kubeadm: check required number of CPUs on master

Implemented preflight check to ensure that number of CPUs
on the master node is not less than required.

cmd/kubeadm/app/constants/constants.go

@@ -323,6 +323,9 @@ const (
 
 	// DefaultAPIServerBindAddress is the default bind address for the API Server
 	DefaultAPIServerBindAddress = "0.0.0.0"
+
+	// MasterNumCPU is the number of CPUs required on master
+	MasterNumCPU = 2
 )
 
 var (

cmd/kubeadm/app/preflight/checks.go

@@ -845,6 +845,25 @@ func (ipc ImagePullCheck) Check() (warnings, errors []error) {
 	return warnings, errors
 }
 
+// NumCPUCheck checks if current number of CPUs is not less than required
+type NumCPUCheck struct {
+	NumCPU int
+}
+
+// Name returns the label for NumCPUCheck
+func (NumCPUCheck) Name() string {
+	return "NumCPU"
+}
+
+// Check number of CPUs required by kubeadm
+func (ncc NumCPUCheck) Check() (warnings, errors []error) {
+	numCPU := runtime.NumCPU()
+	if numCPU < ncc.NumCPU {
+		errors = append(errors, fmt.Errorf("the number of available CPUs %d is less than the required %d", numCPU, ncc.NumCPU))
+	}
+	return warnings, errors
+}
+
 // RunInitMasterChecks executes all individual, applicable to Master node checks.
 func RunInitMasterChecks(execer utilsexec.Interface, cfg *kubeadmapi.InitConfiguration, ignorePreflightErrors sets.String) error {
 	// First, check if we're root separately from the other preflight checks and fail fast
@@ -854,6 +873,7 @@ func RunInitMasterChecks(execer utilsexec.Interface, cfg *kubeadmapi.InitConfigu
 
 	manifestsDir := filepath.Join(kubeadmconstants.KubernetesDir, kubeadmconstants.ManifestsSubDirName)
 	checks := []Checker{
+		NumCPUCheck{NumCPU: kubeadmconstants.MasterNumCPU},
 		KubernetesVersionCheck{KubernetesVersion: cfg.KubernetesVersion, KubeadmVersion: kubeadmversion.Get().GitVersion},
 		FirewalldCheck{ports: []int{int(cfg.APIEndpoint.BindPort), 10250}},
 		PortOpenCheck{port: int(cfg.APIEndpoint.BindPort)},

cmd/kubeadm/app/preflight/checks_test.go

@@ -777,3 +777,24 @@ func TestImagePullCheck(t *testing.T) {
 		t.Fatalf("expected 2 errors but got %d: %q", len(errors), errors)
 	}
 }
+
+func TestNumCPUCheck(t *testing.T) {
+	var tests = []struct {
+		numCPU      int
+		numErrors   int
+		numWarnings int
+	}{
+		{0, 0, 0},
+		{999999999, 1, 0},
+	}
+
+	for _, rt := range tests {
+		warnings, errors := NumCPUCheck{NumCPU: rt.numCPU}.Check()
+		if len(warnings) != rt.numWarnings {
+			t.Errorf("expected %d warning(s) but got %d: %q", rt.numWarnings, len(warnings), warnings)
+		}
+		if len(errors) != rt.numErrors {
+			t.Errorf("expected %d warning(s) but got %d: %q", rt.numErrors, len(errors), errors)
+		}
+	}
+}