%instance_key = "tf.Const"() { value = dense<3> : tensor<i32> } : () -> tensor<i32>
  // CHECK: %[[REDUCE:.*]] = "mhlo.all_reduce"
  // CHECK-SAME{LITERAL}: replica_groups = dense<[[0, 1]]> : tensor<1x2xi64>
  // CHECK: mhlo.add
  // CHECK: mhlo.return
  // CHECK: return %[[REDUCE]]

  Pattern<
    (TF_CollectiveReduceV2Op:$src_op
       $input, $group_size, $group_key, $instance_key, $ordering_token,
       $merge_op, $final_op, $communication_hint, $timeout_seconds,
       $is_stateless, $max_subdivs_per_device
    ),
    [(TF_CollectiveReduceV2Op
       $input, $group_size, $group_key, $instance_key, (EmptyList),
       $merge_op, $final_op, $communication_hint, $timeout_seconds,

  TFE_OpSetAttrType(op.get(), "T", TFE_TensorHandleDataType(input));
  TFE_OpSetAttrInt(op.get(), "group_size", group_size);
  TFE_OpSetAttrInt(op.get(), "group_key", 0);
  TFE_OpSetAttrInt(op.get(), "instance_key", 0);
  const std::string merge_op("Add");
  TFE_OpSetAttrString(op.get(), "merge_op", merge_op.c_str(),
                      merge_op.length());
  const std::string final_op("Id");

          {{"y"},
           "CollectiveReduce",
           {"x"},
           {{"T", DT_FLOAT},
            {"group_size", static_cast<int>(devices.size())},
            {"group_key", 0},
            {"instance_key", 0},
            {"merge_op", "Add"},
            {"final_op", "Id"},
            {"subdiv_offsets", std::vector<int>()}},
           /*dep=*/{"assert"}},
      });

  TF_DeleteStatus(status);

  TFE_OpSetAttrType(op, "T", TFE_TensorHandleDataType(in));
  TFE_OpSetAttrInt(op, "group_size", group_size);
  TFE_OpSetAttrInt(op, "group_key", 123);
  TFE_OpSetAttrInt(op, "instance_key", 456);
  TFE_OpSetAttrString(op, "merge_op", "Add", 3);
  TFE_OpSetAttrString(op, "final_op", "Id", 2);
  std::vector<int64_t> subdiv_offsets;
  TFE_OpSetAttrIntList(op, "subdiv_offsets", subdiv_offsets.data(),

)

// instancesKey acts as a key to identify all instances for a given hostname/namespace pair
// This is mostly used as an index
type instancesKey struct {
	hostname  host.Name
	namespace string
}

type octetPair struct {
	thirdOctet  int
	fourthOctet int
}

func makeInstanceKey(i *model.ServiceInstance) instancesKey {
	return instancesKey{i.Service.Hostname, i.Service.Attributes.Namespace}

	}
	expected := map[string]struct{}{}
	for _, i := range want {
		expected[instanceKey(i)] = struct{}{}
	}
	unexpected := map[string]struct{}{}
	for _, i := range all {
		k := instanceKey(i)
		if _, ok := expected[k]; !ok {
			unexpected[k] = struct{}{}
		}
	}
	for _, i := range got {
		k := instanceKey(i)
		// just remove the items rather than looping over expected, if anythings left we missed it