Don't attempt to destroy services scaled > 0

This led to an unfortunate situation where the target group was
destroyed by the service was not which broke all manner of things.

CHANGELOG.md

@@ -6,9 +6,10 @@
 - service create and task run will no longer create a repository if an image is
   explictly passed.
 - service destroy will remove all references the service's target group and
-  delete it
+  delete it.
 - Fix git repo detection to properly use a git sha image tag rather than a
-  time stamp tag ([#6][issue-6])
+  time stamp tag. ([#6][issue-6])
+- Fail fast if a user attempts to destroy a service scaled above 0.
 
 ## 0.2.0 (2017-12-31)
 

cmd/service_destroy.go

@@ -38,6 +38,11 @@ func destroyService(operation *ServiceDestroyOperation) {
 	ecs := ECS.New(sess, clusterName)
 	service := ecs.DescribeService(operation.ServiceName)
 
+	if service.DesiredCount > 0 {
+		err := fmt.Errorf("%d tasks running, scale service to 0", service.DesiredCount)
+		console.ErrorExit(err, "Cannot destroy service %s", operation.ServiceName)
+	}
+
 	if service.TargetGroupArn != "" {
 		loadBalancerArn := elbv2.GetTargetGroupLoadBalancerArn(service.TargetGroupArn)
 		loadBalancer := elbv2.DescribeLoadBalancerByArn(loadBalancerArn)