mw/etcd: fix 'fallthrough' (#1026)

* mw/etcd: revert 'add fallthrough'

This removes 'fallthrough' for *etcd* which is not needed. This was
added in 00f5c779 but is totally not needed and creates backwards
incompat behavior even.

Thanks to @johnbelamaric for pointing this out in #925.

* remove here as well

* Revert "remove here as well"

This reverts commit 9d44397827425e567af01d43564c4294b42e98c9.

* Revert "mw/etcd: revert 'add fallthrough'"

This reverts commit 0cfe3cb1ab5495ed38a8a0486e3f5386f3bd95dc.

* mw/{etcd,kubernetes}: use fallthrough correctly

reverts of reverts, will rebase and squash later.

middleware/etcd/handler.go

@@ -42,10 +42,7 @@ func (e *Etcd) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
 		if opt.Debug != "" {
 			r.Question[0].Name = opt.Debug
 		}
-		if e.Fallthrough {
-			return middleware.NextOrFailure(e.Name(), e.Next, ctx, w, r)
-		}
-		return dns.RcodeServerFailure, nil
+		return middleware.NextOrFailure(e.Name(), e.Next, ctx, w, r)
 	}
 
 	var (
@@ -88,6 +85,9 @@ func (e *Etcd) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
 	}
 
 	if e.IsNameError(err) {
+		if e.Fallthrough {
+			return middleware.NextOrFailure(e.Name(), e.Next, ctx, w, r)
+		}
 		// Make err nil when returning here, so we don't log spam for NXDOMAIN.
 		return middleware.BackendError(e, zone, dns.RcodeNameError, state, debug, nil /* err */, opt)
 	}

middleware/kubernetes/handler.go

@@ -19,10 +19,7 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 
 	zone := middleware.Zones(k.Zones).Matches(state.Name())
 	if zone == "" {
-		if k.Fallthrough {
-			return middleware.NextOrFailure(k.Name(), k.Next, ctx, w, r)
-		}
-		return dns.RcodeServerFailure, nil
+		return middleware.NextOrFailure(k.Name(), k.Next, ctx, w, r)
 	}
 
 	state.Zone = zone