add healthcheck service

internal/probe/readiness.go

@@ -0,0 +1,30 @@
+package probe
+
+// Readiness reports compoent's readiness.
+type Readiness int8
+
+const (
+	// ReadinessUnknown means rediness was unset.
+	ReadinessUnknown Readiness = iota
+	// ReadinessNotReady reports provided component is not ready.
+	ReadinessNotReady
+	// ReadinessFailed reports there were a problem with component.
+	ReadinessFailed
+	// ReadinessOk reports the component is ready to work.
+	ReadinessOk
+)
+
+type ReadinessAggregate []Readiness
+
+func (a ReadinessAggregate) Status() Readiness {
+	for _, item := range a {
+		switch item {
+		case ReadinessOk, ReadinessUnknown:
+			continue
+		}
+
+		return item
+	}
+
+	return ReadinessOk
+}