57,Port: 8011,Type: ajp,Flushpackets: Off,Flushwait: 10,Ping: 10,Smax: 65,Ttl: 60,Elected: 0,Read: 0,Transfered: 0,Connected: 0,Load: 100
Node: [8],Name: 6e5ac603-5f19-3c90-8f97-d0bf01124c94,Balancer: mycluster,LBGroup: ,Host: 172.21.129.57,Port: 8012,Type: ajp,Flushpackets: Off,Flushwait: 10,Ping: 10,Smax: 65,Ttl: 60,Elected: 0,Read: 0,Transfered: 0,Connected: 0,Load: 100
Vhost: [2:1:1], Alias: example.com
Vhost: [2:1:2], Alias: localhost
Vhost: [2:1:3], Alias: default-host
Vhost: [4:1:4], Alias: default-host
Vhost: [4:1:5], Alias: localhost
Vhost: [4:1:6], Alias: example.com
Vhost: [1:1:7], Alias: example.com
Vhost: [1:1:8], Alias: localhost
Vhost: [1:1:9], Alias: default-host
Vhost: [3:1:10], Alias: default-host
Vhost: [3:1:11], Alias: localhost
Vhost: [3:1:12], Alias: example.com
Vhost: [6:1:13], Alias: localhost
Vhost: [6:1:14], Alias: default-host
Vhost: [7:1:15], Alias: example.com
Vhost: [8:1:16], Alias: example.com
Vhost: [8:1:17], Alias: localhost
Vhost: [8:1:18], Alias: default-host
Vhost: [7:1:19], Alias: localhost
Vhost: [7:1:20], Alias: default-host
Context: [2:1:1], Context: /SSO, Status: ENABLED
Context: [4:1:2], Context: /SSO, Status: ENABLED
Context: [1:1:3], Context: /SSO, Status: ENABLED
Context: [3:1:4], Context: /SSO, Status: DISABLED
Context: [7:1:5], Context: /SSO, Status: ENABLED
Context: [8:1:6], Context: /SSO, Status: ENABLED
注意一下：虽然我们有8台jboss server，但是mod_cluster貌似最多只能支持6个node的负载均衡，有2个node的转发因子是-1，即未生效(但大多数情况下，已经够用了)。mod_cluster还有其它一些限制，详情可参考 http://docs.jboss.org/mod_cluster/1.2.0/html_single/#d0e85
四、负载均衡、容错验证
在上一篇里，已经在my-group-1、my-group-2上部署了一个名为SSO的应用，现在可以直接用 http://172.21.129.181/SSO/ 来访问了，apache会智能转发到6个节点中的某一个，如果访问正常，说明负载均衡已经生效。
继续把其它server停掉几台，再继续访问http://172.21.129.181/SSO/ ，如果仍然正常，说明某几个node损坏，并不影响正常使用，即容错成功。
所有server全shutdown后，http://172.21.129.181/SSO/ 将无法访问。
最后附一张:架构图
参考文章：