DNS 的负载均衡
通过 DNS 实现的负载均衡只是简单的轮询，还有就是不能对后端节点进行健康检测，了解这个特点即可，不建议使用 DNS 来做这种负载均衡。
配置 DNS 视图来实现智能 DNS
原理：根据客户端的 IP 来返回对应的资源记录
1 named.conf 增加 acl group 配置
[root@ns-master ~]# cat /var/named/chroot/etc/named.conf
options {
version "1.1.1";
listen-on port 53 {any;};
directory "/var/named/chroot/etc/";
pid-file "/var/named/chroot/var/run/named/named.pid";
allow-query { any; };
Dump-file "/var/named/chroot/var/log/binddump.db";
Statistics-file "/var/named/chroot/var/log/named_stats";
zone-statistics yes;
memstatistics-file "log/mem_stats";
empty-zones-enable no;
forwarders {202.106.196.115;8.8.8.8; };
};
key "rndc-key" {
algorithm hmac-md5;
secret "Eqw4hClGExUWeDkKBX/pBg==";
};
controls {
inet 127.0.0.1 port 953
allow { 127.0.0.1; } keys { "rndc-key"; };
};
logging {
channel warning {
file "/var/named/chroot/var/log/dns_warning" versions 10 size 10m;
severity warning;
print-category yes;
print-severity yes;
print-time yes;
};
channel general_dns {
file "/var/named/chroot/var/log/dns_log" versions 10 size 100m;
severity info;
print-category yes;
print-severity yes;
print-time yes;
};
category default {
warning;
};
category queries {
general_dns;
};
};
acl group1 {
192.168.56.13;
};
acl group2 {
192.168.56.14;
};
include "/var/named/chroot/etc/view.conf";
2 配置视图文件 view.conf 中不同的组使用不同的区域文件（同一域名下）
[root@ns-master ~]# cat /var/named/chroot/etc/view.conf
view "GROUP1" {
match-clients { group1; };
zone "viewexample.com" {
type master;
file "group1.viewexample.com.zone";
};
};
view "GROUP2" {
match-clients { group2; };
zone "viewexample.com" {
type master;
file "group2.viewexample.com.zone";
};
};
3 同一域名下不同的区域文件内容
一个域名对应多个 A 记录，分别在不同的区域文件配置
vim /var/named/chroot/etc/group1.viewexample.com.zone
$ORIGIN .
$TTL 3600 ; 1 hour
viewexample.com IN SOA op.viewexample.com. dns.viewexample.com. (
2005 ; serial
900 ; refresh (15 minutes)
600 ; retry (10 minutes)
86400 ; expire (1 day)
3600 ; minimum (1 hour)
)
NS op.viewexample.com.
$ORIGIN viewexample.com.
op A 192.168.122.1
view A 192.168.122.1
vim /var/named/chroot/etc/group2.viewexample.com.zone
$ORIGIN .
$TTL 3600 ; 1 hour
viewexample.com IN SOA op.viewexample.com. dns.viewexample.com. (
2005 ; serial
900 ; refresh (15 minutes)
600 ; retry (10 minutes)
86400 ; expire (1 day)
3600 ; minimum (1 hour)
)
NS op.viewexample.com.
$ORIGIN viewexample.com.
op A 192.168.122.2
view A 192.168.122.2
# 修改区域文件属主后重新加载
chown named.named /var/named/chroot/etc/group*.zone
rndc reload
4 分别在不同 IP 的服务器上测试同一域名返回的 A 记录
[root@ns-master ~]# ip a | grep eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
inet 192.168.56.13/24 brd 192.168.56.255 scope global eth0
[root@ns-master ~]# host view.viewexample.com 192.168.56.13
Using domain server:
Name: 192.168.56.13
Address: 192.168.56.13#53
Aliases:
view.viewexample.com has address 192.168.122.1
[root@ns-slave ~]# host view.viewexample.com 192.168.56.13
Using domain server:
Name: 192.168.56.13
Address: 192.168.56.13#53
Aliases:
view.viewexample.com has address 192.168.122.2
# 可以从上面的结果看到，在不同的服务器上，view.viewexample.com 返回的 IP 地址不同。
