consul: use the Near field instead of PreferLocal

command/agent/http.go

@@ -531,13 +531,7 @@ func (s *HTTPServer) parseToken(req *http.Request, token *string) {
 // DC in the request, if given, or else the agent's DC.
 func (s *HTTPServer) parseSource(req *http.Request, source *structs.QuerySource) {
 	s.parseDC(req, &source.Datacenter)
-	if node := req.URL.Query().Get("near"); node != "" {
-		if node == "_agent" {
-			source.Node = s.agent.config.NodeName
-		} else {
-			source.Node = node
-		}
-	}
+	source.Node = req.URL.Query().Get("near")
 }
 
 // parse is a convenience method for endpoints that need

command/agent/http_test.go

@@ -382,18 +382,6 @@ func TestParseSource(t *testing.T) {
 	if source.Datacenter != "foo" || source.Node != "bob" {
 		t.Fatalf("bad: %v", source)
 	}
-
-	// The magic "_agent" node name will use the agent's local node name.
-	req, err = http.NewRequest("GET",
-		"/v1/catalog/nodes?near=_agent", nil)
-	if err != nil {
-		t.Fatalf("err: %v", err)
-	}
-	source = structs.QuerySource{}
-	srv.parseSource(req, &source)
-	if source.Datacenter != "dc1" || source.Node != srv.agent.config.NodeName {
-		t.Fatalf("bad: %v", source)
-	}
 }
 
 func TestParseWait(t *testing.T) {

command/agent/prepared_query_endpoint_test.go

@@ -279,6 +279,7 @@ func TestPreparedQuery_Execute(t *testing.T) {
 
 		m.executeFn = func(args *structs.PreparedQueryExecuteRequest, reply *structs.PreparedQueryExecuteResponse) error {
 			expected := &structs.PreparedQueryExecuteRequest{
+				Origin:        srv.agent.config.NodeName,
 				Datacenter:    "dc1",
 				QueryIDOrName: "my-id",
 				Limit:         5,
@@ -350,6 +351,7 @@ func TestPreparedQuery_Explain(t *testing.T) {
 
 		m.explainFn = func(args *structs.PreparedQueryExecuteRequest, reply *structs.PreparedQueryExplainResponse) error {
 			expected := &structs.PreparedQueryExecuteRequest{
+				Origin:        srv.agent.config.NodeName,
 				Datacenter:    "dc1",
 				QueryIDOrName: "my-id",
 				Limit:         5,

consul/prepared_query_endpoint.go

@@ -368,12 +368,35 @@ func (p *PreparedQuery) Execute(args *structs.PreparedQueryExecuteRequest,
 	// Shuffle the results in case coordinates are not available if they
 	// requested an RTT sort.
 	reply.Nodes.Shuffle()
-	if err := p.srv.sortNodesByDistanceFrom(args.Source, reply.Nodes); err != nil {
+
+	// Get the source to sort by. This can be passed in by the requestor, or
+	// pre-defined using the Near parameter in the prepared query. If the
+	// near parameter was defined, that will be preferred.
+	sortFrom := args.Source
+	if query.Service.Near != "" {
+		sortFrom = structs.QuerySource{
+			Datacenter: args.Datacenter,
+			Node:       query.Service.Near,
+		}
+	}
+
+	// Respect the magic "_agent" flag.
+	preferLocal := false
+	if sortFrom.Node == "_agent" {
+		preferLocal = true
+		sortFrom.Node = args.Origin
+	}
+
+	// Perform the distance sort
+	if err := p.srv.sortNodesByDistanceFrom(sortFrom, reply.Nodes); err != nil {
 		return err
 	}
 
-	// Prefer the local service if it exists and is in the set.
-	if query.Service.PreferLocal {
+	// Nodes cannot be any "closer" than localhost, so this special case ensures
+	// the local node is returned first if it is present in the result. This
+	// allows the local agent to be preferred even when network coordinates are
+	// not enabled.
+	if preferLocal {
 		for i, node := range reply.Nodes {
 			if node.Node.Node == args.Origin {
 				remote := append(reply.Nodes[:i], reply.Nodes[i+1:]...)

consul/prepared_query_endpoint_test.go

@@ -1609,7 +1609,7 @@ func TestPreparedQuery_Execute(t *testing.T) {
 
 	// Set the query to prefer a colocated service
 	query.Op = structs.PreparedQueryUpdate
-	query.Query.Service.PreferLocal = true
+	query.Query.Service.Near = "_agent"
 	if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Apply", &query, &query.Query.ID); err != nil {
 		t.Fatalf("err: %v", err)
 	}
@@ -1630,7 +1630,6 @@ func TestPreparedQuery_Execute(t *testing.T) {
 			if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Execute", &req, &reply); err != nil {
 				t.Fatalf("err: %v", err)
 			}
-
 			if n := len(reply.Nodes); n != 10 {
 				t.Fatalf("expect 10 nodes, got: %d", n)
 			}
@@ -1640,8 +1639,27 @@ func TestPreparedQuery_Execute(t *testing.T) {
 		}
 	}
 
+	// Falls back to remote nodes if service is not available locally
+	{
+		req := structs.PreparedQueryExecuteRequest{
+			Origin:        "not-in-result",
+			Datacenter:    "dc1",
+			QueryIDOrName: query.Query.ID,
+			QueryOptions:  structs.QueryOptions{Token: execToken},
+		}
+
+		var reply structs.PreparedQueryExecuteResponse
+
+		if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Execute", &req, &reply); err != nil {
+			t.Fatalf("err: %v", err)
+		}
+		if n := len(reply.Nodes); n != 10 {
+			t.Fatalf("expect 10 nodes, got: %d", n)
+		}
+	}
+
 	// Remove local preference.
-	query.Query.Service.PreferLocal = false
+	query.Query.Service.Near = ""
 	if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Apply", &query, &query.Query.ID); err != nil {
 		t.Fatalf("err:% v", err)
 	}

consul/structs/prepared_query.go

@@ -34,10 +34,10 @@ type ServiceQuery struct {
 	// discarded)
 	OnlyPassing bool
 
-	// If PreferLocal is true, the local agent will be checked for a local
-	// copy of the service before continuing to remote machines. This is
-	// useful to prefer colocated services but fall back when unavailable.
-	PreferLocal bool
+	// Near allows the query to always prefer the node nearest the given
+	// node. If the node does not exist, results are returned in their
+	// normal randomly-shuffled order.
+	Near string
 
 	// Tags are a set of required and/or disallowed tags. If a tag is in
 	// this list it must be present. If the tag is preceded with "!" then
@@ -168,10 +168,6 @@ func (q *PreparedQuerySpecificRequest) RequestDatacenter() string {
 
 // PreparedQueryExecuteRequest is used to execute a prepared query.
 type PreparedQueryExecuteRequest struct {
-	// Origin is used to carry around a reference to the node which
-	// is executing the query on behalf of the client.
-	Origin string
-
 	// Datacenter is the target this request is intended for.
 	Datacenter string
 
@@ -182,6 +178,10 @@ type PreparedQueryExecuteRequest struct {
 	// Limit will trim the resulting list down to the given limit.
 	Limit int
 
+	// Origin is used to carry around a reference to the node which
+	// is executing the query on behalf of the client.
+	Origin string
+
 	// Source is used to sort the results relative to a given node using
 	// network coordinates.
 	Source QuerySource