server.go

/*
Copyright 2015 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 app makes it easy to create a kubelet server for various contexts.
package app

import (
	"crypto/tls"
	"errors"
	"fmt"
	"math/rand"
	"net"
	"net/http"
	_ "net/http/pprof"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"time"

	"github.com/golang/glog"
	"github.com/spf13/cobra"
	"github.com/spf13/pflag"

	"k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/api/resource"
	"k8s.io/apimachinery/pkg/types"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/apimachinery/pkg/util/wait"
	"k8s.io/apiserver/pkg/server/healthz"
	utilfeature "k8s.io/apiserver/pkg/util/feature"
	"k8s.io/apiserver/pkg/util/flag"
	clientgoclientset "k8s.io/client-go/kubernetes"
	clientset "k8s.io/client-go/kubernetes"
	v1core "k8s.io/client-go/kubernetes/typed/core/v1"
	restclient "k8s.io/client-go/rest"
	"k8s.io/client-go/tools/clientcmd"
	"k8s.io/client-go/tools/record"
	certutil "k8s.io/client-go/util/cert"
	"k8s.io/kubernetes/cmd/kubelet/app/options"
	"k8s.io/kubernetes/pkg/api"
	"k8s.io/kubernetes/pkg/capabilities"
	"k8s.io/kubernetes/pkg/client/chaosclient"
	"k8s.io/kubernetes/pkg/cloudprovider"
	"k8s.io/kubernetes/pkg/credentialprovider"
	"k8s.io/kubernetes/pkg/features"
	"k8s.io/kubernetes/pkg/kubelet"
	kubeletconfiginternal "k8s.io/kubernetes/pkg/kubelet/apis/kubeletconfig"
	kubeletscheme "k8s.io/kubernetes/pkg/kubelet/apis/kubeletconfig/scheme"
	kubeletconfigv1alpha1 "k8s.io/kubernetes/pkg/kubelet/apis/kubeletconfig/v1alpha1"
	"k8s.io/kubernetes/pkg/kubelet/cadvisor"
	"k8s.io/kubernetes/pkg/kubelet/certificate"
	"k8s.io/kubernetes/pkg/kubelet/certificate/bootstrap"
	"k8s.io/kubernetes/pkg/kubelet/cm"
	"k8s.io/kubernetes/pkg/kubelet/config"
	kubecontainer "k8s.io/kubernetes/pkg/kubelet/container"
	"k8s.io/kubernetes/pkg/kubelet/dockershim"
	"k8s.io/kubernetes/pkg/kubelet/dockershim/libdocker"
	dockerremote "k8s.io/kubernetes/pkg/kubelet/dockershim/remote"
	"k8s.io/kubernetes/pkg/kubelet/eviction"
	evictionapi "k8s.io/kubernetes/pkg/kubelet/eviction/api"
	"k8s.io/kubernetes/pkg/kubelet/kubeletconfig"
	"k8s.io/kubernetes/pkg/kubelet/server"
	"k8s.io/kubernetes/pkg/kubelet/server/streaming"
	kubetypes "k8s.io/kubernetes/pkg/kubelet/types"
	"k8s.io/kubernetes/pkg/util/configz"
	"k8s.io/kubernetes/pkg/util/flock"
	kubeio "k8s.io/kubernetes/pkg/util/io"
	"k8s.io/kubernetes/pkg/util/mount"
	nodeutil "k8s.io/kubernetes/pkg/util/node"
	"k8s.io/kubernetes/pkg/util/oom"
	"k8s.io/kubernetes/pkg/util/rlimit"
	"k8s.io/kubernetes/pkg/version"
)

const (
	// Kubelet component name
	componentKubelet = "kubelet"
)

// NewKubeletCommand creates a *cobra.Command object with default parameters
func NewKubeletCommand() *cobra.Command {
	// ignore the error, as this is just for generating docs and the like
	s, _ := options.NewKubeletServer()
	s.AddFlags(pflag.CommandLine)
	cmd := &cobra.Command{
		Use: componentKubelet,
		Long: `The kubelet is the primary "node agent" that runs on each
node. The kubelet works in terms of a PodSpec. A PodSpec is a YAML or JSON object
that describes a pod. The kubelet takes a set of PodSpecs that are provided through
various mechanisms (primarily through the apiserver) and ensures that the containers
described in those PodSpecs are running and healthy. The kubelet doesn't manage
containers which were not created by Kubernetes.

Other than from an PodSpec from the apiserver, there are three ways that a container
manifest can be provided to the Kubelet.

File: Path passed as a flag on the command line. Files under this path will be monitored
periodically for updates. The monitoring period is 20s by default and is configurable
via a flag.

