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[release-1.25] Add jitter to scheduled snapshots and retry harder on conflicts #6782

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Jan 26, 2023
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[release-1.25] Add jitter to scheduled snapshots and retry harder on conflicts #6782

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32 changes: 28 additions & 4 deletions pkg/etcd/etcd.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ import (
"fmt"
"io"
"io/fs"
"math/rand"
"net"
"net/http"
"net/url"
Expand Down Expand Up @@ -49,6 +50,7 @@ import (
apierrors "k8s.io/apimachinery/pkg/api/errors"
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
utilnet "k8s.io/apimachinery/pkg/util/net"
"k8s.io/apimachinery/pkg/util/wait"
"k8s.io/client-go/util/retry"
)

Expand All @@ -58,6 +60,10 @@ const (
learnerMaxStallTime = time.Minute * 5
memberRemovalTimeout = time.Minute * 1

// snapshotJitterMax defines the maximum time skew on cron-triggered snapshots. The actual jitter
// will be a random Duration somewhere between 0 and snapshotJitterMax.
snapshotJitterMax = time.Second * 5

// defaultDialTimeout is intentionally short so that connections timeout within the testTimeout defined above
defaultDialTimeout = 2 * time.Second
// other defaults from k8s.io/apiserver/pkg/storage/storagebackend/factory/etcd3.go
Expand All @@ -81,6 +87,19 @@ var (
snapshotExtraMetadataConfigMapName = version.Program + "-etcd-snapshot-extra-metadata"
snapshotConfigMapName = version.Program + "-etcd-snapshots"

// snapshotDataBackoff will retry at increasing steps for up to ~30 seconds.
// If the ConfigMap update fails, the list won't be reconciled again until next time
// the server starts, so we should be fairly persistent in retrying.
snapshotDataBackoff = wait.Backoff{
Steps: 9,
Duration: 10 * time.Millisecond,
Factor: 3.0,
Jitter: 0.1,
}

// cronLogger wraps logrus's Printf output as cron-compatible logger
cronLogger = cron.VerbosePrintfLogger(logrus.StandardLogger())

NodeNameAnnotation = "etcd." + version.Program + ".cattle.io/node-name"
NodeAddressAnnotation = "etcd." + version.Program + ".cattle.io/node-address"

Expand Down Expand Up @@ -139,7 +158,7 @@ func errNotMember() error { return &MembershipError{} }
// ETCD with an initialized cron value.
func NewETCD() *ETCD {
return &ETCD{
cron: cron.New(),
cron: cron.New(cron.WithLogger(cronLogger)),
}
}

Expand Down Expand Up @@ -1712,7 +1731,7 @@ func (e *ETCD) DeleteSnapshots(ctx context.Context, snapshots []string) error {
// AddSnapshotData adds the given snapshot file information to the snapshot configmap, using the existing extra metadata
// available at the time.
func (e *ETCD) addSnapshotData(sf snapshotFile) error {
return retry.OnError(retry.DefaultBackoff, func(err error) bool {
return retry.OnError(snapshotDataBackoff, func(err error) bool {
return apierrors.IsConflict(err) || apierrors.IsAlreadyExists(err)
}, func() error {
// make sure the core.Factory is initialized. There can
Expand Down Expand Up @@ -1920,11 +1939,16 @@ func (e *ETCD) ReconcileSnapshotData(ctx context.Context) error {

// setSnapshotFunction schedules snapshots at the configured interval.
func (e *ETCD) setSnapshotFunction(ctx context.Context) {
e.cron.AddFunc(e.config.EtcdSnapshotCron, func() {
skipJob := cron.SkipIfStillRunning(cronLogger)
e.cron.AddJob(e.config.EtcdSnapshotCron, skipJob(cron.FuncJob(func() {
// Add a small amount of jitter to the actual snapshot execution. On clusters with multiple servers,
// having all the nodes take a snapshot at the exact same time can lead to excessive retry thrashing
// when updating the snapshot list configmap.
time.Sleep(time.Duration(rand.Float64() * float64(snapshotJitterMax)))
if err := e.Snapshot(ctx, e.config); err != nil {
logrus.Error(err)
}
})
})))
}

// Restore performs a restore of the ETCD datastore from
Expand Down