controller.go

/*
Copyright 2017 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 kubeletconfig

import (
	"fmt"
	"path/filepath"
	"time"

	"k8s.io/apimachinery/pkg/util/wait"
	clientset "k8s.io/client-go/kubernetes"
	v1core "k8s.io/client-go/kubernetes/typed/core/v1"
	"k8s.io/client-go/tools/cache"
	"k8s.io/kubernetes/pkg/kubelet/apis/kubeletconfig"
	"k8s.io/kubernetes/pkg/kubelet/apis/kubeletconfig/validation"

	"k8s.io/kubernetes/pkg/kubelet/kubeletconfig/checkpoint"
	"k8s.io/kubernetes/pkg/kubelet/kubeletconfig/checkpoint/store"
	"k8s.io/kubernetes/pkg/kubelet/kubeletconfig/status"
	utillog "k8s.io/kubernetes/pkg/kubelet/kubeletconfig/util/log"
	utilpanic "k8s.io/kubernetes/pkg/kubelet/kubeletconfig/util/panic"
	utilfs "k8s.io/kubernetes/pkg/util/filesystem"
)

const (
	storeDir = "store"
	// TODO(mtaufen): We may expose this in a future API, but for the time being we use an internal default,
	// because it is not especially clear where this should live in the API.
	configTrialDuration = 10 * time.Minute
)

// Controller manages syncing dynamic Kubelet configurations
// For more information, see the proposal: https://github.com/kubernetes/community/blob/master/contributors/design-proposals/node/dynamic-kubelet-configuration.md
type Controller struct {
	// pendingConfigSource; write to this channel to indicate that the config source needs to be synced from the API server
	pendingConfigSource chan bool

	// configStatus manages the status we report on the Node object
	configStatus status.NodeConfigStatus

	// informer is the informer that watches the Node object
	informer cache.SharedInformer

	// checkpointStore persists config source checkpoints to a storage layer
	checkpointStore store.Store
}

// NewController constructs a new Controller object and returns it. Directory paths must be absolute.
func NewController(dynamicConfigDir string) *Controller {
	return &Controller{
		// channels must have capacity at least 1, since we signal with non-blocking writes
		pendingConfigSource: make(chan bool, 1),
		configStatus:        status.NewNodeConfigStatus(),
		checkpointStore:     store.NewFsStore(utilfs.DefaultFs{}, filepath.Join(dynamicConfigDir, storeDir)),
	}
}

// Bootstrap attempts to return a valid KubeletConfiguration based on the configuration of the Controller,
// or returns an error if no valid configuration could be produced. Bootstrap should be called synchronously before StartSync.
func (cc *Controller) Bootstrap() (*kubeletconfig.KubeletConfiguration, error) {
	utillog.Infof("starting controller")

	// ensure the filesystem is initialized
	if err := cc.initializeDynamicConfigDir(); err != nil {
		return nil, err
	}

	// determine assigned source and set status
	assignedSource, err := cc.checkpointStore.Assigned()
	if err != nil {
		return nil, err
	}
	if assignedSource != nil {
		cc.configStatus.SetAssigned(assignedSource.NodeConfigSource())
	}

	// determine last-known-good source and set status
	lastKnownGoodSource, err := cc.checkpointStore.LastKnownGood()
	if err != nil {
		return nil, err
	}
	if lastKnownGoodSource != nil {
		cc.configStatus.SetLastKnownGood(lastKnownGoodSource.NodeConfigSource())
	}

	// if the assigned source is nil, return nil to indicate local config
	if assignedSource == nil {
		return nil, nil
	}

	// attempt to load assigned config
	assignedConfig, reason, err := cc.loadConfig(assignedSource)
	if err == nil {
		// update the active source to the non-nil assigned source
		cc.configStatus.SetActive(assignedSource.NodeConfigSource())

		// update the last-known-good config if necessary, and start a timer that
		// periodically checks whether the last-known good needs to be updated
		// we only do this when the assigned config loads and passes validation
		// wait.Forever will call the func once before starting the timer
		go wait.Forever(func() { cc.checkTrial(configTrialDuration) }, 10*time.Second)

		return assignedConfig, nil
	} // Assert: the assigned config failed to load or validate

	// TODO(mtaufen): consider re-attempting download when a load/verify/parse/validate
	// error happens outside trial period, we already made it past the trial so it's probably filesystem corruption
	// or something else scary

	// log the reason and error details for the failure to load the assigned config
	utillog.Errorf(fmt.Sprintf("%s, error: %v", reason, err))

	// set status to indicate the failure with the assigned config
	cc.configStatus.SetError(reason)

	// if the last-known-good source is nil, return nil to indicate local config
	if lastKnownGoodSource == nil {
		return nil, nil
	}