HTTP endpoint: HTTP endpoint passed as a parameter on the command line. This endpoint
is checked every 20 seconds (also configurable with a flag).

HTTP server: The kubelet can also listen for HTTP and respond to a simple API
(underspec'd currently) to submit a new manifest.`,
		Run: func(cmd *cobra.Command, args []string) {
		},
	}

	return cmd
}

// UnsecuredDependencies returns a Dependencies suitable for being run, or an error if the server setup
// is not valid.  It will not start any background processes, and does not include authentication/authorization
func UnsecuredDependencies(s *options.KubeletServer) (*kubelet.Dependencies, error) {
	// Initialize the TLS Options
	tlsOptions, err := InitializeTLS(&s.KubeletFlags, &s.KubeletConfiguration)
	if err != nil {
		return nil, err
	}

	mounter := mount.New(s.ExperimentalMounterPath)
	var writer kubeio.Writer = &kubeio.StdWriter{}
	if s.Containerized {
		glog.V(2).Info("Running kubelet in containerized mode (experimental)")
		mounter = mount.NewNsenterMounter()
		writer = &kubeio.NsenterWriter{}
	}

	var dockerClient libdocker.Interface
	if s.ContainerRuntime == kubetypes.DockerContainerRuntime {
		dockerClient = libdocker.ConnectToDockerOrDie(s.DockerEndpoint, s.RuntimeRequestTimeout.Duration,
			s.ImagePullProgressDeadline.Duration)
	} else {
		dockerClient = nil
	}

	return &kubelet.Dependencies{
		Auth:                nil, // default does not enforce auth[nz]
		CAdvisorInterface:   nil, // cadvisor.New launches background processes (bg http.ListenAndServe, and some bg cleaners), not set here
		Cloud:               nil, // cloud provider might start background processes
		ContainerManager:    nil,
		DockerClient:        dockerClient,
		KubeClient:          nil,
		ExternalKubeClient:  nil,
		EventClient:         nil,
		Mounter:             mounter,
		NetworkPlugins:      ProbeNetworkPlugins(s.NetworkPluginDir, s.CNIConfDir, s.CNIBinDir),
		OOMAdjuster:         oom.NewOOMAdjuster(),
		OSInterface:         kubecontainer.RealOS{},
		Writer:              writer,
		VolumePlugins:       ProbeVolumePlugins(),
		DynamicPluginProber: GetDynamicPluginProber(s.VolumePluginDir),
		TLSOptions:          tlsOptions}, nil
}

// Run runs the specified KubeletServer with the given Dependencies. This should never exit.
// The kubeDeps argument may be nil - if so, it is initialized from the settings on KubeletServer.
// Otherwise, the caller is assumed to have set up the Dependencies object and a default one will
// not be generated.
func Run(s *options.KubeletServer, kubeDeps *kubelet.Dependencies) error {
	if err := run(s, kubeDeps); err != nil {
		return fmt.Errorf("failed to run Kubelet: %v", err)
	}
	return nil
}

func checkPermissions() error {
	if uid := os.Getuid(); uid != 0 {
		return fmt.Errorf("Kubelet needs to run as uid `0`. It is being run as %d", uid)
	}
	// TODO: Check if kubelet is running in the `initial` user namespace.
	// http://man7.org/linux/man-pages/man7/user_namespaces.7.html
	return nil
}

func setConfigz(cz *configz.Config, kc *kubeletconfiginternal.KubeletConfiguration) error {
	scheme, _, err := kubeletscheme.NewSchemeAndCodecs()
	if err != nil {
		return err
	}
	versioned := kubeletconfigv1alpha1.KubeletConfiguration{}
	if err := scheme.Convert(kc, &versioned, nil); err != nil {
		return err
	}
	cz.Set(versioned)
	return nil
}

func initConfigz(kc *kubeletconfiginternal.KubeletConfiguration) error {
	cz, err := configz.New("kubeletconfig")
	if err != nil {
		glog.Errorf("unable to register configz: %s", err)
		return err
	}
	if err := setConfigz(cz, kc); err != nil {
		glog.Errorf("unable to register config: %s", err)
		return err
	}
	return nil
}

