checkpointer: implement state machine.

This implements an explicit state machine to capture the various states
a checkpoint can be in. It recovers those states from disk upon startup
(if applicable) and then reconciles them with the states that are
fetched from the various apiservers.

It also adds 2 new states to attempt to work around issues with
kubernetes 1.8 in which daemonset pods are deleted before being
recreated. For single-master clusters this can lead to a total outage
during apiserver upgrades since the checkpointer will aggressively
retire the checkpoint for the deleted apiserver pod before it has
a chance to schedule the new one.

Author: diegs

pkg/checkpoint/apiserver.go

@@ -9,15 +9,16 @@ import (
 )
 
 // getAPIParentPods will retrieve all pods from apiserver that are parents & should be checkpointed
-func (c *checkpointer) getAPIParentPods(nodeName string) map[string]*v1.Pod {
+// Returns false if we could not contact the apiserver.
+func (c *checkpointer) getAPIParentPods(nodeName string) (bool, map[string]*v1.Pod) {
 	opts := metav1.ListOptions{
 		FieldSelector: fields.OneTermEqualSelector(api.PodHostField, nodeName).String(),
 	}
 
 	podList, err := c.apiserver.CoreV1().Pods(api.NamespaceAll).List(opts)
 	if err != nil {
 		glog.Warningf("Unable to contact APIServer, skipping garbage collection: %v", err)
-		return nil
+		return false, nil
 	}
-	return podListToParentPods(podList)
+	return true, podListToParentPods(podList)
 }

pkg/checkpoint/checkpoint.go

@@ -4,8 +4,10 @@ package checkpoint
 
 import (
 	"fmt"
+	"os"
 	"time"
 
+	"github.com/golang/glog"
 	"k8s.io/client-go/kubernetes"
 	restclient "k8s.io/client-go/rest"
 )
@@ -23,12 +25,14 @@ const (
 	shouldCheckpoint = "true"
 	podSourceFile    = "file"
 
-	defaultPollingFrequency  = 3 * time.Second
-	defaultCheckpointTimeout = 1 * time.Minute
+	defaultPollingFrequency      = 5 * time.Second
+	defaultCheckpointTimeout     = 1 * time.Minute
+	defaultCheckpointGracePeriod = 1 * time.Minute
 )
 
 var (
-	lastCheckpoint time.Time
+	lastCheckpoint        time.Time
+	checkpointGracePeriod = defaultCheckpointGracePeriod
 )
 
 // Options defines the parameters that are required to start the checkpointer.
@@ -59,6 +63,7 @@ type checkpointer struct {
 	kubelet         *kubeletClient
 	cri             *remoteRuntimeService
 	checkpointerPod CheckpointerPod
+	checkpoints     checkpoints
 }
 
 // Run instantiates and starts a new checkpointer. Returns error if there was a problem creating
@@ -90,6 +95,11 @@ func Run(opts Options) error {
 
 // run is the main checkpointing loop.
 func (c *checkpointer) run() {
+	// Make sure the inactive checkpoint path exists.
+	if err := os.MkdirAll(inactiveCheckpointPath, 0700); err != nil {
+		glog.Fatalf("Could not create inactive checkpoint path: %v", err)
+	}
+
 	for {
 		time.Sleep(defaultPollingFrequency)
 
@@ -101,20 +111,24 @@ func (c *checkpointer) run() {
 		localParentPods := c.kubelet.localParentPods()
 		localRunningPods := c.cri.localRunningPods()
 
-		c.createCheckpointsForValidParents(localParentPods)
-
 		// Try to get scheduled pods from the apiserver.
 		// These will be used to GC checkpoints for parents no longer scheduled to this node.
-		// A return value of nil is assumed to be "could not contact apiserver"
 		// TODO(aaron): only check this every 30 seconds or so
-		apiParentPods := c.getAPIParentPods(c.checkpointerPod.NodeName)
+		apiAvailable, apiParentPods := c.getAPIParentPods(c.checkpointerPod.NodeName)
 
 		// Get on disk copies of (in)active checkpoints
 		//TODO(aaron): Could be racy to load from disk each time, but much easier than trying to keep in-memory state in sync.
 		activeCheckpoints := getFileCheckpoints(activeCheckpointPath)
 		inactiveCheckpoints := getFileCheckpoints(inactiveCheckpointPath)
 
-		start, stop, remove := process(localRunningPods, localParentPods, apiParentPods, activeCheckpoints, inactiveCheckpoints, c.checkpointerPod)
+		// Update checkpoints using the latest information from the APIs.
+		c.checkpoints.update(localRunningPods, localParentPods, apiParentPods, activeCheckpoints, inactiveCheckpoints, c.checkpointerPod)
+
+		// Update on-disk manifests based on updated checkpoint state.
+		c.createCheckpointsForValidParents()
+
+		// Update checkpoint states and determine which checkpoints to start, stop, or remove.
+		start, stop, remove := c.checkpoints.process(time.Now(), apiAvailable, localRunningPods, localParentPods, apiParentPods)
 
 		// Handle remove at last because we may still have some work to do
 		// before removing the checkpointer itself.

pkg/checkpoint/manifest.go

@@ -52,10 +52,6 @@ func writeCheckpointManifest(pod *v1.Pod) (bool, error) {
 		return false, err
 	}
 	path := filepath.Join(inactiveCheckpointPath, pod.Namespace+"-"+pod.Name+".json")
-	// Make sure the inactive checkpoint path exists.
-	if err := os.MkdirAll(filepath.Dir(path), 0600); err != nil {
-		return false, err
-	}
 	return writeManifestIfDifferent(path, podFullName(pod), buff.Bytes())
 }