kubeadm: Set the kubelet `--resolv-conf` flag conditionally on init

cmd/kubeadm/app/phases/kubelet/BUILD

@@ -19,6 +19,7 @@ go_library(
         "//pkg/apis/rbac/v1:go_default_library",
         "//pkg/kubelet/apis/kubeletconfig/scheme:go_default_library",
         "//pkg/kubelet/apis/kubeletconfig/v1beta1:go_default_library",
+        "//pkg/util/procfs:go_default_library",
         "//pkg/util/version:go_default_library",
         "//vendor/github.com/golang/glog:go_default_library",
         "//vendor/k8s.io/api/core/v1:go_default_library",

cmd/kubeadm/app/phases/kubelet/flags.go

@@ -28,6 +28,7 @@ import (
 	kubeadmapiv1alpha2 "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1alpha2"
 	"k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
+	"k8s.io/kubernetes/pkg/util/procfs"
 	utilsexec "k8s.io/utils/exec"
 )
 
@@ -72,8 +73,12 @@ func buildKubeletArgMap(nodeRegOpts *kubeadmapi.NodeRegistrationOptions, registe
 		kubeletFlags["register-with-taints"] = strings.Join(taintStrs, ",")
 	}
 
+	if pids, _ := procfs.PidOf("systemd-resolved"); len(pids) > 0 {
+		// procfs.PidOf only returns an error if the regex is empty or doesn't compile, so we can ignore it
+		kubeletFlags["resolv-conf"] = "/run/systemd/resolve/resolv.conf"
+	}
+
 	// TODO: Pass through --hostname-override if a custom name is used?
-	// TODO: Check if `systemd-resolved` is running, and set `--resolv-conf` based on that
 	// TODO: Conditionally set `--cgroup-driver` to either `systemd` or `cgroupfs` for CRI other than Docker
 
 	return kubeletFlags

cmd/kubeadm/app/preflight/BUILD

@@ -57,7 +57,6 @@ go_library(
         "//pkg/registry/core/service/ipallocator:go_default_library",
         "//pkg/util/initsystem:go_default_library",
         "//pkg/util/ipvs:go_default_library",
-        "//pkg/util/procfs:go_default_library",
         "//pkg/util/version:go_default_library",
         "//pkg/version:go_default_library",
         "//test/e2e_node/system:go_default_library",

cmd/kubeadm/app/preflight/checks.go

@@ -51,7 +51,6 @@ import (
 	"k8s.io/kubernetes/pkg/registry/core/service/ipallocator"
 	"k8s.io/kubernetes/pkg/util/initsystem"
 	ipvsutil "k8s.io/kubernetes/pkg/util/ipvs"
-	"k8s.io/kubernetes/pkg/util/procfs"
 	versionutil "k8s.io/kubernetes/pkg/util/version"
 	kubeadmversion "k8s.io/kubernetes/pkg/version"
 	"k8s.io/kubernetes/test/e2e_node/system"
@@ -830,33 +829,6 @@ func getEtcdVersionResponse(client *http.Client, url string, target interface{})
 	return err
 }
 
-// ResolveCheck tests for potential issues related to the system resolver configuration
-type ResolveCheck struct{}
-
-// Name returns label for ResolveCheck
-func (ResolveCheck) Name() string {
-	return "Resolve"
-}
-
-// Check validates the system resolver configuration
-func (ResolveCheck) Check() (warnings, errors []error) {
-	glog.V(1).Infoln("validating the system resolver configuration")
-
-	warnings = []error{}
-
-	// procfs.PidOf only returns an error if the string passed is empty
-	// or there is an issue compiling the regex, so we can ignore it here
-	pids, _ := procfs.PidOf("systemd-resolved")
-	if len(pids) > 0 {
-		warnings = append(warnings, fmt.Errorf(
-			"systemd-resolved was detected, for cluster dns resolution to work "+
-				"properly --resolv-conf=/run/systemd/resolve/resolv.conf must be set "+
-				"for the kubelet. (/etc/systemd/system/kubelet.service.d/10-kubeadm.conf should be edited for this purpose)\n"))
-	}
-
-	return warnings, errors
-}
-
 // ImagePullCheck will pull container images used by kubeadm
 type ImagePullCheck struct {
 	Images    images.Images
@@ -1011,8 +983,7 @@ func addCommonChecks(execer utilsexec.Interface, cfg kubeadmapi.CommonConfigurat
 			InPathCheck{executable: "ethtool", mandatory: false, exec: execer},
 			InPathCheck{executable: "socat", mandatory: false, exec: execer},
 			InPathCheck{executable: "tc", mandatory: false, exec: execer},
-			InPathCheck{executable: "touch", mandatory: false, exec: execer},
-			ResolveCheck{})
+			InPathCheck{executable: "touch", mandatory: false, exec: execer})
 	}
 	checks = append(checks,
 		SystemVerificationCheck{CRISocket: cfg.GetCRISocket()},