// makeEventRecorder sets up kubeDeps.Recorder if its nil. Its a no-op otherwise.
func makeEventRecorder(kubeDeps *kubelet.Dependencies, nodeName types.NodeName) {
	if kubeDeps.Recorder != nil {
		return
	}
	eventBroadcaster := record.NewBroadcaster()
	kubeDeps.Recorder = eventBroadcaster.NewRecorder(api.Scheme, v1.EventSource{Component: componentKubelet, Host: string(nodeName)})
	eventBroadcaster.StartLogging(glog.V(3).Infof)
	if kubeDeps.EventClient != nil {
		glog.V(4).Infof("Sending events to api server.")
		eventBroadcaster.StartRecordingToSink(&v1core.EventSinkImpl{Interface: kubeDeps.EventClient.Events("")})
	} else {
		glog.Warning("No api server defined - no events will be sent to API server.")
	}
}

func run(s *options.KubeletServer, kubeDeps *kubelet.Dependencies) (err error) {
	// Set global feature gates based on the value on the initial KubeletServer
	err = utilfeature.DefaultFeatureGate.Set(s.KubeletConfiguration.FeatureGates)
	if err != nil {
		return err
	}
	// validate the initial KubeletServer (we set feature gates first, because this validation depends on feature gates)
	if err := options.ValidateKubeletServer(s); err != nil {
		return err
	}

	// Obtain Kubelet Lock File
	if s.ExitOnLockContention && s.LockFilePath == "" {
		return errors.New("cannot exit on lock file contention: no lock file specified")
	}
	done := make(chan struct{})
	if s.LockFilePath != "" {
		glog.Infof("acquiring file lock on %q", s.LockFilePath)
		if err := flock.Acquire(s.LockFilePath); err != nil {
			return fmt.Errorf("unable to acquire file lock on %q: %v", s.LockFilePath, err)
		}
		if s.ExitOnLockContention {
			glog.Infof("watching for inotify events for: %v", s.LockFilePath)
			if err := watchForLockfileContention(s.LockFilePath, done); err != nil {
				return err
			}
		}
	}

	// Register current configuration with /configz endpoint
	err = initConfigz(&s.KubeletConfiguration)
	if err != nil {
		glog.Errorf("unable to register KubeletConfiguration with configz, error: %v", err)
	}

	// About to get clients and such, detect standaloneMode
	standaloneMode := true
	switch {
	case s.RequireKubeConfig == true:
		standaloneMode = false
		glog.Warningf("--require-kubeconfig is deprecated. Set --kubeconfig without using --require-kubeconfig.")
	case s.KubeConfig.Provided():
		standaloneMode = false
	}

	if kubeDeps == nil {
		kubeDeps, err = UnsecuredDependencies(s)
		if err != nil {
			return err
		}
	}

	if s.CloudProvider == kubeletconfigv1alpha1.AutoDetectCloudProvider {
		glog.Warning("--cloud-provider=auto-detect is deprecated. The desired cloud provider should be set explicitly")
	}

	if kubeDeps.Cloud == nil {
		if !cloudprovider.IsExternal(s.CloudProvider) && s.CloudProvider != kubeletconfigv1alpha1.AutoDetectCloudProvider {
			cloud, err := cloudprovider.InitCloudProvider(s.CloudProvider, s.CloudConfigFile)
			if err != nil {
				return err
			}
			if cloud == nil {
				glog.V(2).Infof("No cloud provider specified: %q from the config file: %q\n", s.CloudProvider, s.CloudConfigFile)
			} else {
				glog.V(2).Infof("Successfully initialized cloud provider: %q from the config file: %q\n", s.CloudProvider, s.CloudConfigFile)
			}
			kubeDeps.Cloud = cloud
		}
	}

	nodeName, err := getNodeName(kubeDeps.Cloud, nodeutil.GetHostname(s.HostnameOverride))
	if err != nil {
		return err
	}

	if s.BootstrapKubeconfig != "" {
		if err := bootstrap.LoadClientCert(s.KubeConfig.Value(), s.BootstrapKubeconfig, s.CertDirectory, nodeName); err != nil {
			return err
		}
	}

	// if in standalone mode, indicate as much by setting all clients to nil
	if standaloneMode {
		kubeDeps.KubeClient = nil
		kubeDeps.ExternalKubeClient = nil
		kubeDeps.EventClient = nil
		glog.Warningf("standalone mode, no API client")
	} else if kubeDeps.KubeClient == nil || kubeDeps.ExternalKubeClient == nil || kubeDeps.EventClient == nil {
		// initialize clients if not standalone mode and any of the clients are not provided
		var kubeClient clientset.Interface
		var eventClient v1core.EventsGetter
		var externalKubeClient clientgoclientset.Interface

		clientConfig, err := CreateAPIServerClientConfig(s)

