5.6.4　更改集群CoreDNS配置

可以通过以下命令来获取istiocoredns服务的Cluster IP：

kubectl get svc istiocoredns -n istio-system

NAME           TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)         AGE
istiocoredns   ClusterIP   172.19.10.196   <none>        53/UDP,53/TCP   44m

更新集群的CoreDNS的配置项conf igmap，将此istiocoredns服务作为*.global域的上游DNS服务，在此配置项conf igmap中添加域*.global，如下所示：

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |-
    .:53 {
        errors
        health
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           upstream
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        proxy . /etc/resolv.conf
        cache 30
        reload
    }
    global:53 {
         errors
         cache 30
         proxy . {replace this with the actual cluster IP of this istiocoredns service}
    }

更改此配置项后，集群的CoreDNS容器会重新加载这些配置内容，可以通过如下命令查看加载日志：

kubectl get -n kube-system pod | grep coredns
coredns-8645f4b4c6-5frkg                        1/1     Running   0      20h
coredns-8645f4b4c6-lj59t                        1/1     Running   0      20h

kubectl logs -f -n kube-system coredns-8645f4b4c6-5frkg
....
2019/01/08 05:06:47 [INFO] Reloading
2019/01/08 05:06:47 [INFO] plugin/reload: Running configuration MD5 = 05514b3e44bcf4ea805c87cc6cd56c07
2019/01/08 05:06:47 [INFO] Reloading complete

kubectl logs -f -n kube-system coredns-8645f4b4c6-lj59t
....
2019/01/08 05:06:31 [INFO] Reloading
2019/01/08 05:06:32 [INFO] plugin/reload: Running configuration MD5 = 05514b3e44bcf4ea805c87cc6cd56c07
2019/01/08 05:06:32 [INFO] Reloading complete