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cat /etc/resolv.conf

nameserver 10.233.0.3
search default.svc.cluster.local svc.cluster.local cluster.local

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[root@node4 user1]# kubectl get svc -n kube-system
NAME                   TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)         AGE
kube-dns               ClusterIP   10.233.0.3      <none>        53/UDP,53/TCP   270d
kubernetes-dashboard   ClusterIP   10.233.22.223   <none>        443/TCP         124d

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curl b

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// search 内容类似如下（不同的pod，第一个域会有所不同）
search default.svc.cluster.local svc.cluster.local cluster.local

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const (
	// DNSClusterFirstWithHostNet indicates that the pod should use cluster DNS
	// first, if it is available, then fall back on the default
	// (as determined by kubelet) DNS settings.
	DNSClusterFirstWithHostNet DNSPolicy = "ClusterFirstWithHostNet"

	// DNSClusterFirst indicates that the pod should use cluster DNS
	// first unless hostNetwork is true, if it is available, then
	// fall back on the default (as determined by kubelet) DNS settings.
	DNSClusterFirst DNSPolicy = "ClusterFirst"

	// DNSDefault indicates that the pod should use the default (as
	// determined by kubelet) DNS settings.
	DNSDefault DNSPolicy = "Default"

	// DNSNone indicates that the pod should use empty DNS settings. DNS
	// parameters such as nameservers and search paths should be defined via
	// DNSConfig.
	DNSNone DNSPolicy = "None"
)

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apiVersion: v1
kind: Pod
metadata:
   labels:
    name: cadvisor-nodexxxx
    hostip: 192.168.x.x
  name: cadvisor-nodexxxx
  namespace: monitoring
spec:
  containers:
  - args:
    - --profiling
    - --housekeeping_interval=10s
    - --storage_duration=1m0s
    image: google/cadvisor:latest
    name: cadvisor-nodexxxx
    ports:
    - containerPort: 8080
      name: http
      protocol: TCP
    resources: {}
    securityContext:
      privileged: true
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
  dnsPolicy: ClusterFirst
  nodeName: nodexxxx

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apiVersion: v1
kind: Pod
metadata:
  namespace: default
  name: dns-example
spec:
  containers:
    - name: test
      image: nginx
  dnsPolicy: "None"
  dnsConfig:
    nameservers:
      - 1.2.3.4
    searches:
      - ns1.svc.cluster-domain.example
      - my.dns.search.suffix
    options:
      - name: ndots
        value: "2"
      - name: edns0

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nameserver 1.2.3.4
search ns1.svc.cluster-domain.example my.dns.search.suffix
options ndots:2 edns0

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  Corefile: |
    .:53 {
        errors
        log
        health {
           lameduck 15s
        }
        ready
        kubernetes  in-addr.arpa ip6.arpa {
          pods verified
          fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        forward . /etc/resolv.conf {
              prefer_udp
        }
        cache 30
        loop
        reload
        loadbalance
    }

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// SetupDNSinContainerizedMounter replaces the nameserver in containerized-mounter's rootfs/etc/resolv.conf with kubelet.ClusterDNS
func (c *Configurer) SetupDNSinContainerizedMounter(mounterPath string) {
	resolvePath := filepath.Join(strings.TrimSuffix(mounterPath, "/mounter"), "rootfs", "etc", "resolv.conf")
	dnsString := ""
	for _, dns := range c.clusterDNS {
		dnsString = dnsString + fmt.Sprintf("nameserver %s\n", dns)
	}
	if c.ResolverConfig != "" {
		f, err := os.Open(c.ResolverConfig)
		if err != nil {
			klog.ErrorS(err, "Could not open resolverConf file")
		} else {
			defer f.Close()
			_, hostSearch, _, err := parseResolvConf(f)
			if err != nil {
				klog.ErrorS(err, "Error for parsing the resolv.conf file")
			} else {
				dnsString = dnsString + "search"
				for _, search := range hostSearch {
					dnsString = dnsString + fmt.Sprintf(" %s", search)
				}
				dnsString = dnsString + "\n"
			}
		}
	}
	if err := os.WriteFile(resolvePath, []byte(dnsString), 0600); err != nil {
		klog.ErrorS(err, "Could not write dns nameserver in the file", "path", resolvePath)
	}
}

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func NewMainKubelet(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
	kubeDeps *Dependencies,
	crOptions *config.ContainerRuntimeOptions,
	hostname string,
	hostnameOverridden bool,
	nodeName types.NodeName,
	nodeIPs []net.IP,
	providerID string,
	cloudProvider string,
	certDirectory string,
	rootDirectory string,
	podLogsDirectory string,
	imageCredentialProviderConfigFile string,
	imageCredentialProviderBinDir string,
	registerNode bool,
	registerWithTaints []v1.Taint,
	allowedUnsafeSysctls []string,
	experimentalMounterPath string,
	kernelMemcgNotification bool,
	experimentalNodeAllocatableIgnoreEvictionThreshold bool,
	minimumGCAge metav1.Duration,
	maxPerPodContainerCount int32,
	maxContainerCount int32,
	registerSchedulable bool,
	nodeLabels map[string]string,
	nodeStatusMaxImages int32,
	seccompDefault bool,
) (*Kubelet, error) {
    ···

    	clusterDNS := make([]net.IP, 0, len(kubeCfg.ClusterDNS))
	for _, ipEntry := range kubeCfg.ClusterDNS {
		ip := netutils.ParseIPSloppy(ipEntry)
		if ip == nil {
			klog.InfoS("Invalid clusterDNS IP", "IP", ipEntry)
		} else {
			clusterDNS = append(clusterDNS, ip)
		}
	}
    ···
}