		var clientCertificateManager certificate.Manager
		if err == nil {
			if s.RotateCertificates && utilfeature.DefaultFeatureGate.Enabled(features.RotateKubeletClientCertificate) {
				clientCertificateManager, err = certificate.NewKubeletClientCertificateManager(s.CertDirectory, nodeName, clientConfig.CertData, clientConfig.KeyData, clientConfig.CertFile, clientConfig.KeyFile)
				if err != nil {
					return err
				}
				if err := certificate.UpdateTransport(wait.NeverStop, clientConfig, clientCertificateManager); err != nil {
					return err
				}
			}

			kubeClient, err = clientset.NewForConfig(clientConfig)
			if err != nil {
				glog.Warningf("New kubeClient from clientConfig error: %v", err)
			} else if kubeClient.Certificates() != nil && clientCertificateManager != nil {
				glog.V(2).Info("Starting client certificate rotation.")
				clientCertificateManager.SetCertificateSigningRequestClient(kubeClient.Certificates().CertificateSigningRequests())
				clientCertificateManager.Start()
			}
			externalKubeClient, err = clientgoclientset.NewForConfig(clientConfig)
			if err != nil {
				glog.Warningf("New kubeClient from clientConfig error: %v", err)
			}
			// make a separate client for events
			eventClientConfig := *clientConfig
			eventClientConfig.QPS = float32(s.EventRecordQPS)
			eventClientConfig.Burst = int(s.EventBurst)
			tmpClient, err := clientgoclientset.NewForConfig(&eventClientConfig)
			if err != nil {
				glog.Warningf("Failed to create API Server client for Events: %v", err)
			}
			eventClient = tmpClient.CoreV1()

		} else {
			switch {
			case s.RequireKubeConfig:
				return fmt.Errorf("invalid kubeconfig: %v", err)
			case s.KubeConfig.Provided():
				glog.Warningf("invalid kubeconfig: %v", err)
			}
		}

		kubeDeps.KubeClient = kubeClient
		kubeDeps.ExternalKubeClient = externalKubeClient
		if eventClient != nil {
			kubeDeps.EventClient = eventClient
		}
	}

	// Alpha Dynamic Configuration Implementation;
	// if the kubelet config controller is available, inject the latest to start the config and status sync loops
	if utilfeature.DefaultFeatureGate.Enabled(features.DynamicKubeletConfig) && kubeDeps.KubeletConfigController != nil && !standaloneMode && !s.RunOnce {
		kubeDeps.KubeletConfigController.StartSync(kubeDeps.KubeClient, string(nodeName))
	}

	if kubeDeps.Auth == nil {
		auth, err := BuildAuth(nodeName, kubeDeps.ExternalKubeClient, s.KubeletConfiguration)
		if err != nil {
			return err
		}
		kubeDeps.Auth = auth
	}

	if kubeDeps.CAdvisorInterface == nil {
		kubeDeps.CAdvisorInterface, err = cadvisor.New(s.Address, uint(s.CAdvisorPort), s.ContainerRuntime, s.RootDirectory)
		if err != nil {
			return err
		}
	}

	// Setup event recorder if required.
	makeEventRecorder(kubeDeps, nodeName)

	if kubeDeps.ContainerManager == nil {
		if s.CgroupsPerQOS && s.CgroupRoot == "" {
			glog.Infof("--cgroups-per-qos enabled, but --cgroup-root was not specified.  defaulting to /")
			s.CgroupRoot = "/"
		}
		kubeReserved, err := parseResourceList(s.KubeReserved)
		if err != nil {
			return err
		}
		systemReserved, err := parseResourceList(s.SystemReserved)
		if err != nil {
			return err
		}
		var hardEvictionThresholds []evictionapi.Threshold
		// If the user requested to ignore eviction thresholds, then do not set valid values for hardEvictionThresholds here.
		if !s.ExperimentalNodeAllocatableIgnoreEvictionThreshold {
			hardEvictionThresholds, err = eviction.ParseThresholdConfig([]string{}, s.EvictionHard, "", "", "")
			if err != nil {
				return err
			}
		}
		experimentalQOSReserved, err := cm.ParseQOSReserved(s.ExperimentalQOSReserved)
		if err != nil {
			return err
		}
		kubeDeps.ContainerManager, err = cm.NewContainerManager(
			kubeDeps.Mounter,
			kubeDeps.CAdvisorInterface,
			cm.NodeConfig{
				RuntimeCgroupsName:    s.RuntimeCgroups,
				SystemCgroupsName:     s.SystemCgroups,
				KubeletCgroupsName:    s.KubeletCgroups,
				ContainerRuntime:      s.ContainerRuntime,
				CgroupsPerQOS:         s.CgroupsPerQOS,
				CgroupRoot:            s.CgroupRoot,
				CgroupDriver:          s.CgroupDriver,
				ProtectKernelDefaults: s.ProtectKernelDefaults,
				NodeAllocatableConfig: cm.NodeAllocatableConfig{
					KubeReservedCgroupName:   s.KubeReservedCgroup,
					SystemReservedCgroupName: s.SystemReservedCgroup,
					EnforceNodeAllocatable:   sets.NewString(s.EnforceNodeAllocatable...),
					KubeReserved:             kubeReserved,
					SystemReserved:           systemReserved,
					HardEvictionThresholds:   hardEvictionThresholds,
				},
				ExperimentalQOSReserved: *experimentalQOSReserved,
			},
			s.FailSwapOn,
			kubeDeps.Recorder)

