Change cache policy

agent/service_mapper.go

@@ -67,7 +67,7 @@ func (s *ServiceMapper) update(metadata model.ServicesMetadata) {
 	var changes model.ServicesMetadata
 
 	for k, v := range metadata {
-		if _, ok := s.cache[k]; ok {
+		if !s.shouldAdd(k, metadata) {
 			continue
 		}
 
@@ -87,3 +87,22 @@ func (s *ServiceMapper) update(metadata model.ServicesMetadata) {
 	s.out <- changes
 	s.cache.Merge(changes)
 }
+
+func (s *ServiceMapper) shouldAdd(service string, metadata model.ServicesMetadata) bool {
+	cacheEntry, ok := s.cache[service]
+
+	// No cache entry?
+	if !ok {
+		return true
+	}
+
+	// Cache entry came from service API?
+	if _, ok = cacheEntry[model.ServiceApp]; ok {
+		return false
+	}
+
+	// New metadata value came from service API?
+	_, ok = metadata[service][model.ServiceApp]
+
+	return ok
+}

agent/service_mapper_test.go

@@ -38,6 +38,36 @@ func TestServiceMapper(t *testing.T) {
 	assert.Len(mapper.cache, 2)
 }
 
+func TestCachePolicy(t *testing.T) {
+	assert := assert.New(t)
+
+	mapper, in, out := testMapper()
+	mapper.Start()
+	defer mapper.Stop()
+
+	input := model.ServicesMetadata{"service-a": {"app_type": "type-a"}}
+	in <- input
+	output := <-out
+
+	// A new service entry should propagate the metadata the the outbound channel
+	assert.Equal(input, output)
+
+	// A service entry that is already in cache should only be propagated IF:
+	// - Current version does NOT have "app"
+	// - New version DOES have "app"
+
+	// This first attempt won't be propagated to the writer
+	firstAttempt := model.ServicesMetadata{"service-a": {"app_type": "FIRST_ATTEMPT"}}
+	in <- firstAttempt
+
+	// But this second will
+	secondAttempt := model.ServicesMetadata{"service-a": {"app_type": "SECOND_ATTEMPT", "app": "app-a"}}
+	in <- secondAttempt
+
+	output = <-out
+	assert.Equal(secondAttempt, output)
+}
+
 func testMapper() (mapper *ServiceMapper, in, out chan model.ServicesMetadata) {
 	in = make(chan model.ServicesMetadata, 1)
 	out = make(chan model.ServicesMetadata, 1)

model/services.go

@@ -14,6 +14,9 @@ type ServicesMetadata map[string]map[string]string
 // AppType is one of the pieces of information embedded in ServiceMetadata
 const AppType = "app_type"
 
+// ServiceApp represents the app to which certain integration belongs to
+const ServiceApp = "app"
+
 // Merge adds all entries from s2 to s1
 func (s1 ServicesMetadata) Merge(s2 ServicesMetadata) {
 	for k, v := range s2 {