router/registry: add fallback if routes aren't found in the cache (#1758)

* router/registry: add fallback if routes aren't found in the cache

* router: fix rlock bug

* router/registry: pass fetchRoutes into the table, not the router

router/default.go

@@ -48,10 +48,13 @@ func newRouter(opts ...Option) Router {
 	// construct the router
 	r := &router{
 		options:     options,
-		table:       newTable(),
 		subscribers: make(map[string]chan *Advert),
 	}
 
+	// create the new table, passing the fetchRoute method in as a fallback if
+	// the table doesn't contain the result for a query.
+	r.table = newTable(r.fetchRoutes)
+
 	// start the router and return
 	r.start()
 	return r
@@ -176,6 +179,29 @@ func (r *router) manageRegistryRoutes(reg registry.Registry, action string) erro
 	return nil
 }
 
+// fetchRoutes retrieves all the routes for a given service and creates them in the routing table
+func (r *router) fetchRoutes(service string) error {
+	services, err := r.options.Registry.GetService(service, registry.GetDomain(registry.WildcardDomain))
+	if err != nil {
+		return fmt.Errorf("failed getting services: %v", err)
+	}
+
+	for _, srv := range services {
+		var domain string
+		if srv.Metadata != nil && len(srv.Metadata["domain"]) > 0 {
+			domain = srv.Metadata["domain"]
+		} else {
+			domain = registry.WildcardDomain
+		}
+
+		if err := r.manageRoutes(srv, "create", domain); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // watchRegistry watches registry and updates routing table based on the received events.
 // It returns error if either the registry watcher fails with error or if the routing table update fails.
 func (r *router) watchRegistry(w registry.Watcher) error {

router/table.go

@@ -19,6 +19,8 @@ var (
 // table is an in-memory routing table
 type table struct {
 	sync.RWMutex
+	// fetchRoutes for a service
+	fetchRoutes func(string) error
 	// routes stores service routes
 	routes map[string]map[uint64]Route
 	// watchers stores table watchers
@@ -26,10 +28,11 @@ type table struct {
 }
 
 // newtable creates a new routing table and returns it
-func newTable(opts ...Option) *table {
+func newTable(fetchRoutes func(string) error, opts ...Option) *table {
 	return &table{
-		routes:   make(map[string]map[uint64]Route),
-		watchers: make(map[string]*tableWatcher),
+		fetchRoutes: fetchRoutes,
+		routes:      make(map[string]map[uint64]Route),
+		watchers:    make(map[string]*tableWatcher),
 	}
 }
 
@@ -249,10 +252,23 @@ func (t *table) Query(q ...QueryOption) ([]Route, error) {
 	}
 
 	if opts.Service != "*" {
-		if _, ok := t.routes[opts.Service]; !ok {
-			return nil, ErrRouteNotFound
+		// try and load services from the cache
+		if _, ok := t.routes[opts.Service]; ok {
+			return findRoutes(t.routes[opts.Service], opts.Address, opts.Gateway, opts.Network, opts.Router, opts.Strategy), nil
 		}
-		return findRoutes(t.routes[opts.Service], opts.Address, opts.Gateway, opts.Network, opts.Router, opts.Strategy), nil
+
+		// load the cache and try again
+		t.RUnlock()
+		if err := t.fetchRoutes(opts.Service); err != nil {
+			return nil, err
+		}
+		t.RLock()
+		if _, ok := t.routes[opts.Service]; ok {
+			return findRoutes(t.routes[opts.Service], opts.Address, opts.Gateway, opts.Network, opts.Router, opts.Strategy), nil
+
+		}
+
+		return nil, ErrRouteNotFound
 	}
 
 	// search through all destinations

router/table_test.go

@@ -6,7 +6,8 @@ import (
 )
 
 func testSetup() (*table, Route) {
-	table := newTable()
+	router := newRouter().(*router)
+	table := router.table
 
 	route := Route{
 		Service: "dest.svc",