RedHat6 叢集Fence
實驗目的：
掌握叢集Fence理論和配置
Fence概念:
在HA叢集壞境中，備份伺服器B通過心跳線來發送資料包來看伺服器A是否還活着，主伺服器A接收了大量的用戶端通路請求，伺服器A的CPU負載達到100%響應不過來了，資源已經耗盡，沒有辦法回複伺服器B資料包（回複資料包會延遲），這時伺服器B認為伺服器A已經挂了，于是備份伺服器B把資源奪過來，自己做主伺服器，過了一段時間伺服器A響應過來了，伺服器A覺得自己是老大，伺服器B覺得自己也是老大，他們兩個就掙着搶奪資源，叢集資源被多個節點占有，兩個伺服器同時向資源寫資料，破壞了資源的安全性和一緻性，這種情況的發生叫做“腦裂”。伺服器A負載過重，響應不過來了，有了Fence機制，Fence會自動的把伺服器A給Fence掉，阻止了“腦裂"的發生
Fence分類：
硬體Fence：電源Fence，通過關掉電源來踢掉壞的伺服器
軟體Fence：Fence卡（智能卡），通過線纜、軟體來踢掉壞的伺服器
實際壞境中，Fence卡連接配接的都是專線，使用專用的Fence網卡，不會占用資料傳輸線路，這樣，更能保證穩定及可靠性。
Fence卡的IP網絡和叢集網絡是互相依存的
實驗步驟：
由于實際情況的限制，沒有真實的Fence卡，所用我們用fence服務來虛拟出Fence卡
在iscsi伺服器上安裝fence服務，把iscsi伺服器當成fence卡
安裝fence卡，你隻需要安裝fence-virtd-libvirt.x86_64和fence-virtd-multicast.x86_64這兩個軟體就可以了
[root@node1 ~]# yum list | grep fence
Repository ResilientStorage is listed morethan once in the configuration
Repository ScalableFileSystem is listedmore than once in the configuration
fence-agents.x86_64 3.1.5-10.el6 @Cluster
fence-virt.x86_64 0.2.3-5.el6 @Cluster
fence-virtd.x86_64 0.2.3-5.el6 base
fence-virtd-checkpoint.x86_64 0.2.3-5.el6 Cluster
fence-virtd-libvirt.x86_64 0.2.3-5.el6 base
fence-virtd-libvirt-qpid.x86_64 0.2.3-5.el6 optional
fence-virtd-multicast.x86_64 0.2.3-5.el6 base
fence-virtd-serial.x86_64 0.2.3-5.el6 base
[root@node1 ~]# yum -y install fence-virtd-libvirt.x86_64 fence-virtd-multicast.x86_64
[root@desktop24 ~]# mkdir /etc/cluster
[root@desktop24 ~]# cd /etc/cluster
[root@desktop24 cluster]# dd if=/dev/random of=/etc/cluster/fence_xvm.key bs=4k count=1 建立fence卡的key檔案，讓節點伺服器和Fence卡互相認識
0+1 records in
0+1 records out
73 bytes (73 B) copied, 0.000315063 s, 232kB/s
random：為随機數字生成器，生成的東西是唯一的
fence_xvm.key:Fence卡的key檔案，名字别改，fence_xvm是fence卡的一種類型
把fence的key檔案分發給各個節點伺服器
[root@desktop24cluster]#scp/etc/cluster/fence_xvm.key 172.17.0.1:/etc/cluster/fence_xvm.key
[email protected]'s password:
fence_xvm.key 100% 73 0.1KB/s 00:00
[root@desktop24 cluster]# scp /etc/cluster/fence_xvm.key 172.17.0.2:/etc/cluster/fence_xvm.key
[email protected]'s password:
fence_xvm.key 100% 73 0.1KB/s 00:00
對fence服務的配置檔案/etc/fence_virt.conf做配置政策：
[root@desktop24 cluster]# fence_virtd -c
Module search path[/usr/lib64/fence-virt]:
//子產品搜尋路徑，回車使用預設的
Available backends:
libvirt 0.1
Available listeners:
multicast 1.1
Listener modules are responsible foraccepting requests
from fencing clients.
Listener module [multicast]:
//監聽多點傳播子產品，回車選擇預設
The multicast listener module is designedfor use environments
where the guests and hosts may communicateover a network using
multicast.
The multicast address is the address that aclient will use to
send fencing requests to fence_virtd.
Multicast IP Address[225.0.0.12]:
多點傳播IP位址選擇，回車選擇預設的225.0.0.12
Using ipv4 as family.
Multicast IP Port [1229]:
//多點傳播IP端口選擇，回車選擇預設的1229
Setting a preferred interface causes fence_virtdto listen only
on that interface. Normally, it listens on all interfaces.
In environments where the virtual machinesare using the host
machine as a gateway, this *must* be set(typically to virbr0).
Set to 'none' for no interface.
Interface [none]: private
//Fence卡使用那個接口來和叢集網絡來通訊（fence卡的專用接口和叢集網絡在同一網段）
The key file is the shared key informationwhich is used to
authenticate fencing requests. The contents of this file must
be distributed to each physical host andvirtual machine within
a cluster.
Key File[/etc/cluster/fence_xvm.key]:
//是否是對/etc/cluster/fence_xvm.key這個檔案做政策，回車選擇預設的
Backend modules are responsible for routingrequests to
the appropriate hypervisor or managementlayer.
Backend module [checkpoint]:libvirt
//子產品基于那個協定，填寫libvirt
The libvirt backend module is designed forsingle desktops or
servers. Do not use in environments where virtual machines
may be migrated between hosts.
Libvirt URI [qemu:///system]:
Configuration complete.
=== Begin Configuration ===
backends {
libvirt{
uri= "qemu:///system";
}
}
listeners {
multicast{
interface= "eth0";
port= "1229";
family= "ipv4";
address= "225.0.0.12";
key_file= "/etc/cluster/fence_xvm.key";
fence_virtd {
module_path= "/usr/lib64/fence-virt";
backend= "libvirt";
listener= "multicast";
=== End Configuration ===
Replace /etc/fence_virt.confwith the above [y/N]? y
//輸入y儲存配置
啟動fence服務：
[root@desktop24 cluster]# /etc/init.d/fence_virtd restart
Stopping fence_virtd: [FAILED]
Starting fence_virtd: [ OK ]
[root@desktop24 cluster]# chkconfig fence_virtd on
把fence卡加入到叢集：
Fence Dervices中點選add來添加fence卡（虛拟的）
打開【Select a fence device】選擇【Fence virt（Multicast Mode）】，名字寫這個Fence卡名字
虛拟的Fence裝置添加完成後，界面如下：
把Fence卡添加到各個節點中去：
添加fence卡到Node1中：
選擇【Node】，然後點選Node1節點的界面，找到下圖位置添加Fence
取名根據自己需要，隻要能識别即可
然後點選【Add Fence Instance】，添加Fence實咧
選擇Fence1這個Fence卡，這裡的domain指的的是node1.private.cluster0.example.com中的node1
添加Fence卡到Node2中：
把界面換到節點2中
找到下圖位置，點選【Add Fence Method】
給Fence Method起名字
點選【Add Fence Instance】
選擇Fence1這個Fence卡，這裡的domain指的的是node2.private.cluster0.example.com中的node2
手動fence剔除：
[root@node2 ~]# fence_node node1