kubeadm: conditionally set the kubelet cgroup driver for Docker

Add a new utility file - util/cgroupdriver.go.
Currently it only contains the public function GetCgroupDriverDocker().
The function uses 'docker info' to obtain the cgroup driver
for Docker.

On a later stage this file can contain more methods for different
CRI.

Use GetCgroupDriverDocker() in phases/kubelet/flags.go
to conditionally set the 'cgroup-driver' argument. On error
print a warning and don't set the argument value.

Add unit tests in cgroupdriver_test.go.

cmd/kubeadm/app/phases/kubelet/BUILD

@@ -20,12 +20,14 @@ go_library(
         "//pkg/kubelet/apis/kubeletconfig/scheme:go_default_library",
         "//pkg/kubelet/apis/kubeletconfig/v1beta1: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",
         "//vendor/k8s.io/api/rbac/v1:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/types:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/wait:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes:go_default_library",
+        "//vendor/k8s.io/utils/exec:go_default_library",
     ],
 )
 

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

@@ -23,10 +23,12 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/golang/glog"
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
 	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"
+	utilsexec "k8s.io/utils/exec"
 )
 
 // WriteKubeletDynamicEnvFile writes a environment file with dynamic flags to the kubelet.
@@ -49,6 +51,13 @@ func buildKubeletArgMap(nodeRegOpts *kubeadmapi.NodeRegistrationOptions, registe
 		kubeletFlags["network-plugin"] = "cni"
 		kubeletFlags["cni-conf-dir"] = "/etc/cni/net.d"
 		kubeletFlags["cni-bin-dir"] = "/opt/cni/bin"
+		execer := utilsexec.New()
+		driver, err := kubeadmutil.GetCgroupDriverDocker(execer)
+		if err != nil {
+			glog.Warningf("cannot automatically assign a '--cgroup-driver' value when starting the Kubelet: %v\n", err)
+		} else {
+			kubeletFlags["cgroup-driver"] = driver
+		}
 	} else {
 		kubeletFlags["container-runtime"] = "remote"
 		kubeletFlags["container-runtime-endpoint"] = nodeRegOpts.CRISocket
@@ -65,7 +74,7 @@ func buildKubeletArgMap(nodeRegOpts *kubeadmapi.NodeRegistrationOptions, registe
 
 	// 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`
+	// TODO: Conditionally set `--cgroup-driver` to either `systemd` or `cgroupfs` for CRI other than Docker
 
 	return kubeletFlags
 }

cmd/kubeadm/app/util/BUILD

@@ -10,6 +10,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "arguments.go",
+        "cgroupdriver.go",
         "copy.go",
         "endpoint.go",
         "error.go",
@@ -29,6 +30,7 @@ go_library(
         "//vendor/k8s.io/apimachinery/pkg/util/net:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/validation:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes/scheme:go_default_library",
+        "//vendor/k8s.io/utils/exec:go_default_library",
     ],
 )
 
@@ -36,6 +38,7 @@ go_test(
     name = "go_default_test",
     srcs = [
         "arguments_test.go",
+        "cgroupdriver_test.go",
         "endpoint_test.go",
         "error_test.go",
         "marshal_test.go",

cmd/kubeadm/app/util/cgroupdriver.go

@@ -0,0 +1,75 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"fmt"
+	"strings"
+
+	utilsexec "k8s.io/utils/exec"
+)
+
+// TODO: add support for detecting the cgroup driver for CRI other than
+// Docker. Currently only Docker driver detection is supported:
+// Discussion:
+//     https://github.com/kubernetes/kubeadm/issues/844
+
+// GetCgroupDriverDocker runs 'docker info' to obtain the docker cgroup driver
+func GetCgroupDriverDocker(execer utilsexec.Interface) (string, error) {
+	info, err := callDockerInfo(execer)
+	if err != nil {
+		return "", err
+	}
+	return getCgroupDriverFromDockerInfo(info)
+}
+
+func validateCgroupDriver(driver string) error {
+	if driver != "cgroupfs" && driver != "systemd" {
+		return fmt.Errorf("unknown cgroup driver %q", driver)
+	}
+	return nil
+}
+
+// TODO: Docker 1.13 has a new way to obatain the cgroup driver:
+//     docker info -f "{{.CgroupDriver}}
+// If the minimum supported Docker version in K8s becomes 1.13, move to
+// this syntax.
+func callDockerInfo(execer utilsexec.Interface) (string, error) {
+	out, err := execer.Command("docker", "info").Output()
+	if err != nil {
+		return "", fmt.Errorf("cannot execute 'docker info': %v", err)
+	}
+	return string(out), nil
+}
+
+func getCgroupDriverFromDockerInfo(info string) (string, error) {
+	lineSeparator := ": "
+	prefix := "Cgroup Driver"
+	for _, line := range strings.Split(info, "\n") {
+		if !strings.Contains(line, prefix+lineSeparator) {
+			continue
+		}
+		lineSplit := strings.Split(line, lineSeparator)
+		// At this point len(lineSplit) is always >= 2
+		driver := lineSplit[1]
+		if err := validateCgroupDriver(driver); err != nil {
+			return "", err
+		}
+		return driver, nil
+	}
+	return "", fmt.Errorf("cgroup driver is not defined in 'docker info'")
+}

cmd/kubeadm/app/util/cgroupdriver_test.go

@@ -0,0 +1,68 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"testing"
+)
+
+func TestGetCgroupDriverDocker(t *testing.T) {
+	testCases := []struct {
+		name          string
+		info          string
+		expectedError bool
+	}{
+		{
+			name:          "valid: value is 'cgroupfs'",
+			info:          `Cgroup Driver: cgroupfs`,
+			expectedError: false,
+		},
+		{
+			name:          "valid: value is 'systemd'",
+			info:          `Cgroup Driver: systemd`,
+			expectedError: false,
+		},
+		{
+			name:          "invalid: missing 'Cgroup Driver' key and value",
+			info:          "",
+			expectedError: true,
+		},
+		{
+			name:          "invalid: only a 'Cgroup Driver' key is present",
+			info:          `Cgroup Driver`,
+			expectedError: true,
+		},
+		{
+			name:          "invalid: empty 'Cgroup Driver' value",
+			info:          `Cgroup Driver: `,
+			expectedError: true,
+		},
+		{
+			name:          "invalid: unknown 'Cgroup Driver' value",
+			info:          `Cgroup Driver: invalid-value`,
+			expectedError: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if _, err := getCgroupDriverFromDockerInfo(tc.info); (err != nil) != tc.expectedError {
+				t.Fatalf("expected error: %v, saw: %v, error: %v", tc.expectedError, (err != nil), err)
+			}
+		})
+	}
+}