Add periodic background snapshot reconcile

pkg/cli/cmds/server.go

@@ -92,6 +92,7 @@ type Server struct {
 	EtcdExposeMetrics        bool
 	EtcdSnapshotDir          string
 	EtcdSnapshotCron         string
+	EtcdSnapshotReconcile    time.Duration
 	EtcdSnapshotRetention    int
 	EtcdSnapshotCompress     bool
 	EtcdListFormat           string
@@ -390,6 +391,12 @@ var ServerFlags = []cli.Flag{
 		Destination: &ServerConfig.EtcdSnapshotCron,
 		Value:       "0 */12 * * *",
 	},
+	&cli.DurationFlag{
+		Name:        "etcd-snapshot-reconcile-interval",
+		Usage:       "(db) Snapshot reconcile interval",
+		Destination: &ServerConfig.EtcdSnapshotReconcile,
+		Value:       10 * time.Minute,
+	},
 	&cli.IntFlag{
 		Name:        "etcd-snapshot-retention",
 		Usage:       "(db) Number of snapshots to retain",

pkg/cli/server/server.go

@@ -184,12 +184,19 @@ func run(app *cli.Context, cfg *cmds.Server, leaderControllers server.CustomCont
 	serverConfig.ControlConfig.VModule = cmds.LogConfig.VModule
 
 	if !cfg.EtcdDisableSnapshots || cfg.ClusterReset {
+		if cfg.EtcdSnapshotReconcile <= 0 {
+			return errors.New("etcd-snapshot-reconcile-interval must be greater than 0s")
+		}
 		serverConfig.ControlConfig.EtcdSnapshotCompress = cfg.EtcdSnapshotCompress
 		serverConfig.ControlConfig.EtcdSnapshotName = cfg.EtcdSnapshotName
 		serverConfig.ControlConfig.EtcdSnapshotCron = cfg.EtcdSnapshotCron
 		serverConfig.ControlConfig.EtcdSnapshotDir = cfg.EtcdSnapshotDir
+		serverConfig.ControlConfig.EtcdSnapshotReconcile = metav1.Duration{Duration: cfg.EtcdSnapshotReconcile}
 		serverConfig.ControlConfig.EtcdSnapshotRetention = cfg.EtcdSnapshotRetention
 		if cfg.EtcdS3 {
+			if cfg.EtcdS3Timeout <= 0 {
+				return errors.New("etcd-s3-timeout must be greater than 0s")
+			}
 			serverConfig.ControlConfig.EtcdS3 = &config.EtcdS3{
 				AccessKey:     cfg.EtcdS3AccessKey,
 				Bucket:        cfg.EtcdS3BucketName,

pkg/cluster/cluster.go

@@ -3,7 +3,6 @@ package cluster
 import (
 	"context"
 	"net/url"
-	"runtime"
 	"strings"
 	"time"
 
@@ -44,53 +43,61 @@ func (c *Cluster) Start(ctx context.Context) (<-chan struct{}, error) {
 		return ready, nil
 	}
 
-	// start managed database (if necessary)
+	// start managed etcd database; when kine is in use this is a no-op.
 	if err := c.start(ctx); err != nil {
 		return nil, pkgerrors.WithMessage(err, "start managed database")
 	}
 
-	// get the wait channel for testing managed database readiness
-	ready, err := c.testClusterDB(ctx)
-	if err != nil {
-		return nil, err
-	}
+	// get the wait channel for testing etcd server readiness; when kine is in
+	// use the channel is closed immediately.
+	ready := c.testClusterDB(ctx)
 
+	// set c.config.Datastore and c.config.Runtime.EtcdConfig with values
+	// necessary to build etcd clients, and start kine listener if necessary.
 	if err := c.startStorage(ctx, false); err != nil {
 		return nil, err
 	}
 
-	// if necessary, store bootstrap data to datastore
+	// if necessary, store bootstrap data to datastore. saveBootstrap is only set
+	// when using kine, so this can be done before the ready channel has been closed.
 	if c.saveBootstrap {
 		if err := Save(ctx, c.config, false); err != nil {
 			return nil, err
 		}
 	}
 
