1. 环境变量

创建pod资源时，kubectl会将其所属名称空间内的每个活动的service对象以一系列环境变量的形式注入其中。

但是也仅仅只是注入创建时候的资源，后面的变化它时不感知的。

我有个game服务：

qiteck@server:~$ sudo kubectl get service | grep game
game            NodePort    10.96.122.100   <none>        9300:9300/TCP                                                                                                                                          45h

进入另外一个k8s网络内的pod：

export | grep GAME

 qiteck@server:~$ sudo kubectl exec -it gateway-8df8488d5-tgdq6 -- /bin/bash
root@gateway-8df8488d5-tgdq6:/usr/local/openresty# export | grep GAME
declare -x GAME_PORT="tcp://10.96.122.100:9300"
declare -x GAME_PORT_9300_TCP="tcp://10.96.122.100:9300"
declare -x GAME_PORT_9300_TCP_ADDR="10.96.122.100"
declare -x GAME_PORT_9300_TCP_PORT="9300"
declare -x GAME_PORT_9300_TCP_PROTO="tcp"
declare -x GAME_SERVICE_HOST="10.96.122.100"
declare -x GAME_SERVICE_PORT="9300"
declare -x GAME_SERVICE_PORT_PORT="9300"

kubernets为每个service资源生成包括以下形式的环境变量在哪的一系列环境变量，在同一名称空间内创建的pod对象都会自动拥有这些变量: {SERVICE_NAME}_SERVICE_HOST, {SERVICE_NAME}_SERVICE_PORT

2. coredns

该主键详情见之前文章 <<kubernetes CoreDNS服务发现组件研究>>

dig srv game.default.svc.cluster.local

 root@advertise-56d599d999-c7td4:/var/app/mage-advertise# dig srv game.default.svc.cluster.local

; <<>> DiG 9.16.37-Debian <<>> srv game.default.svc.cluster.local
;; global options: +cmd
;; Got answer:
;; WARNING: .local is reserved for Multicast DNS
;; You are currently testing what happens when an mDNS query is leaked to DNS
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62959
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 2
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 996ee0ab446f6520 (echoed)
;; QUESTION SECTION:
;game.default.svc.cluster.local.	IN	SRV

;; ANSWER SECTION:
game.default.svc.cluster.local.	30 IN	SRV	0 100 9300 game.default.svc.cluster.local.

;; ADDITIONAL SECTION:
game.default.svc.cluster.local.	30 IN	A	10.96.122.100

;; Query time: 0 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: Wed Apr 26 15:02:50 CST 2023
;; MSG SIZE  rcvd: 197

可以看到：9300 game.default.svc.cluster.local，服务和端口都能找到

dig无法使用dns配置/etc/resolv.conf

more /etc/resolv.conf

 root@advertise-56d599d999-c7td4:/var/app/mage-advertise# more /etc/resolv.conf
search default.svc.cluster.local svc.cluster.local cluster.local qiteck.net localdomain
nameserver 10.96.0.10
options ndots:5

ping和telnet可以用上/etc/resolv.conf的search域名：

telnet game 9300

 root@advertise-56d599d999-c7td4:/var/app/mage-advertise# telnet game 9300
Trying 10.96.122.100...
Connected to game.default.svc.cluster.local.
Escape character is '^]'.
^C^Z^C
Connection closed by foreign host.

ping game

 root@advertise-56d599d999-c7td4:/var/app/mage-advertise# ping game
PING game.default.svc.cluster.local (10.96.122.100) 56(84) bytes of data.
^C
--- game.default.svc.cluster.local ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms

ping/telnet会根据/etc/resolv.conf的search补齐搜索的域名