Add debug logs

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -438,6 +438,7 @@ func (h *Handler) proxyLoopIteration(r *http.Request, w http.ResponseWriter, pro
 			for _, dUp := range dUpstreams {
 				h.provisionUpstream(dUp)
 			}
+			h.logger.Debug("provisioned dynamic upstreams", zap.Int("count", len(dUpstreams)))
 			defer func() {
 				// these upstreams are dynamic, so they are only used for this iteration
 				// of the proxy loop; be sure to let them go away when we're done with them
@@ -468,6 +469,10 @@ func (h *Handler) proxyLoopIteration(r *http.Request, w http.ResponseWriter, pro
 		return true, fmt.Errorf("making dial info: %v", err)
 	}
 
+	h.logger.Debug("selected upstream",
+		zap.String("dial", dialInfo.Address),
+		zap.Int("total_upstreams", len(upstreams)))
+
 	// attach to the request information about how to dial the upstream;
 	// this is necessary because the information cannot be sufficiently
 	// or satisfactorily represented in a URL

modules/caddyhttp/reverseproxy/upstreams.go

@@ -137,6 +137,11 @@ func (su SRVUpstreams) GetUpstreams(r *http.Request) ([]*Upstream, error) {
 	proto := repl.ReplaceAll(su.Proto, "")
 	name := repl.ReplaceAll(su.Name, "")
 
+	su.logger.Debug("refreshing SRV upstreams",
+		zap.String("service", service),
+		zap.String("proto", proto),
+		zap.String("name", name))
+
 	_, records, err := su.resolver.LookupSRV(r.Context(), service, proto, name)
 	if err != nil {
 		// From LookupSRV docs: "If the response contains invalid names, those records are filtered
@@ -150,9 +155,13 @@ func (su SRVUpstreams) GetUpstreams(r *http.Request) ([]*Upstream, error) {
 
 	upstreams := make([]*Upstream, len(records))
 	for i, rec := range records {
-		upstreams[i] = &Upstream{
-			Dial: net.JoinHostPort(rec.Target, strconv.Itoa(int(rec.Port))),
-		}
+		su.logger.Debug("discovered SRV record",
+			zap.String("target", rec.Target),
+			zap.Uint16("port", rec.Port),
+			zap.Uint16("priority", rec.Priority),
+			zap.Uint16("weight", rec.Weight))
+		addr := net.JoinHostPort(rec.Target, strconv.Itoa(int(rec.Port)))
+		upstreams[i] = &Upstream{Dial: addr}
 	}
 
 	// before adding a new one to the cache (as opposed to replacing stale one), make room if cache is full