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// Copyright 2017 Google LLC. All Rights Reserved.
//
// 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 election
import (
"context"
"fmt"
"math/rand"
"time"
"github.com/google/trillian/util/clock"
"github.com/google/trillian/util/election2"
"k8s.io/klog/v2"
)
// Minimum values for configuration intervals.
// TODO(pavelkalinnikov): These parameters are specific to the application, so
// shouldn't be here.
const (
MinPreElectionPause = 10 * time.Millisecond
MinMasterHoldInterval = 10 * time.Second
)
// RunnerConfig describes the parameters for an election Runner.
type RunnerConfig struct {
// PreElectionPause is the maximum interval to wait before starting a
// mastership election for a particular log.
PreElectionPause time.Duration
// MasterHoldInterval is the minimum interval to hold mastership for.
MasterHoldInterval time.Duration
// MasterHoldJitter is the maximum addition to MasterHoldInterval.
MasterHoldJitter time.Duration
TimeSource clock.TimeSource
}
// ResignDelay returns a randomized delay of how long to keep mastership for.
func (cfg *RunnerConfig) ResignDelay() time.Duration {
delay := cfg.MasterHoldInterval
if cfg.MasterHoldJitter <= 0 {
return delay
}
add := rand.Int63n(int64(cfg.MasterHoldJitter))
return delay + time.Duration(add)
}
// fixupRunnerConfig ensures operation parameters have required minimum values.
func fixupRunnerConfig(cfg *RunnerConfig) {
if cfg.PreElectionPause < MinPreElectionPause {
cfg.PreElectionPause = MinPreElectionPause
}
if cfg.MasterHoldInterval < MinMasterHoldInterval {
cfg.MasterHoldInterval = MinMasterHoldInterval
}
if cfg.MasterHoldJitter < 0 {
cfg.MasterHoldJitter = 0
}
if cfg.TimeSource == nil {
cfg.TimeSource = clock.System
}
}
// Runner controls a continuous election process.
type Runner struct {
// Allow the user to store a Cancel function with the runner for convenience.
Cancel context.CancelFunc
id string
cfg *RunnerConfig
tracker *MasterTracker
election election2.Election
}
// NewRunner builds a new election Runner instance with the given config. On
// calling Run(), the provided Election will be continuously monitored, and
// mastership changes will be notified to the provided MasterTracker instance.
func NewRunner(id string, cfg *RunnerConfig, tracker *MasterTracker, cancel context.CancelFunc, el election2.Election) *Runner {
fixupRunnerConfig(cfg)
return &Runner{
Cancel: cancel,
id: id,
cfg: cfg,
tracker: tracker,
election: el,
}
}
// Run performs a continuous election process. It runs continuously until the
// context is canceled or an internal error is encountered.
func (er *Runner) Run(ctx context.Context, pending chan<- Resignation) {
// Pause for a random interval so that if multiple instances start at the
// same time there is less of a thundering herd.
pause := rand.Int63n(er.cfg.PreElectionPause.Nanoseconds())
if err := clock.SleepSource(ctx, time.Duration(pause), er.cfg.TimeSource); err != nil {
return // The context has been canceled during the sleep.
}
klog.V(1).Infof("%s: start election-monitoring loop ", er.id)
defer func() {
klog.Infof("%s: shutdown election-monitoring loop", er.id)
if err := er.election.Close(ctx); err != nil {
klog.Warningf("%s: election.Close: %v", er.id, err)
}
}()
for {
if err := er.beMaster(ctx, pending); err != nil {
klog.Errorf("%s: %v", er.id, err)
break
}
}
}
func (er *Runner) beMaster(ctx context.Context, pending chan<- Resignation) error {
klog.V(1).Infof("%s: When I left you, I was but the learner", er.id)
if err := er.election.Await(ctx); err != nil {
return fmt.Errorf("election.Await() failed: %v", err)
}
klog.Infof("%s: Now, I am the master", er.id)
er.tracker.Set(er.id, true)
defer er.tracker.Set(er.id, false)
mctx, err := er.election.WithMastership(ctx)
if err != nil {
return fmt.Errorf("election.WithMastership() failed: %v", err)
}
timer := er.cfg.TimeSource.NewTimer(er.cfg.ResignDelay())
defer timer.Stop()
select {
case <-mctx.Done(): // Mastership context is canceled.
klog.Errorf("%s: no longer the master!", er.id)
return mctx.Err()
case <-timer.Chan():
klog.Infof("%s: queue up resignation of mastership", er.id)
done := make(chan struct{})
r := Resignation{ID: er.id, er: er, done: done}
select {
case pending <- r:
<-done // Block until acted on.
default:
klog.Warning("Dropping resignation because operation manager seems to be exiting")
}
}
return nil
}
// Resignation indicates that a master should explicitly resign mastership, and
// call the Execute() method as soon as no master-related activity is ongoing.
type Resignation struct {
ID string
er *Runner
done chan<- struct{}
}
// Execute performs the pending deliberate resignation for an election runner.
func (r *Resignation) Execute(ctx context.Context) {
defer close(r.done)
klog.Infof("%s: deliberately resigning mastership", r.er.id)
if err := r.er.election.Resign(ctx); err != nil {
klog.Errorf("%s: failed to resign mastership: %v", r.er.id, err)
}
}
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