"Failed to connect to remote host: Connection refused" on Colab TPU
Hi @davidkflau, Thank you for raising the issue!
We were able to replicate the issue in Colab using Tensorflow 2.12 and TPU. Please find the gist [here](https://colab.sandbox.google.com/gist/synandi/f1de44f03fd28314691b7d9ee3512600/60288_tpu.ipynb).  It seems like we have to dig deep into the issue. We'll update here soon. Thank you! Hi @davidkflau ,

At present not all Ops are executable with TPUs. The iter operation might be one of them. Also, from the error log:
```
Executing non-communication op <MultiDeviceIteratorGetNextFromShard> originally returned UnavailableError, and was replaced by InternalError to avoid invoking TF network error handling logic.
```

It seems iter operation is not supported on TPUs. Please find the TPU supported Ops list [here](https://cloud.google.com/tpu/docs/tensorflow-ops) for reference. 

Thank you! This issue is stale because it has been open for 7 days with no activity. It will be closed if no further activity occurs. Thank you. This issue was closed because it has been inactive for 7 days since being marked as stale. Please reopen if you'd like to work on this further. Are you satisfied with the resolution of your issue?
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<details><summary>Click to expand!</summary> 
 
 ### Issue Type

Bug

### Have you reproduced the bug with TF nightly?

No

### Source

source

### Tensorflow Version

tf 2.12.0

### Custom Code

Yes

### OS Platform and Distribution

_No response_

### Mobile device

_No response_

### Python version

_No response_

### Bazel version

_No response_

### GCC/Compiler version

_No response_

### CUDA/cuDNN version

_No response_

### GPU model and memory

_No response_

### Current Behaviour?

```shell
I got an error "Failed to connect to remote host: Connection refused" when I use TPU to train my model on Colab, but it works if I use GPU to train.
```


### Standalone code to reproduce the issue

```shell
My notebook is
https://colab.research.google.com/drive/1YUMZQe-z5cc9PAgGEch3xuEuloclNSRC?usp=sharing
```


### Relevant log output

```shell
Epoch 1/50
   1/1240 [..............................] - ETA: 10:24:26
---------------------------------------------------------------------------
InternalError                             Traceback (most recent call last)
<ipython-input-14-d0d9f97c5872> in <cell line: 2>()
      1 # Train the model
----> 2 history = model.fit(train_generator, validation_data=val_generator, epochs=50, verbose=1, shuffle=True)

1 frames
/usr/local/lib/python3.9/dist-packages/tensorflow/python/framework/ops.py in _numpy(self)
   1126       return self._numpy_internal()
   1127     except core._NotOkStatusException as e:  # pylint: disable=protected-access
-> 1128       raise core._status_to_exception(e) from None  # pylint: disable=protected-access
   1129 
   1130   @property

InternalError: 9 root error(s) found.
  (0) INTERNAL: {{function_node __inference_train_function_107490}} failed to connect to all addresses; last error: UNKNOWN: ipv4:127.0.0.1:50612: Failed to connect to remote host: Connection refused
Additional GRPC error information from remote target /job:localhost/replica:0/task:0/device:CPU:0:
:UNKNOWN:failed to connect to all addresses; last error: UNKNOWN: ipv4:127.0.0.1:50612: Failed to connect to remote host: Connection refused {created_time:"2023-04-11T06:57:27.796149613+00:00", grpc_status:14}
	 [[{{node MultiDeviceIteratorGetNextFromShard}}]]
Executing non-communication op <MultiDeviceIteratorGetNextFromShard> originally returned UnavailableError, and was replaced by InternalError to avoid invoking TF network error handling logic.
	 [[RemoteCall]]
	 [[IteratorGetNextAsOptional]]
	 [[strided_slice_91/_338]]
  (1) INTERNAL: {{function_node __inference_train_function_107490}} failed to connect to all addresses; last error: UNKNOWN: ipv4:127.0.0.1:50612: Failed to connect to remote host: Connection refused
Additional GRPC error information from remote target /job:localhost/replica:0/task:0/device:CPU:0:
:UNKNOWN:failed to connect to all addresses; last error: UNKNOWN: ipv4:127.0.0.1:50612: Failed to connect to remote host: Connection refused {created_time:"2023-04-11T06:57:27.796149613+00:00", grpc_status:14}
	 [[{{node MultiDeviceIteratorGetNextFromShard}}]]
Executing non-communication op <MultiDeviceIteratorGetNextFromShard> originally returned UnavailableError, and was replaced by InternalError to avoid invoking TF network error handling logic.
	 [[RemoteCall]]
	 [[IteratorGetNextAsOptional]]
	 [[strided_slice_72/_312]]
  (2) INTERNAL: {{function_node __inference_train_function_107490}} failed to connect to all addresses; last error: UNKNOWN: ipv4:127.0.0.1:50612: Failed to connect to remote host: Connection refused
Additional GRPC error information from remote target /job:localhost/replica:0/task:0/device:CPU:0:
:UNKNOWN:failed to connect to all addresses; last error: UNKNOWN: ipv4:127.0.0.1:50612: Failed to connect to remote host: Connection refused {created_time:"2023-04-11T06:57:27.796149613+00:00", grpc_status:14}
	 [[{{node MultiDeviceIteratorGetNextFromShard}}]]
Executing non-communication op <MultiDeviceIteratorGetNextFromShard> originally returned UnavailableError, and was replaced by InternalError to avoid invoking TF network error handling logic.
	 [[RemoteCall]]
	 [[IteratorGetNextAsOptional]]
	 [[strided_slice_37/_266]]
  (3) INTERNAL: {{function_node __inference_train_function_107490}} failed to connect to all addresses; last error: UNKNOWN: ipv4:127.0.0.1:50612: Failed to connect to remote host: Connection refused
Additional GRPC error information from remote target /job:localhost/replica:0/task:0/device:CPU:0:
:UNKNOWN:failed to connect to all addresses; last error: UNKNOWN: ipv4:127.0.0.1:50612: Failed to connect to remote host: Connection refused {created_time:"2023-04-11T06:57:27.796149613+00:00", grpc_status:14}
	 [[{{node MultiDeviceIteratorGetNextFromShard}}]]
Ex ... [truncated]
```
</details>