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oracle11gr2rac中的4种IP解说

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Jun 07, 2016 pm 02:53 PM

aboutConfiguration

关于在配置oracle 11gr2 rac时的4种IP，有不少朋友对此很迷惑，本文在此解说一下。打开一个RAC节点的/etc/hosts文件 cat /etc/hosts # Public IP 192.168.1.138rac1.localdomain rac1 192.168.1.139rac2.localdomain rac2 #Private IP 172.16.10.138rac1-pr

关于在配置oracle 11gr2 rac时的4种IP，有不少朋友对此很迷惑，本文在此解说一下。

打开一个RAC节点的/etc/hosts文件

cat /etc/hosts

# Public IP

192.168.1.138rac1.localdomain rac1

192.168.1.139rac2.localdomain rac2

#Private IP

172.16.10.138rac1-priv.localdomain rac1-priv

172.16.10.139rac2-priv.localdomain rac2-priv

#Virtual IP

192.168.1.140 rac1-vip.localdomain rac1-vip

192.168.1.141 rac2-vip.localdomain rac2-vip

#SCAN IP

192.168.1.142 rac-scan.localdomain rac-scan

这个文件里设计四种IP，分别有Public IP、Private IP、Virtual IP、SCAN IP

private ip:即内部IP。用于节点间的通信，通信内容包括network heartbeat和cache fusion
public ip:即外部IP。用于提供对外数据服务。
Virtual IP:即虚拟IP。其最大作用是用于故障切换。

Oracle RAC中每个节点都有一个虚拟IP，简称VIP，与公网PUBLIC IP在同一个网段。vip 附属在public网口接口。
Virtual IP和PUBLIC IP最主要的不同之处在于：VIP是浮动的，而PUBLIC IP是固定的。在所有节点都正常运行时，每个节点的VIP会被分配到public NIC上；在linux下ifconfig查看，public网卡上是2个IP地址；如果一个节点宕机，这个节点的VIP会被转移到还在运行的节点上。也就是幸存的节点的public NIC这个网卡上，会有3个IP地址。

如果没有vip，连接失败节点的process会有一个比较长的tcp超时等待，才能返回错误，有了vip后，节点失效后，由于vip漂移到其它节点，连接该vip的process很快就能返回错误，从而更快的尝试连接其它活动的节点，避免客户端反复连接node1的实例。如果应用程序和客户机都配置了透明的应用程序故障转移选项，可以在客户端重新连接到剩余的实例。

使用Virtual ip的另一个原因，我认为是负载均衡。客户端在配置tnsnames.ora时，有些场合是要使用的vip，而有些场合又必须使用Public IP。例如，当你在定位一个数据库的死锁时，使用Public IP，可以确保连到你想处理的机器。相反此时使用VIP时，会出现不确定性，因为服务器默认是开启负载均衡的，也就是有可能你想连A机，系统却给你分配了B机。

SCAN IP：在oracle 11gR2中，SCAN IP是作为一个新增IP出现的, scan ip其实是oracle在客户端与数据库之间，新加的一个连接层，当有客户端访问时，连接到 SCAN IP LISTENER，而SCAN IP LISTENER接收到连接请求时，会根据 LBA 算法将该客户端的连接请求，转发给对应的instance上的VIP LISTENER，从而完成了整个客户端与服务器的连接过程。简化如下：
client -> scan listener -> local listener -> local instance
你也可以把scan理解为一个虚拟主机名，它对应的是整个RAC集群。客户端主机只需通过这个scan name即可访问数据库集群的任意节点。当然访问的节点是随机的，oracle强烈建议通过DNS Server的round robin模式配置解析SCAN，实现负载均衡（即轮换连接SCAN对应的IP地址）。这有点类似通过vip和listener loadbalance配置实现负载均衡的原理。

那么有了Virtual ip后为什么还增加了一个SCAN IP呢？

在oracle 11.2之前，client链接数据库的时候要用vip，假如你的oracle cluster有4个节点，那么客户端的tnsnames.ora中就对应有四个主机vip的一个连接串，如果cluster增加了一个节点，那么对于每个连接数据库的客户端都需要修改这个tnsnames.ora。

引入了scan以后，就方便了客户端连接的一个接口，顾名思义 single client access name ，简单客户端连接名，这是一个唯一的名称，在整个公司网络内部唯一，并且在DNS中可以解析为三个ip地址，客户端连接的时候只需要知道这个名称，并连接即可，每个SCAN VIP对应一个scan listener，cluster内部的service在每个scan listener上都有注册，scan listener接受客户端的请求，并foward到不同的Local listener中去，还是由local 的listener提供服务给客户端。

scan ip主要是为了简化客户端连接，假如你的oracle 集群有20个节点，客户端连接的时候，是不是需要配置20个vip，如果用scan，只需要一个scan name就行了，剩下的事情，scan帮你做了。

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