fix: implement function to identify if node is present in aws

- this is a follow-up to kubernetes#5054
- this might fix kubernetes#4456

Signed-off-by: vadasambar <suraj.bankar@acquia.com>

fix: make `HasInstance` in aws provider thread-safe

Signed-off-by: vadasambar <suraj.bankar@acquia.com>
(cherry picked from commit 1cb55fe)

cluster-autoscaler/cloudprovider/aws/aws_cloud_provider.go

@@ -121,8 +121,19 @@ func (aws *awsCloudProvider) NodeGroupForNode(node *apiv1.Node) (cloudprovider.N
 }
 
 // HasInstance returns whether a given node has a corresponding instance in this cloud provider
-func (aws *awsCloudProvider) HasInstance(*apiv1.Node) (bool, error) {
-	return true, cloudprovider.ErrNotImplemented
+func (aws *awsCloudProvider) HasInstance(node *apiv1.Node) (bool, error) {
+	awsRef, err := AwsRefFromProviderId(node.Spec.ProviderID)
+	if err != nil {
+		return false, err
+	}
+
+	// we don't care about the status
+	status, err := aws.awsManager.asgCache.InstanceStatus(*awsRef)
+	if status != nil {
+		return true, nil
+	}
+
+	return false, fmt.Errorf("node is not present in aws: %v", err)
 }
 
 // Pricing returns pricing model for this cloud provider or error if not available.