-	// at this point, if etcd is in use, it's bootstrapping is complete
-	// so save the bootstrap data. We will need for etcd to be up. If
-	// the save call returns an error, we panic since subsequent etcd
-	// snapshots will be empty.
 	if c.managedDB != nil {
 		go func() {
 			for {
 				select {
 				case <-ready:
+					// always save to managed etcd, to ensure that any file modified locally are in sync with the datastore.
+					// this will panic if multiple keys exist, to prevent nodes from running with different bootstrap data.
 					if err := Save(ctx, c.config, false); err != nil {
 						panic(err)
 					}
 
 					if !c.config.EtcdDisableSnapshots {
-						_ = wait.PollUntilContextCancel(ctx, time.Second, true, func(ctx context.Context) (bool, error) {
-							err := c.managedDB.ReconcileSnapshotData(ctx)
-							if err != nil {
+						// do an initial reconcile of snapshots with a fast retry until it succeeds
+						wait.PollUntilContextCancel(ctx, time.Second, true, func(ctx context.Context) (bool, error) {
+							if err := c.managedDB.ReconcileSnapshotData(ctx); err != nil {
 								logrus.Errorf("Failed to record snapshots for cluster: %v", err)
+								return false, nil
 							}
-							return err == nil, nil
+							return true, nil
 						})
+
+						// continue reconciling snapshots in the background at the configured interval.
+						// the interval is jittered by 5% to avoid all nodes reconciling at the same time.
+						wait.JitterUntilWithContext(ctx, func(ctx context.Context) {
+							if err := c.managedDB.ReconcileSnapshotData(ctx); err != nil {
+								logrus.Errorf("Failed to record snapshots for cluster: %v", err)
 							}
+						}, c.config.EtcdSnapshotReconcile.Duration, 0.05, false)
+					}
+					return
+				case <-ctx.Done():
 					return
-				default:
-					runtime.Gosched()
 				}
 			}
 		}()

pkg/cluster/managed.go

@@ -25,11 +25,11 @@ import (
 
 // testClusterDB returns a channel that will be closed when the datastore connection is available.
 // The datastore is tested for readiness every 5 seconds until the test succeeds.
-func (c *Cluster) testClusterDB(ctx context.Context) (<-chan struct{}, error) {
+func (c *Cluster) testClusterDB(ctx context.Context) <-chan struct{} {
 	result := make(chan struct{})
 	if c.managedDB == nil {
 		close(result)
-		return result, nil
+		return result
 	}
 
 	go func() {
@@ -50,7 +50,7 @@ func (c *Cluster) testClusterDB(ctx context.Context) (<-chan struct{}, error) {
 		}
 	}()
 
-	return result, nil
+	return result
 }
 
 // start starts the database, unless a cluster reset has been requested, in which case

pkg/daemons/config/types.go

@@ -242,6 +242,7 @@ type Control struct {
 	EtcdExposeMetrics        bool            `json:"-"`
 	EtcdSnapshotDir          string          `json:"-"`
 	EtcdSnapshotCron         string          `json:"-"`
+	EtcdSnapshotReconcile    metav1.Duration `json:"-"`
 	EtcdSnapshotRetention    int             `json:"-"`
 	EtcdSnapshotCompress     bool            `json:"-"`
 	EtcdListFormat           string          `json:"-"`

pkg/etcd/etcd_linux_test.go

@@ -31,6 +31,7 @@ import (
 	healthpb "google.golang.org/grpc/health/grpc_health_v1"
 	"google.golang.org/grpc/reflection"
 	"google.golang.org/grpc/status"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	utilnet "k8s.io/apimachinery/pkg/util/net"
 	"k8s.io/apimachinery/pkg/util/wait"
 )
@@ -67,6 +68,7 @@ func generateTestConfig() *config.Control {
 		DataDir:               "/tmp/k3s/", // Different than the default value
 		EtcdSnapshotName:      "etcd-snapshot",
 		EtcdSnapshotCron:      "0 */12 * * *",
+		EtcdSnapshotReconcile: metav1.Duration{Duration: 10 * time.Minute},
 		EtcdSnapshotRetention: 5,
 		EtcdS3: &config.EtcdS3{
 			Endpoint: "s3.amazonaws.com",