		if err != nil {
			return err
		}
	}

	if err := checkPermissions(); err != nil {
		glog.Error(err)
	}

	utilruntime.ReallyCrash = s.ReallyCrashForTesting

	rand.Seed(time.Now().UTC().UnixNano())

	// TODO(vmarmol): Do this through container config.
	oomAdjuster := kubeDeps.OOMAdjuster
	if err := oomAdjuster.ApplyOOMScoreAdj(0, int(s.OOMScoreAdj)); err != nil {
		glog.Warning(err)
	}

	if err := RunKubelet(&s.KubeletFlags, &s.KubeletConfiguration, kubeDeps, s.RunOnce); err != nil {
		return err
	}

	if s.HealthzPort > 0 {
		healthz.DefaultHealthz()
		go wait.Until(func() {
			err := http.ListenAndServe(net.JoinHostPort(s.HealthzBindAddress, strconv.Itoa(int(s.HealthzPort))), nil)
			if err != nil {
				glog.Errorf("Starting health server failed: %v", err)
			}
		}, 5*time.Second, wait.NeverStop)
	}

	if s.RunOnce {
		return nil
	}

	<-done
	return nil
}

// getNodeName returns the node name according to the cloud provider
// if cloud provider is specified. Otherwise, returns the hostname of the node.
func getNodeName(cloud cloudprovider.Interface, hostname string) (types.NodeName, error) {
	if cloud == nil {
		return types.NodeName(hostname), nil
	}

	instances, ok := cloud.Instances()
	if !ok {
		return "", fmt.Errorf("failed to get instances from cloud provider")
	}

	nodeName, err := instances.CurrentNodeName(hostname)
	if err != nil {
		return "", fmt.Errorf("error fetching current node name from cloud provider: %v", err)
	}

	glog.V(2).Infof("cloud provider determined current node name to be %s", nodeName)

	return nodeName, nil
}

// InitializeTLS checks for a configured TLSCertFile and TLSPrivateKeyFile: if unspecified a new self-signed
// certificate and key file are generated. Returns a configured server.TLSOptions object.
func InitializeTLS(kf *options.KubeletFlags, kc *kubeletconfiginternal.KubeletConfiguration) (*server.TLSOptions, error) {
	if !utilfeature.DefaultFeatureGate.Enabled(features.RotateKubeletServerCertificate) && kc.TLSCertFile == "" && kc.TLSPrivateKeyFile == "" {
		kc.TLSCertFile = path.Join(kf.CertDirectory, "kubelet.crt")
		kc.TLSPrivateKeyFile = path.Join(kf.CertDirectory, "kubelet.key")

		canReadCertAndKey, err := certutil.CanReadCertAndKey(kc.TLSCertFile, kc.TLSPrivateKeyFile)
		if err != nil {
			return nil, err
		}
		if !canReadCertAndKey {
			cert, key, err := certutil.GenerateSelfSignedCertKey(nodeutil.GetHostname(kf.HostnameOverride), nil, nil)
			if err != nil {
				return nil, fmt.Errorf("unable to generate self signed cert: %v", err)
			}

			if err := certutil.WriteCert(kc.TLSCertFile, cert); err != nil {
				return nil, err
			}

			if err := certutil.WriteKey(kc.TLSPrivateKeyFile, key); err != nil {
				return nil, err
			}

			glog.V(4).Infof("Using self-signed cert (%s, %s)", kc.TLSCertFile, kc.TLSPrivateKeyFile)
		}
	}
	tlsOptions := &server.TLSOptions{
		Config: &tls.Config{
			// Can't use SSLv3 because of POODLE and BEAST
			// Can't use TLSv1.0 because of POODLE and BEAST using CBC cipher
			// Can't use TLSv1.1 because of RC4 cipher usage
			MinVersion: tls.VersionTLS12,
		},
		CertFile: kc.TLSCertFile,
		KeyFile:  kc.TLSPrivateKeyFile,
	}

