Consul提供了两个查询接口：HTTP和DNS。DNS接口允许应用程序在没有与consul高度集成的情况下使用服务发现。 以下面这个小Consul集群为例：
root@consul:/# /usr/bin/consul members
Node Address Status Type Build Protocol DC
configuration 172.17.0.7:8301 alive client X.Y.Z 2 dc1
consul 172.17.0.2:8301 alive server X.Y.Z 2 dc1
httpd 172.17.0.4:8301 alive client X.Y.Z 2 dc1
logon 172.17.0.8:8301 alive client X.Y.Z 2 dc1
postgres 172.17.0.3:8301 alive client X.Y.Z 2 dc1
rabbitmq 172.17.0.6:8301 alive client X.Y.Z 2 dc1
可以通过DNS接口以<dnode>.node[.datacenter].<domain>的形式查询节点地址，也可以[tag.]<dservice>.service[.datacenter].<domain>的形式查询服务地址。
root@httpd:/# dig @127.0.0.1 -p53 postgres.node.consul ANY
; <<>> DiG 9.9.5-9-Debian <<>> @127.0.0.1 -p53 postgres.node.consul ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57064
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;postgres.node.consul. IN ANY
;; ANSWER SECTION:
postgres.node.consul. 0 IN A 172.17.0.3
;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Wed Jun 20 03:00:29 UTC 2018
;; MSG SIZE rcvd: 65
root@httpd:/# dig @127.0.0.1 -p53 rabbitmq.service.consul SRV
; <<>> DiG 9.9.5-9-Debian <<>> @127.0.0.1 rabbitmq.service.consul SRV
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45919
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 2
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;rabbitmq.service.consul. IN SRV
;; ANSWER SECTION:
rabbitmq.service.consul. 0 IN SRV 1 1 5672 rabbitmq.node.dc1.consul.
;; ADDITIONAL SECTION:
rabbitmq.node.dc1.consul. 0 IN A 172.17.0.6
;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Wed Jun 20 05:03:19 UTC 2018
;; MSG SIZE rcvd: 112
root@httpd:/# exit
exit
vagrant$ dig @172.17.0.2 -p53 httpd.node.consul ANY
; <<>> DiG 9.9.5-3ubuntu0.8-Ubuntu <<>> @172.17.0.2 -p53 httpd.node.consul ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48389
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;httpd.node.consul. IN ANY
;; ANSWER SECTION:
httpd.node.consul. 0 IN A 172.17.0.4
;; Query time: 0 msec
;; SERVER: 172.17.0.2#53(172.17.0.2)
;; WHEN: Wed Jun 20 03:04:15 UTC 2018
;; MSG SIZE rcvd: 68
Consul的DNS接口默认端口为8600，这里已通过Consul配置改为53。
{
"data_dir": "/opt/XXX/config/srv/consul",
"ports": {
"dns": 53
},
"leave_on_terminate": true
}
默认情况下，Consul仅对.consul域提供DNS查询服务，不支持进一步的DNS递归。可以增加上游DNS服务器已进行非Consul查询：
{
"data_dir": "/opt/XXX/config/srv/consul",
"ports": {
"dns": 53
},
"recursors": ["AAA.BBB.CCC.DDD"],
"leave_on_terminate": true
}
测试结果：
vagrant$ dig @172.17.0.2 -p53 www.sina.com.cn ANY
; <<>> DiG 9.9.5-3ubuntu0.8-Ubuntu <<>> @172.17.0.2 -p53 www.sina.com.cn ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 25127
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 27
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.sina.com.cn. IN ANY
;; ANSWER SECTION:
www.sina.com.cn. 2270 IN CNAME spool.grid.sinaedge.com.
;; AUTHORITY SECTION:
. 109385 IN NS i.root-servers.net.
. 109385 IN NS k.root-servers.net.
. 109385 IN NS c.root-servers.net.
. 109385 IN NS m.root-servers.net.
. 109385 IN NS l.root-servers.net.
. 109385 IN NS d.root-servers.net.
. 109385 IN NS g.root-servers.net.
. 109385 IN NS a.root-servers.net.
. 109385 IN NS b.root-servers.net.
. 109385 IN NS j.root-servers.net.
. 109385 IN NS h.root-servers.net.
. 109385 IN NS e.root-servers.net.
. 109385 IN NS f.root-servers.net.
;; ADDITIONAL SECTION:
a.root-servers.net. 395644 IN A 198.41.0.4
b.root-servers.net. 395644 IN A 199.9.14.201
c.root-servers.net. 395644 IN A 192.33.4.12
d.root-servers.net. 395644 IN A 199.7.91.13
e.root-servers.net. 395644 IN A 192.203.230.10
f.root-servers.net. 395644 IN A 192.5.5.241
g.root-servers.net. 395644 IN A 192.112.36.4
h.root-servers.net. 395644 IN A 198.97.190.53
i.root-servers.net. 395644 IN A 192.36.148.17
j.root-servers.net. 395644 IN A 192.58.128.30
k.root-servers.net. 395644 IN A 193.0.14.129
l.root-servers.net. 395644 IN A 199.7.83.42
m.root-servers.net. 395644 IN A 202.12.27.33
a.root-servers.net. 395644 IN AAAA 2001:503:ba3e::2:30
b.root-servers.net. 395644 IN AAAA 2001:500:200::b
c.root-servers.net. 395644 IN AAAA 2001:500:2::c
d.root-servers.net. 395644 IN AAAA 2001:500:2d::d
e.root-servers.net. 395644 IN AAAA 2001:500:a8::e
f.root-servers.net. 395644 IN AAAA 2001:500:2f::f
g.root-servers.net. 395644 IN AAAA 2001:500:12::d0d
h.root-servers.net. 395644 IN AAAA 2001:500:1::53
i.root-servers.net. 395644 IN AAAA 2001:7fe::53
j.root-servers.net. 395644 IN AAAA 2001:503:c27::2:30
k.root-servers.net. 395644 IN AAAA 2001:7fd::1
l.root-servers.net. 395644 IN AAAA 2001:500:9f::42
m.root-servers.net. 395644 IN AAAA 2001:dc3::35
;; Query time: 259 msec
;; SERVER: 172.17.0.2#53(172.17.0.2)
;; WHEN: Wed Jun 20 04:58:55 UTC 2018
;; MSG SIZE rcvd: 1539
参考
Consul DNS Interface
Consul Configuration
【Consul】Consul实践指导-DNS接口