kubernetes中coredns組件的高級用法

通過coredns實現內外流量分離

場景

1. 舊業務固定了域名，無法通過內部service直接訪問服務
2. 需要實現內部流量和外部流量自動拆分

實現

1. 通過coredns的rewrite功能實現以上能力,如以下內部訪問tenant.msa.chinamcloud.com域名時，會將流量轉發到tenantapi.yunjiao.svc.cluster.local域名，實現內外域名訪問一致。
2. 部分版本nginx配置時候可能遇見無法訪問的情況

[root@k8s-master1 ingress]# cat coredns.yaml
apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        rewrite name tenant.msa.chinamcloud.com tenantapi.yunjiao.svc.cluster.local
        rewrite name console.msa.chinamcloud.com console.yunjiao.svc.cluster.local
        rewrite name user.msa.chinamcloud.com userapi.yunjiao.svc.cluster.local
        rewrite name lims.msa.chinamcloud.com lims.yunjiao.svc.cluster.local
        rewrite name labapp.msa.chinamcloud.com limsapp.yunjiao.svc.cluster.local
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           upstream
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        forward . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }
kind: ConfigMap
metadata:
  creationTimestamp: "2019-04-02T04:57:19Z"
  name: coredns
  namespace: kube-system
  resourceVersion: "197"
  selfLink: /api/v1/namespaces/kube-system/configmaps/coredns
  uid: cb686453-5503-11e9-8ea6-005056be93f5

檢查

[root@k8s-master1 ingress]#  kubectl run -it --rm --restart=Never --image=infoblox/dnstools:latest dnstools
If you don't see a command prompt, try pressing enter.
dnstools# ping tenant.msa.chinamcloud.com
PING tenant.msa.chinamcloud.com (10.98.220.54): 56 data bytes
^C
--- tenant.msa.chinamcloud.com ping statistics ---
4 packets transmitted, 0 packets received, 100% packet loss

kubernetes內部實現hosts功能

coredns配置參考文檔

場景

1. 通過kubernetes的coredns實現子域名解析
2. 實現kubernetes內部 hosts綁定功能

實現

創建pod時聲明hosts(不推薦)

[root@k8s-master-1 coredns]# kubectl  explain  pods.spec.hostAliases
KIND:     Pod
VERSION:  v1

RESOURCE: hostAliases <[]Object>

DESCRIPTION:
     HostAliases is an optional list of hosts and IPs that will be injected into
     the pod's hosts file if specified. This is only valid for non-hostNetwork
     pods.

     HostAlias holds the mapping between IP and hostnames that will be injected
     as an entry in the pod's hosts file.

FIELDS:
   hostnames    <[]string>
     Hostnames for the above IP address.

   ip   <string>
     IP address of the host file entry.

[root@k8s-master-1 coredns]#

coredns的hosts特性聲明

hosts 字段部分指明瞭三個域名的解析地址

[root@k8s-master-1 coredns]# cat coredns-cm.yaml
apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        hosts {
            100.64.139.66 minio.chinamcloud.com
            100.64.139.66 registry.chinamcloud.com
            100.64.139.66 gitlab.chinamcloud.com
            fallthrough
        }
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           upstream
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        forward . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system

根據域名指定上游dns服務器

sobeydemo.com 字段指明瞭解析該域名的dns服務器地址

[root@k8s-master-1 coredns]# cat coredns-cm.yaml
apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           upstream
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        forward . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }
    sobeydemo.com {
        forward . 100.64.134.250:53
    }
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system

檢查

[root@k8s-master-1 coredns]#  kubectl run -it --rm --restart=Never --image=infoblox/dnstools:latest dnstools
If you don't see a command prompt, try pressing enter.
dnstools# host 0DJ01YUR.sobeydemo.com
0DJ01YUR.sobeydemo.com has address 100.64.148.116
0DJ01YUR.sobeydemo.com has IPv6 address 2002:6440:9474::6440:9474
dnstools# host minio.chinamcloud.com
minio.chinamcloud.com has address 100.64.139.66
Host minio.chinamcloud.com not found: 3(NXDOMAIN)
Host minio.chinamcloud.com not found: 3(NXDOMAIN)
dnstools#