	if len(kc.Authentication.X509.ClientCAFile) > 0 {
		clientCAs, err := certutil.NewPool(kc.Authentication.X509.ClientCAFile)
		if err != nil {
			return nil, fmt.Errorf("unable to load client CA file %s: %v", kc.Authentication.X509.ClientCAFile, err)
		}
		// Specify allowed CAs for client certificates
		tlsOptions.Config.ClientCAs = clientCAs
		// Populate PeerCertificates in requests, but don't reject connections without verified certificates
		tlsOptions.Config.ClientAuth = tls.RequestClientCert
	}

	return tlsOptions, nil
}

func kubeconfigClientConfig(s *options.KubeletServer) (*restclient.Config, error) {
	return clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
		&clientcmd.ClientConfigLoadingRules{ExplicitPath: s.KubeConfig.Value()},
		&clientcmd.ConfigOverrides{},
	).ClientConfig()
}

// createClientConfig creates a client configuration from the command line arguments.
// If --kubeconfig is explicitly set, it will be used. If it is not set but
// --require-kubeconfig=true, we attempt to load the default kubeconfig file.
func createClientConfig(s *options.KubeletServer) (*restclient.Config, error) {
	// If --kubeconfig was not provided, it will have a default path set in cmd/kubelet/app/options/options.go.
	// We only use that default path when --require-kubeconfig=true. The default path is temporary until --require-kubeconfig is removed.
	// TODO(#41161:v1.10.0): Remove the default kubeconfig path and --require-kubeconfig.
	if s.BootstrapKubeconfig != "" || s.KubeConfig.Provided() || s.RequireKubeConfig == true {
		return kubeconfigClientConfig(s)
	} else {
		return nil, fmt.Errorf("createClientConfig called in standalone mode")
	}
}

// CreateAPIServerClientConfig generates a client.Config from command line flags
// via createClientConfig and then injects chaos into the configuration via addChaosToClientConfig.
// This func is exported to support integration with third party kubelet extensions (e.g. kubernetes-mesos).
func CreateAPIServerClientConfig(s *options.KubeletServer) (*restclient.Config, error) {
	clientConfig, err := createClientConfig(s)
	if err != nil {
		return nil, err
	}

	clientConfig.ContentType = s.ContentType
	// Override kubeconfig qps/burst settings from flags
	clientConfig.QPS = float32(s.KubeAPIQPS)
	clientConfig.Burst = int(s.KubeAPIBurst)

	addChaosToClientConfig(s, clientConfig)
	return clientConfig, nil
}

// addChaosToClientConfig injects random errors into client connections if configured.
func addChaosToClientConfig(s *options.KubeletServer, config *restclient.Config) {
	if s.ChaosChance != 0.0 {
		config.WrapTransport = func(rt http.RoundTripper) http.RoundTripper {
			seed := chaosclient.NewSeed(1)
			// TODO: introduce a standard chaos package with more tunables - this is just a proof of concept
			// TODO: introduce random latency and stalls
			return chaosclient.NewChaosRoundTripper(rt, chaosclient.LogChaos, seed.P(s.ChaosChance, chaosclient.ErrSimulatedConnectionResetByPeer))
		}
	}
}

// RunKubelet is responsible for setting up and running a kubelet.  It is used in three different applications:
//   1 Integration tests
//   2 Kubelet binary
//   3 Standalone 'kubernetes' binary
// Eventually, #2 will be replaced with instances of #3
func RunKubelet(kubeFlags *options.KubeletFlags, kubeCfg *kubeletconfiginternal.KubeletConfiguration, kubeDeps *kubelet.Dependencies, runOnce bool) error {
	hostname := nodeutil.GetHostname(kubeFlags.HostnameOverride)
	// Query the cloud provider for our node name, default to hostname if kcfg.Cloud == nil
	nodeName, err := getNodeName(kubeDeps.Cloud, hostname)
	if err != nil {
		return err
	}
	// Setup event recorder if required.
	makeEventRecorder(kubeDeps, nodeName)

