code: @BetaApi
    public final Operation removeInstancesInstanceGroup(
        ProjectZoneInstanceGroupName instanceGroup,
        InstanceGroupsRemoveInstancesRequest instanceGroupsRemoveInstancesRequestResource) {
  
      RemoveInstancesInstanceGroupHttpRequest request =
          RemoveInstancesInstanceGroupHttpRequest.newBuilder()
              .setInstanceGroup(instanceGroup == null ? null : instanceGroup.toString())
              .setInstanceGroupsRemoveInstancesRequestResource(
                  instanceGroupsRemoveInstancesRequestResource)
              .build();
      return removeInstancesInstanceGroup(request);
    }
docs: Removes one or more instances from the specified instance group, but does not delete those
  instances.
  
  <p>If the group is part of a backend service that has enabled connection draining, it can take
  up to 60 seconds after the connection draining duration before the VM instance is removed or
  deleted.
  
  <p>Sample code:
  
  <pre><code>
  try (InstanceGroupClient instanceGroupClient = InstanceGroupClient.create()) {
  ProjectZoneInstanceGroupName instanceGroup = ProjectZoneInstanceGroupName.of("[PROJECT]", "[ZONE]", "[INSTANCE_GROUP]");
  InstanceGroupsRemoveInstancesRequest instanceGroupsRemoveInstancesRequestResource = InstanceGroupsRemoveInstancesRequest.newBuilder().build();
  Operation response = instanceGroupClient.removeInstancesInstanceGroup(instanceGroup, instanceGroupsRemoveInstancesRequestResource);
  }
  </code></pre>
  
  @param instanceGroup The name of the instance group where the specified instances will be
  removed.
  @param instanceGroupsRemoveInstancesRequestResource
  @throws com.google.api.gax.rpc.ApiException if the remote call fails