Add leader election config to runtime

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

runtime/leaderelection/leaderelection.go

@@ -0,0 +1,73 @@
+/*
+Copyright 2021 The Flux 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 leaderelection
+
+import (
+	"time"
+
+	"github.com/spf13/pflag"
+)
+
+const (
+	flagEnable          = "enable-leader-election"
+	flagReleaseOnCancel = "leader-election-release-on-cancel"
+	flagLeaseDuration   = "leader-election-lease-duration"
+	flagRenewDeadline   = "leader-election-renew-deadline"
+	flagRetryPeriod     = "leader-election-retry-period"
+)
+
+// Options contains the configuration options for the leader election.
+type Options struct {
+	// Enable determines whether or not to use leader election when
+	// starting the manager.
+	Enable bool
+
+	// ReleaseOnCancel defines if the leader should step down voluntarily
+	// when the Manager ends. This requires the binary to immediately end when the
+	// Manager is stopped, otherwise this setting is unsafe. Setting this significantly
+	// speeds up voluntary leader transitions as the new leader doesn't have to wait
+	// LeaseDuration time first.
+	ReleaseOnCancel bool
+
+	// LeaseDuration is the duration that non-leader candidates will
+	// wait to force acquire leadership. This is measured against time of
+	// last observed ack. Default is 30 seconds.
+	LeaseDuration time.Duration
+
+	// RenewDeadline is the duration that the acting controlplane will retry
+	// refreshing leadership before giving up. Default is 60 seconds.
+	RenewDeadline time.Duration
+
+	// RetryPeriod is the duration the LeaderElector clients should wait
+	// between tries of actions. Default is 5 seconds.
+	RetryPeriod time.Duration
+}
+
+// BindFlags will parse the given flagset for leader election option flags
+// and set the Options accordingly.
+func (o *Options) BindFlags(fs *pflag.FlagSet) {
+	fs.BoolVar(&o.Enable, flagEnable, false,
+		"Enable leader election for controller manager. Enabling this will ensure there is only one active controller manager.")
+	fs.BoolVar(&o.ReleaseOnCancel, flagReleaseOnCancel, true,
+		"Defines if the leader should step down voluntarily on controller manager shutdown.")
+	fs.DurationVar(&o.LeaseDuration, flagLeaseDuration, 30*time.Second,
+		"Interval at which non-leader candidates will wait to force acquire leadership (duration string).")
+	fs.DurationVar(&o.RenewDeadline, flagRenewDeadline, 60*time.Second,
+		"Duration that the leading controller manager will retry refreshing leadership before giving up (duration string).")
+	fs.DurationVar(&o.RetryPeriod, flagRetryPeriod, 5*time.Second,
+		"Duration the LeaderElector clients should wait between tries of actions (duration string).")
+}