使用hostalias为容器额外定义dns

准备个容器

apiVersion: apps/v1
kind: Deployment
metadata: 
  name: busybox
  labels: 
    app: busybox
spec: 
  replicas: 1
  selector: 
    matchLabels: 
      app: busybox
  template:
    metadata:
      labels:
        app: busybox
    spec:
      containers:
        - name: busybox
          image: centos:latest
          ports:
          - name: http
            containerPort: 8080
            protocol: TCP
          command: ["/bin/sh"]
          args: ["-c","sleep 1000"]

让我们看看他默认状态下访问百度是什么样的

[root@master ~]# kubectl exec -it busybox-54b6dd484b-9pc22 -c busybox -- sh
sh-4.4# ping baidu.com
PING baidu.com (39.156.66.10) 56(84) bytes of data.
64 bytes from 39.156.66.10 (39.156.66.10): icmp_seq=1 ttl=51 time=9.05 ms
64 bytes from 39.156.66.10 (39.156.66.10): icmp_seq=2 ttl=51 time=9.05 ms

好，让我们nslookup一下阿里云的ip，挑选其中一个

nslookup aliyun.com
Server:         100.100.2.136
Address:        100.100.2.136#53

Non-authoritative answer:
Name:   aliyun.com
Address: 106.11.249.99

加上一点小小的魔法

apiVersion: apps/v1
kind: Deployment
metadata: 
  name: busybox
  labels: 
    app: busybox
spec: 
  replicas: 1
  selector: 
    matchLabels: 
      app: busybox
  template:
    metadata:
      labels:
        app: busybox
    spec:
      hostAliases: 
      - ip: "106.11.249.99"
        hostnames: 
        -  "baidu.com"
      containers:
        - name: busybox
          image: centos:latest
          ports:
          - name: http
            containerPort: 8080
            protocol: TCP
          command: ["/bin/sh"]
          args: ["-c","sleep 1000"]

再进去看看，乐

[root@master ~]# kubectl exec -it busybox-7995d79d96-pnm2f -c busybox -- sh
sh-4.4# ping baidu.com
PING baidu.com (106.11.249.99) 56(84) bytes of data.
64 bytes from baidu.com (106.11.249.99): icmp_seq=1 ttl=48 time=26.7 ms
64 bytes from baidu.com (106.11.249.99): icmp_seq=2 ttl=48 time=26.7 ms

当你想要给你的应用配置某个dns，但是又不想直接修改coredns以影响整个集群的时候，你就可以使用这个