Use weights from xDS

use the weights as reported. Set prio to 0 to signal it's not used.
Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/traffic/README.md

@@ -108,7 +108,7 @@ For SRV queries all endpoints are returned, the SRV target names are synthesized
 
 ## Matching Algorithm
 
-How are clients match against the data we receive from xDS endpoint?
+How are queries match against the data we receive from xDS endpoint?
 
 1.  Does the cluster exist? If not return NXDOMAIN, otherwise continue.
 
@@ -116,7 +116,9 @@ How are clients match against the data we receive from xDS endpoint?
     endpoint return a NODATA response, otherwise continue.
 
 3.  If weights are assigned, use those to pick an endpoint, otherwise randomly pick one and return a
-    response to the client.
+    response to the client. Weights are copied from the xDS data, priority is not used and set to 0
+    for all SRV records. Note that weights in SRV records are 16 bits, but xDS uses uint32; you have
+    been warned.
 
 ## Metrics
 

plugin/traffic/traffic.go

@@ -103,7 +103,7 @@ func (t *Traffic) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
 		}
 		m.Answer = []dns.RR{&dns.AAAA{Hdr: dns.RR_Header{Name: state.QName(), Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: 5}, AAAA: sockaddr.Address()}}
 	case dns.TypeSRV:
-		sockaddrs, _ := t.c.All(cluster, true)
+		sockaddrs, weights, _ := t.c.All(cluster, true)
 		m.Answer = make([]dns.RR, 0, len(sockaddrs))
 		m.Extra = make([]dns.RR, 0, len(sockaddrs))
 		for i, sa := range sockaddrs {
@@ -111,7 +111,7 @@ func (t *Traffic) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
 
 			m.Answer = append(m.Answer, &dns.SRV{
 				Hdr:      dns.RR_Header{Name: state.QName(), Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: 5},
-				Priority: 100, Weight: 100, Port: sa.Port(), Target: target})
+				Priority: 0, Weight: uint16(weights[i]), Port: sa.Port(), Target: target})
 
 			if sa.Address().To4() == nil {
 				m.Extra = append(m.Extra, &dns.AAAA{Hdr: dns.RR_Header{Name: target, Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: 5}, AAAA: sa.Address()})
@@ -120,7 +120,7 @@ func (t *Traffic) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
 			}
 		}
 	case dns.TypeTXT:
-		sockaddrs, _ := t.c.All(cluster, false)
+		sockaddrs, weights, _ := t.c.All(cluster, false)
 		m.Answer = make([]dns.RR, 0, len(sockaddrs))
 		m.Extra = make([]dns.RR, 0, len(sockaddrs))
 		for i, sa := range sockaddrs {
@@ -128,7 +128,7 @@ func (t *Traffic) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
 
 			m.Answer = append(m.Answer, &dns.TXT{
 				Hdr: dns.RR_Header{Name: state.QName(), Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: 5},
-				Txt: []string{"100", "100", strconv.Itoa(int(sa.Port())), target, corepb2.HealthStatus_name[int32(sa.Health)]}})
+				Txt: []string{"0", strconv.Itoa(int(uint16(weights[i]))), strconv.Itoa(int(sa.Port())), target, corepb2.HealthStatus_name[int32(sa.Health)]}})
 			m.Extra = append(m.Extra, &dns.TXT{Hdr: dns.RR_Header{Name: target, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: 5}, Txt: []string{sa.Address().String()}})
 		}
 	default:
@@ -162,7 +162,7 @@ func (t *Traffic) serveEndpoint(ctx context.Context, state request.Request, endp
 		return 0, nil
 	}
 
-	sockaddrs, _ := t.c.All(cluster, healthy)
+	sockaddrs, _, _ := t.c.All(cluster, healthy)
 	if len(sockaddrs) < nr {
 		m.Ns = soa(state.Zone)
 		m.Rcode = dns.RcodeNameError

plugin/traffic/xds/assignment.go

@@ -126,21 +126,27 @@ func (a *assignment) Select(cluster string, healthy bool) (*SocketAddress, bool)
 	return nil, true
 }
 
-// All returns all healthy endpoints.
-func (a *assignment) All(cluster string, healthy bool) ([]*SocketAddress, bool) {
+// All returns all healthy endpoints, together with their weights.
+func (a *assignment) All(cluster string, healthy bool) ([]*SocketAddress, []uint32, bool) {
 	cla := a.ClusterLoadAssignment(cluster)
 	if cla == nil {
-		return nil, false
+		return nil, nil, false
 	}
 
 	sa := []*SocketAddress{}
+	we := []uint32{}
 	for _, ep := range cla.Endpoints {
 		for _, lb := range ep.GetLbEndpoints() {
 			if healthy && lb.GetHealthStatus() != corepb2.HealthStatus_HEALTHY {
 				continue
 			}
+			weight := lb.GetLoadBalancingWeight().GetValue()
+			if weight > 2^16 {
+				log.Warning("Weight in cluster %q > %d, truncating to %d in SRV responses", cluster, weight, uint16(weight))
+			}
+			we = append(we, weight)
 			sa = append(sa, &SocketAddress{lb.GetEndpoint().GetAddress().GetSocketAddress(), lb.GetHealthStatus()})
 		}
 	}
-	return sa, true
+	return sa, we, true
 }

plugin/traffic/xds/client.go

@@ -205,9 +205,9 @@ func (c *Client) Select(cluster string, healty bool) (*SocketAddress, bool) {
 }
 
 // All returns all endpoints.
-func (c *Client) All(cluster string, healty bool) ([]*SocketAddress, bool) {
+func (c *Client) All(cluster string, healty bool) ([]*SocketAddress, []uint32, bool) {
 	if cluster == "" {
-		return nil, false
+		return nil, nil, false
 	}
 	return c.assignments.All(cluster, healty)
 }