Move jobs backoff back into traefik

https://github.com/cenk/backoff/pull/27#issuecomment-245842725

job/job.go

@@ -0,0 +1,39 @@
+package job
+
+import (
+	"github.com/cenk/backoff"
+	"time"
+)
+
+var (
+	_ backoff.BackOff = (*BackOff)(nil)
+)
+
+const (
+	defaultMinJobInterval = 30 * time.Second
+)
+
+// BackOff is an exponential backoff implementation for long running jobs.
+// In long running jobs, an operation() that fails after a long Duration should not increments the backoff period.
+// If operation() takes more than MinJobInterval, Reset() is called in NextBackOff().
+type BackOff struct {
+	*backoff.ExponentialBackOff
+	MinJobInterval time.Duration
+}
+
+// NewBackOff creates an instance of BackOff using default values.
+func NewBackOff(backOff *backoff.ExponentialBackOff) *BackOff {
+	backOff.MaxElapsedTime = 0
+	return &BackOff{
+		ExponentialBackOff: backOff,
+		MinJobInterval:     defaultMinJobInterval,
+	}
+}
+
+// NextBackOff calculates the next backoff interval.
+func (b *BackOff) NextBackOff() time.Duration {
+	if b.GetElapsedTime() >= b.MinJobInterval {
+		b.Reset()
+	}
+	return b.ExponentialBackOff.NextBackOff()
+}