	// TODO(mtaufen): I moved the validation of these fields here, from UnsecuredKubeletConfig,
	//                so that I could remove the associated fields from KubeletConfiginternal. I would
	//                prefer this to be done as part of an independent validation step on the
	//                KubeletConfiguration. But as far as I can tell, we don't have an explicit
	//                place for validation of the KubeletConfiguration yet.
	hostNetworkSources, err := kubetypes.GetValidatedSources(kubeCfg.HostNetworkSources)
	if err != nil {
		return err
	}

	hostPIDSources, err := kubetypes.GetValidatedSources(kubeCfg.HostPIDSources)
	if err != nil {
		return err
	}

	hostIPCSources, err := kubetypes.GetValidatedSources(kubeCfg.HostIPCSources)
	if err != nil {
		return err
	}

	privilegedSources := capabilities.PrivilegedSources{
		HostNetworkSources: hostNetworkSources,
		HostPIDSources:     hostPIDSources,
		HostIPCSources:     hostIPCSources,
	}
	capabilities.Setup(kubeCfg.AllowPrivileged, privilegedSources, 0)

	credentialprovider.SetPreferredDockercfgPath(kubeFlags.RootDirectory)
	glog.V(2).Infof("Using root directory: %v", kubeFlags.RootDirectory)

	builder := kubeDeps.Builder
	if builder == nil {
		builder = CreateAndInitKubelet
	}
	if kubeDeps.OSInterface == nil {
		kubeDeps.OSInterface = kubecontainer.RealOS{}
	}

	k, err := builder(kubeCfg, kubeDeps, &kubeFlags.ContainerRuntimeOptions, kubeFlags.HostnameOverride, kubeFlags.NodeIP, kubeFlags.ProviderID, kubeFlags.CloudProvider, kubeFlags.CertDirectory, kubeFlags.RootDirectory)
	if err != nil {
		return fmt.Errorf("failed to create kubelet: %v", err)
	}

	// NewMainKubelet should have set up a pod source config if one didn't exist
	// when the builder was run. This is just a precaution.
	if kubeDeps.PodConfig == nil {
		return fmt.Errorf("failed to create kubelet, pod source config was nil")
	}
	podCfg := kubeDeps.PodConfig

	rlimit.RlimitNumFiles(uint64(kubeCfg.MaxOpenFiles))

	// process pods and exit.
	if runOnce {
		if _, err := k.RunOnce(podCfg.Updates()); err != nil {
			return fmt.Errorf("runonce failed: %v", err)
		}
		glog.Infof("Started kubelet %s as runonce", version.Get().String())
	} else {
		startKubelet(k, podCfg, kubeCfg, kubeDeps)
		glog.Infof("Started kubelet %s", version.Get().String())
	}
	return nil
}

func startKubelet(k kubelet.Bootstrap, podCfg *config.PodConfig, kubeCfg *kubeletconfiginternal.KubeletConfiguration, kubeDeps *kubelet.Dependencies) {
	// start the kubelet
	go wait.Until(func() { k.Run(podCfg.Updates()) }, 0, wait.NeverStop)

	// start the kubelet server
	if kubeCfg.EnableServer {
		go wait.Until(func() {
			k.ListenAndServe(net.ParseIP(kubeCfg.Address), uint(kubeCfg.Port), kubeDeps.TLSOptions, kubeDeps.Auth, kubeCfg.EnableDebuggingHandlers, kubeCfg.EnableContentionProfiling)
		}, 0, wait.NeverStop)
	}
	if kubeCfg.ReadOnlyPort > 0 {
		go wait.Until(func() {
			k.ListenAndServeReadOnly(net.ParseIP(kubeCfg.Address), uint(kubeCfg.ReadOnlyPort))
		}, 0, wait.NeverStop)
	}
}

func CreateAndInitKubelet(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
	kubeDeps *kubelet.Dependencies,
	crOptions *options.ContainerRuntimeOptions,
	hostnameOverride,
	nodeIP,
	providerID,
	cloudProvider,
	certDirectory,
	rootDirectory string) (k kubelet.Bootstrap, err error) {
	// TODO: block until all sources have delivered at least one update to the channel, or break the sync loop
	// up into "per source" synchronizations

	k, err = kubelet.NewMainKubelet(kubeCfg, kubeDeps, crOptions, hostnameOverride, nodeIP, providerID, cloudProvider, certDirectory, rootDirectory)
	if err != nil {
		return nil, err
	}

	k.BirthCry()

	k.StartGarbageCollection()

	return k, nil
}

// parseResourceList parses the given configuration map into an API
// ResourceList or returns an error.
func parseResourceList(m kubeletconfiginternal.ConfigurationMap) (v1.ResourceList, error) {
	if len(m) == 0 {
		return nil, nil
	}
	rl := make(v1.ResourceList)
	for k, v := range m {
		switch v1.ResourceName(k) {
		// CPU, memory and local storage resources are supported.
		case v1.ResourceCPU, v1.ResourceMemory, v1.ResourceEphemeralStorage:
			q, err := resource.ParseQuantity(v)
			if err != nil {
				return nil, err
			}
			if q.Sign() == -1 {
				return nil, fmt.Errorf("resource quantity for %q cannot be negative: %v", k, v)
			}
			rl[v1.ResourceName(k)] = q
		default:
			return nil, fmt.Errorf("cannot reserve %q resource", k)
		}
	}
	return rl, nil
}