	// attempt to load the last-known-good config
	lastKnownGoodConfig, _, err := cc.loadConfig(lastKnownGoodSource)
	if err != nil {
		// we failed to load the last-known-good, so something is really messed up and we just return the error
		return nil, err
	}

	// update the active source to the non-nil last-known-good source
	cc.configStatus.SetActive(lastKnownGoodSource.NodeConfigSource())
	return lastKnownGoodConfig, nil
}

// StartSync launches the controller's sync loops if `client` is non-nil and `nodeName` is non-empty.
// It will always start the Node condition reporting loop, and will also start the dynamic conifg sync loops
// if dynamic config is enabled on the controller. If `nodeName` is empty but `client` is non-nil, an error is logged.
func (cc *Controller) StartSync(client clientset.Interface, eventClient v1core.EventsGetter, nodeName string) {
	if client == nil {
		utillog.Infof("nil client, will not start sync loops")
		return
	} else if len(nodeName) == 0 {
		utillog.Errorf("cannot start sync loops with empty nodeName")
		return
	}

	// start the status sync loop
	go utilpanic.HandlePanic(func() {
		utillog.Infof("starting status sync loop")
		wait.JitterUntil(func() {
			cc.configStatus.Sync(client, nodeName)
		}, 10*time.Second, 0.2, true, wait.NeverStop)
	})()

	cc.informer = newSharedNodeInformer(client, nodeName,
		cc.onAddNodeEvent, cc.onUpdateNodeEvent, cc.onDeleteNodeEvent)
	// start the informer loop
	// Rather than use utilruntime.HandleCrash, which doesn't actually crash in the Kubelet,
	// we use HandlePanic to manually call the panic handlers and then crash.
	// We have a better chance of recovering normal operation if we just restart the Kubelet in the event
	// of a Go runtime error.
	go utilpanic.HandlePanic(func() {
		utillog.Infof("starting Node informer sync loop")
		cc.informer.Run(wait.NeverStop)
	})()

	// start the config source sync loop
	go utilpanic.HandlePanic(func() {
		utillog.Infof("starting config source sync loop")
		wait.JitterUntil(func() {
			cc.syncConfigSource(client, eventClient, nodeName)
		}, 10*time.Second, 0.2, true, wait.NeverStop)
	})()

}

// loadConfig loads Kubelet config from a checkpoint
// It returns the loaded configuration or a clean failure reason (for status reporting) and an error.
func (cc *Controller) loadConfig(source checkpoint.RemoteConfigSource) (*kubeletconfig.KubeletConfiguration, string, error) {
	// load KubeletConfiguration from checkpoint
	kc, err := cc.checkpointStore.Load(source)
	if err != nil {
		return nil, status.LoadError, err
	}
	if err := validation.ValidateKubeletConfiguration(kc); err != nil {
		return nil, status.ValidateError, err
	}
	return kc, "", nil
}

// initializeDynamicConfigDir makes sure that the storage layers for various controller components are set up correctly
func (cc *Controller) initializeDynamicConfigDir() error {
	utillog.Infof("ensuring filesystem is set up correctly")
	// initializeDynamicConfigDir local checkpoint storage location
	return cc.checkpointStore.Initialize()
}

// checkTrial checks whether the trial duration has passed, and updates the last-known-good config if necessary
func (cc *Controller) checkTrial(duration time.Duration) {
	// when the trial period is over, the assigned config becomes the last-known-good
	if trial, err := cc.inTrial(duration); err != nil {
		utillog.Errorf("failed to check trial period for assigned config, error: %v", err)
	} else if !trial {
		utillog.Infof("assigned config passed trial period, will set as last-known-good")
		if err := cc.graduateAssignedToLastKnownGood(); err != nil {
			utillog.Errorf("failed to set last-known-good to assigned config, error: %v", err)
		}
	}
}

// inTrial returns true if the time elapsed since the last modification of the assigned config does not exceed `trialDur`, false otherwise
func (cc *Controller) inTrial(trialDur time.Duration) (bool, error) {
	now := time.Now()
	t, err := cc.checkpointStore.AssignedModified()
	if err != nil {
		return false, err
	}
	if now.Sub(t) <= trialDur {
		return true, nil
	}
	return false, nil
}

// graduateAssignedToLastKnownGood sets the last-known-good in the checkpointStore
// to the same value as the assigned config maintained by the checkpointStore
func (cc *Controller) graduateAssignedToLastKnownGood() error {
	// get the assigned config
	assigned, err := cc.checkpointStore.Assigned()
	if err != nil {
		return err
	}
	// update the last-known-good config
	err = cc.checkpointStore.SetLastKnownGood(assigned)
	if err != nil {
		return err
	}
	// update the status to reflect the new last-known-good config
	cc.configStatus.SetLastKnownGood(assigned.NodeConfigSource())
	return nil
}