Kubernetes DNS拓展Kubernetes DNS在内部服务与外部服务交互，内部服务与内部服务，内部服务与云托

Kubernetes DNS在内部服务与外部服务交互，内部服务与内部服务，内部服务与云托管服务交互的工具，拓展DNS可以在内部服务访问集群外服务时像访问集群内服务一样，通过DNS映射将统一风格的域名映射到可访问的IP，而不需要影响内部服务的运行。

自定义域名解析

拓展DNS的方法就是为特定规则的域名指定DNS服务器，在ConfigMap中设置指定域名相对的dns server，如consul.local结尾的域名使用10.150.0.1来解析。

apiVersion: v1
kind: ConfigMap
metadata:
  name: kube-dns
  namespace: kube-system
data:
  stubDomains: |
    {"consul.local": ["10.150.0.1"]}
  upstreamNameservers: |
    ["172.16.0.1"]

自定义规则不对dnsPolicy为Default或None的Pod起作用，只有当ClusterFirst时，域名解析会按照stubDomains和upstreamNameservers来解析。
无自定义配置: 任何不匹配集群域名后缀的请求，被转发给节点的dns.
自定义: 如果stub和upstream配置，按照如下顺序

带集群后缀的，请求转发给kube-dns
stub后缀的，转发给指定的dns
其它的转发给upstream dns

Consul as a DNS

Consul是Golang实现的服务发现工具，同时支持DNS解析，通过HTTP API动态添加服务发现节点实现动态DNS解析。

注册Redis1到redis

{
  "ID": "redis1",
  "Name": "redis",
  "Tags": [
    "primary",
    "v1"
  ],
  "Address": "127.0.0.1",
  "Port": 8000,
  "Meta": {
    "redis_version": "4.0"
  },
  "EnableTagOverride": false
}

$ curl -XPUT http://localhost:8500/v1/agent/service/register -d @dns.json

使用DNS查询

$ dig @127.0.0.1 -p 8600 redis.service.consul SRV
; <<>> DiG 9.10.6 <<>> @127.0.0.1 -p 8600 redis.service.consul SRV
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6823
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 3
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;redis.service.consul.		IN	SRV

;; ANSWER SECTION:
redis.service.consul.	0	IN	SRV	1 1 8000 srjiangs-MacBook-Pro.local.node.dc1.consul.

;; ADDITIONAL SECTION:
srjiangs-MacBook-Pro.local.node.dc1.consul. 0 IN A 127.0.0.1
srjiangs-MacBook-Pro.local.node.dc1.consul. 0 IN TXT "consul-network-segment="

注册多个Redis

{
  "ID": "redis2",
  "Name": "redis",
  "Tags": [
    "primary",
    "v1"
  ],
  "Address": "127.0.0.1",
  "Port": 8000,
  "Meta": {
    "redis_version": "4.0"
  },
  "EnableTagOverride": false
}

$ curl -XPUT http://localhost:8500/v1/agent/service/register -d @dns.json

DNS查询

$ dig @127.0.0.1 -p 8600 redis.service.consul SRV

; <<>> DiG 9.10.6 <<>> @127.0.0.1 -p 8600 redis.service.consul SRV
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11920
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 5
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;redis.service.consul.		IN	SRV

;; ANSWER SECTION:
redis.service.consul.	0	IN	SRV	1 1 9000 srjiangs-MacBook-Pro.local.node.dc1.consul.
redis.service.consul.	0	IN	SRV	1 1 8000 srjiangs-MacBook-Pro.local.node.dc1.consul.

;; ADDITIONAL SECTION:
srjiangs-MacBook-Pro.local.node.dc1.consul. 0 IN A 127.0.0.1
srjiangs-MacBook-Pro.local.node.dc1.consul. 0 IN TXT "consul-network-segment="
srjiangs-MacBook-Pro.local.node.dc1.consul. 0 IN A 127.0.0.1
srjiangs-MacBook-Pro.local.node.dc1.consul. 0 IN TXT "consul-network-segment="

;; Query time: 0 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Thu Aug 16 16:47:43 CST 2018
;; MSG SIZE  rcvd: 277

Consul Service

$ curl http://localhost:8500/v1/agent/services

{
	"redis1": {
		"ID": "redis1",
		"Service": "redis",
		"Tags": [
			"primary",
			"v1"
		],
		"Address": "127.0.0.1",
		"Port": 8000,
		"EnableTagOverride": false,
		"CreateIndex": 0,
		"ModifyIndex": 0
	},
	"redis2": {
		"ID": "redis2",
		"Service": "redis",
		"Tags": [
			"primary",
			"v1"
		],
		"Address": "127.0.0.1",
		"Port": 9000,
		"EnableTagOverride": false,
		"CreateIndex": 0,
		"ModifyIndex": 0
	}
}

引用

Customizing DNS Service - Kubernetes

GitHub - skynetservices/skydns: DNS service discovery for etcd

Adding entries to Pod /etc/hosts with HostAliases - Kubernetes

Kubernetes DNS拓展

自定义域名解析

Consul as a DNS

更多细节

引用