Add a no-operation router

To be used for Kubernetes blue/green deployments (no service mesh or ingress controller)

pkg/router/nop.go

@@ -0,0 +1,24 @@
+package router
+
+import (
+	flaggerv1 "github.com/weaveworks/flagger/pkg/apis/flagger/v1alpha3"
+)
+
+// NopRouter no-operation router
+type NopRouter struct {
+}
+
+func (*NopRouter) Reconcile(canary *flaggerv1.Canary) error {
+	return nil
+}
+
+func (*NopRouter) SetRoutes(canary *flaggerv1.Canary, primaryWeight int, canaryWeight int) error {
+	return nil
+}
+
+func (*NopRouter) GetRoutes(canary *flaggerv1.Canary) (primaryWeight int, canaryWeight int, err error) {
+	if canary.Status.Iterations > 0 {
+		return 0, 100, nil
+	}
+	return 100, 0, nil
+}