fix: metric server serve on all ipv4 interfaces

[prezha]

fixes #10581

before: as detailed in the original issue's description

after:

I0225 03:41:17.654624 1 node.go:172] Successfully retrieved node IP: 192.168.49.3
I0225 03:41:17.654669 1 server_others.go:142] kube-proxy node IP is an IPv4 address (192.168.49.3), assume IPv4 operation
W0225 03:41:17.673421 1 server_others.go:578] Unknown proxy mode "", assuming iptables proxy
I0225 03:41:17.673524 1 server_others.go:185] Using iptables Proxier.
I0225 03:41:17.673788 1 server.go:650] Version: v1.20.2
I0225 03:41:17.674041 1 conntrack.go:52] Setting nf_conntrack_max to 524288
E0225 03:41:17.674338 1 conntrack.go:127] sysfs is not writable: {Device:sysfs Path:/sys Type:sysfs Opts:[ro nosuid nodev noexec relatime] Freq:0 Pass:0} (mount options are [ro nosuid nodev noexec relatime])
I0225 03:41:17.674408 1 conntrack.go:100] Set sysctl 'net/netfilter/nf_conntrack_tcp_timeout_established' to 86400
I0225 03:41:17.674452 1 conntrack.go:100] Set sysctl 'net/netfilter/nf_conntrack_tcp_timeout_close_wait' to 3600
I0225 03:41:17.674569 1 config.go:315] Starting service config controller
I0225 03:41:17.674580 1 shared_informer.go:240] Waiting for caches to sync for service config
I0225 03:41:17.674658 1 config.go:224] Starting endpoint slice config controller
I0225 03:41:17.674670 1 shared_informer.go:240] Waiting for caches to sync for endpoint slice config
I0225 03:41:17.774816 1 shared_informer.go:247] Caches are synced for endpoint slice config
I0225 03:41:17.774817 1 shared_informer.go:247] Caches are synced for service config

[k8s-ci-robot]

Hi @prezha. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[minikube-bot]

Can one of the admins verify this patch?

[applitect]

As commented in the bug report, I did test this reviewing the output for successful startup of the kube-proxy on minion nodes with the following manual test cases:
✅ Tested creating 4 nodes at startup
✅ Tested creating 1 node at startup
✅ Tested adding node after startup
✅ Tested deleting node then adding new node (this one acted strange but eventually came up

[medyagh]

@prezha I see a {{.AdvertiseAddress}} that been changed to 0.0.0.0 I wonder how that affects other things ...I see it is being filled here

	opts := struct {
		CertDir             string
		ServiceCIDR         string
		PodSubnet           string
		AdvertiseAddress    string
		APIServerPort       int
		KubernetesVersion   string
		EtcdDataDir         string
		EtcdExtraArgs       map[string]string
		ClusterName         string
		NodeName            string
		DNSDomain           string
		CRISocket           string
		ImageRepository     string
		ComponentOptions    []componentOptions
		FeatureArgs         map[string]bool
		NoTaintMaster       bool
		NodeIP              string
		CgroupDriver        string
		ClientCAFile        string
		StaticPodPath       string
		ControlPlaneAddress string
		KubeProxyOptions    map[string]string
	}{
		CertDir:           vmpath.GuestKubernetesCertsDir,
		ServiceCIDR:       constants.DefaultServiceCIDR,
		PodSubnet:         podCIDR,
		AdvertiseAddress:  n.IP,

I am curious what @sadlil thinks about this PR

[prezha]

@prezha I see a {{.AdvertiseAddress}} that been changed to 0.0.0.0 I wonder how that affects other things ...I see it is being filled here

	opts := struct {
		CertDir             string
		ServiceCIDR         string
		PodSubnet           string
		AdvertiseAddress    string
		APIServerPort       int
		KubernetesVersion   string
		EtcdDataDir         string
		EtcdExtraArgs       map[string]string
		ClusterName         string
		NodeName            string
		DNSDomain           string
		CRISocket           string
		ImageRepository     string
		ComponentOptions    []componentOptions
		FeatureArgs         map[string]bool
		NoTaintMaster       bool
		NodeIP              string
		CgroupDriver        string
		ClientCAFile        string
		StaticPodPath       string
		ControlPlaneAddress string
		KubeProxyOptions    map[string]string
	}{
		CertDir:           vmpath.GuestKubernetesCertsDir,
		ServiceCIDR:       constants.DefaultServiceCIDR,
		PodSubnet:         podCIDR,
		AdvertiseAddress:  n.IP,

I am curious what @sadlil thinks about this PR

@medyagh , here we are not modifying the value of AdvertiseAddress, instead, we are using a specific value of 0.0.0.0 vs taking AdvertiseAddress as a param (as it was before)?

would love to hear also @sadlil 's thoughts too

[medyagh]

/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: prezha, sadlil
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[sadlil]

I am okay with bind the metric servers in 0.0.0.0, But I am not really sure if this could potentially open any security holes. Going through the kube-proxy docs doesn't sounds like it. If that does, user have the options to configure for different interface or disable it by --extra-config=kube-proxy.metricsBindAddress=''.

[prezha]

thank you @sadlil for your review and comments!