// BootstrapKubeletConfigController constructs and bootstrap a configuration controller
func BootstrapKubeletConfigController(defaultConfig *kubeletconfiginternal.KubeletConfiguration,
	initConfigDirFlag flag.StringFlag,
	dynamicConfigDirFlag flag.StringFlag) (*kubeletconfiginternal.KubeletConfiguration, *kubeletconfig.Controller, error) {
	var err error
	// Alpha Dynamic Configuration Implementation; this section only loads config from disk, it does not contact the API server
	// compute absolute paths based on current working dir
	initConfigDir := ""
	if utilfeature.DefaultFeatureGate.Enabled(features.KubeletConfigFile) && initConfigDirFlag.Provided() {
		initConfigDir, err = filepath.Abs(initConfigDirFlag.Value())
		if err != nil {
			return nil, nil, fmt.Errorf("failed to get absolute path for --init-config-dir")
		}
	}
	dynamicConfigDir := ""
	if utilfeature.DefaultFeatureGate.Enabled(features.DynamicKubeletConfig) && dynamicConfigDirFlag.Provided() {
		dynamicConfigDir, err = filepath.Abs(dynamicConfigDirFlag.Value())
		if err != nil {
			return nil, nil, fmt.Errorf("failed to get absolute path for --dynamic-config-dir")
		}
	}

	// get the latest KubeletConfiguration checkpoint from disk, or load the init or default config if no valid checkpoints exist
	kubeletConfigController, err := kubeletconfig.NewController(defaultConfig, initConfigDir, dynamicConfigDir)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to construct controller, error: %v", err)
	}
	kubeletConfig, err := kubeletConfigController.Bootstrap()
	if err != nil {
		return nil, nil, fmt.Errorf("failed to determine a valid configuration, error: %v", err)
	}
	return kubeletConfig, kubeletConfigController, nil
}

// RunDockershim only starts the dockershim in current process. This is only used for cri validate testing purpose
// TODO(random-liu): Move this to a separate binary.
func RunDockershim(c *kubeletconfiginternal.KubeletConfiguration, r *options.ContainerRuntimeOptions) error {
	// Create docker client.
	dockerClient := libdocker.ConnectToDockerOrDie(r.DockerEndpoint, c.RuntimeRequestTimeout.Duration,
		r.ImagePullProgressDeadline.Duration)

	// Initialize network plugin settings.
	binDir := r.CNIBinDir
	if binDir == "" {
		binDir = r.NetworkPluginDir
	}
	nh := &kubelet.NoOpLegacyHost{}
	pluginSettings := dockershim.NetworkPluginSettings{
		HairpinMode:       kubeletconfiginternal.HairpinMode(c.HairpinMode),
		NonMasqueradeCIDR: c.NonMasqueradeCIDR,
		PluginName:        r.NetworkPluginName,
		PluginConfDir:     r.CNIConfDir,
		PluginBinDir:      binDir,
		MTU:               int(r.NetworkPluginMTU),
		LegacyRuntimeHost: nh,
	}

	// Initialize streaming configuration. (Not using TLS now)
	streamingConfig := &streaming.Config{
		// Use a relative redirect (no scheme or host).
		BaseURL:                         &url.URL{Path: "/cri/"},
		StreamIdleTimeout:               c.StreamingConnectionIdleTimeout.Duration,
		StreamCreationTimeout:           streaming.DefaultConfig.StreamCreationTimeout,
		SupportedRemoteCommandProtocols: streaming.DefaultConfig.SupportedRemoteCommandProtocols,
		SupportedPortForwardProtocols:   streaming.DefaultConfig.SupportedPortForwardProtocols,
	}

	ds, err := dockershim.NewDockerService(dockerClient, r.PodSandboxImage, streamingConfig, &pluginSettings,
		c.RuntimeCgroups, c.CgroupDriver, r.DockerExecHandlerName, r.DockershimRootDirectory, r.DockerDisableSharedPID)
	if err != nil {
		return err
	}
	if err := ds.Start(); err != nil {
		return err
	}

	glog.V(2).Infof("Starting the GRPC server for the docker CRI shim.")
	server := dockerremote.NewDockerServer(c.RemoteRuntimeEndpoint, ds)
	if err := server.Start(); err != nil {
		return err
	}

	// Start the streaming server
	addr := net.JoinHostPort(c.Address, strconv.Itoa(int(c.Port)))
	return http.ListenAndServe(addr, ds)
}