add registry base interface, mdns, noop implementations, add resolver, client

utils/backoff/backoff.go

@@ -0,0 +1,16 @@
+// Package backoff provides backoff functionality
+package backoff
+
+import (
+	"math"
+	"time"
+)
+
+// Do is a function x^e multiplied by a factor of 0.1 second.
+// Result is limited to 2 minute.
+func Do(attempts int) time.Duration {
+	if attempts > 13 {
+		return 2 * time.Minute
+	}
+	return time.Duration(math.Pow(float64(attempts), math.E)) * time.Millisecond * 100
+}