Refactor: Change Fetch signature

Have the source Fetch functionality return a map of instances
instead of a slice. The metric collection functionality writes
to a map, so using a slice was adding an extra loop in order
to return the correct type.

Author: gabibeyer

pkg/plugin/example/source/example.go

@@ -25,10 +25,10 @@ type ExampleSource struct {
 // Fetch is what gets run by aether, it should return a list of instances with
 // the metrics attached to them (CPU, Memory, Networking, Storage)
 // Your business logic should be handeled here
-func (e *ExampleSource) Fetch(ctx context.Context) ([]*v1.Instance, error) {
+func (e *ExampleSource) Fetch(ctx context.Context) (map[string]*v1.Instance, error) {
 	// business logic here
-	return []*v1.Instance{
-		{
+	return map[string]*v1.Instance{
+		"example": {
 			ID:       "123456789",
 			Provider: v1.Custom,
 			Service:  "On-Prem",

pkg/providers/aws/source.go

@@ -47,7 +47,7 @@ func Sources(ctx context.Context, cfg *config.Provider) []v1.Source {
 
 // Fetch returns a slice of instances, this is to adhere to the sources
 // interface
-func (s *Source) Fetch(ctx context.Context) ([]*v1.Instance, error) {
+func (s *Source) Fetch(ctx context.Context) (map[string]*v1.Instance, error) {
 	if s.Region == "" {
 		return nil, errors.New("no region set")
 	}
@@ -64,12 +64,7 @@ func (s *Source) Fetch(ctx context.Context) ([]*v1.Instance, error) {
 		return nil, fmt.Errorf("failed getting instance metrics: %v", err)
 	}
 
-	var instances []*v1.Instance
-	for _, instance := range s.Client.instancesMap {
-		instances = append(instances, instance)
-	}
-
-	return instances, nil
+	return s.Client.instancesMap, nil
 }
 
 // Stop is used to gracefully shutdown a source

pkg/providers/gcp/source.go

@@ -49,7 +49,7 @@ func Sources(ctx context.Context, cfg *config.Provider) []v1.Source {
 
 // Fetch returns a slice of instances, this is to adhere to the sources
 // interface
-func (s *Source) Fetch(ctx context.Context) ([]*v1.Instance, error) {
+func (s *Source) Fetch(ctx context.Context) (map[string]*v1.Instance, error) {
 	if s.Project == nil {
 		return nil, errors.New("no project set")
 	}
@@ -66,18 +66,15 @@ func (s *Source) Fetch(ctx context.Context) ([]*v1.Instance, error) {
 		return nil, fmt.Errorf("failed getting instance metrics: %v", err)
 	}
 
-	var instances []*v1.Instance
 	for k, instance := range s.Client.instancesMap {
-		instances = append(instances, instance)
-
 		// remove terminated instances as we
 		// shouldnt use them anymore
 		if instance.Status == v1.InstanceTerminated {
 			delete(s.Client.instancesMap, k)
 		}
 	}
 
-	return instances, nil
+	return s.Client.instancesMap, nil
 }
 
 // Stop is used to gracefully shutdown a source

pkg/source/manager.go

@@ -105,11 +105,11 @@ func (m *Manager) Fetch(ctx context.Context) {
 
 // publishInstances is a helper that publishes each instance in a slice on the
 // bus under the MetricsCollectedEvent
-func (m *Manager) publishInstances(instances []*v1.Instance) error {
-	for i := range instances {
+func (m *Manager) publishInstances(instances map[string]*v1.Instance) error {
+	for _, i := range instances {
 		err := m.bus.Publish(&bus.Event{
 			Type: v1.MetricsCollectedEvent,
-			Data: *instances[i],
+			Data: *i,
 		})
 		if err != nil {
 			return err

pkg/types/v1/source.go

@@ -7,7 +7,8 @@ type Source interface {
 	// Stop is the "teardown" that will be used for graceful shutdown
 	Stop(context.Context) error
 
-	// Fetch is the business logic that should return a list of instances
-	// that have metrics attached to them mainly cpu, memory, storage and network
-	Fetch(context.Context) ([]*Instance, error)
+	// Fetch is the business logic that should return a map of instances
+	// with a unique instanceID key, and value of instance that have
+	// metrics attached to them mainly cpu, memory, storage and network
+	Fetch(context.Context) (map[string]*Instance, error)
 }