code: @Override
      public AttachInstancesResult attachInstances(AttachInstancesRequest request) {
          request = beforeClientExecution(request);
          return executeAttachInstances(request);
      }
docs: <p>
  Attaches one or more EC2 instances to the specified Auto Scaling group.
  </p>
  <p>
  When you attach instances, Amazon EC2 Auto Scaling increases the desired capacity of the group by the number of
  instances being attached. If the number of instances being attached plus the desired capacity of the group
  exceeds the maximum size of the group, the operation fails.
  </p>
  <p>
  If there is a Classic Load Balancer attached to your Auto Scaling group, the instances are also registered with
  the load balancer. If there are target groups attached to your Auto Scaling group, the instances are also
  registered with the target groups.
  </p>
  <p>
  For more information, see <a
  href="https://docs.aws.amazon.com/autoscaling/ec2/userguide/attach-instance-asg.html">Attach EC2 Instances to
  Your Auto Scaling Group</a> in the <i>Amazon EC2 Auto Scaling User Guide</i>.
  </p>
  
  @param attachInstancesRequest
  @return Result of the AttachInstances operation returned by the service.
  @throws ResourceContentionException
  You already have a pending update to an Amazon EC2 Auto Scaling resource (for example, an Auto Scaling
  group, instance, or load balancer).
  @throws ServiceLinkedRoleFailureException
  The service-linked role is not yet ready for use.
  @sample AmazonAutoScaling.AttachInstances
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/autoscaling-2011-01-01/AttachInstances" target="_top">AWS
  API Documentation</a>