# BERT FineTuning with Cloud TPU: Sentence and Sentence-Pair Classification Tasks (TF 2.1)
This tutorial shows you how to train the Bidirectional Encoder Representations from Transformers (BERT) model on Cloud TPU.


## Set up Cloud Storage and Compute Engine VM
1. [Open a cloud shell window](https://console.cloud.google.com/?cloudshell=true&_ga=2.11844148.-1612541229.1552429951)
2. Create a variable for the project's id:
```
export PROJECT_ID=your-project_id
```
3. Configure `gcloud` command-line tool to use the project where you want to create Cloud TPU.
```
gcloud config set project ${PROJECT_ID}
```
4. Create a Cloud Storage bucket using the following command:
```
gsutil mb -p ${PROJECT_ID} -c standard -l europe-west4 -b on gs://your-bucket-name
```
This Cloud Storage bucket stores the data you use to train your model and the training results.
5. Launch a Compute Engine VM and Cloud TPU using the ctpu up command.
```
ctpu up --tpu-size=v3-8 \
 --machine-type=n1-standard-8 \
 --zone=europe-west4-a \
 --tf-version=2.1 [optional flags: --project, --name]
```
6. The configuration you specified appears. Enter y to approve or n to cancel.
7. When the ctpu up command has finished executing, verify that your shell prompt has changed from username@project to username@tpuname. This change shows that you are now logged into your Compute Engine VM.
```
gcloud compute ssh vm-name --zone=europe-west4-a
(vm)$ export TPU_NAME=vm-name
```
As you continue these instructions, run each command that begins with `(vm)$` in your VM session window.

## Prepare the Dataset
1. From your Compute Engine virtual machine (VM), install requirements.txt.
```
(vm)$ cd /usr/share/models
(vm)$ sudo pip3 install -r official/requirements.txt
```
2. Optional: download download_glue_data.py

This tutorial uses the General Language Understanding Evaluation (GLUE) benchmark to evaluate and analyze the performance of the model. The GLUE data is provided for this tutorial at gs://cloud-tpu-checkpoints/bert/classification.

## Define parameter values
Next, define several parameter values that are required when you train and evaluate your model:

```
(vm)$ export PYTHONPATH="$PYTHONPATH:/usr/share/tpu/models"
(vm)$ export STORAGE_BUCKET=gs://your-bucket-name
(vm)$ export BERT_BASE_DIR=gs://cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16
(vm)$ export MODEL_DIR=${STORAGE_BUCKET}/bert-output
(vm)$ export GLUE_DIR=gs://cloud-tpu-checkpoints/bert/classification
(vm)$ export TASK=mnli
```

## Train the model
From your Compute Engine VM, run the following command.

```
(vm)$ python3 official/nlp/bert/run_classifier.py \
  --mode='train_and_eval' \
  --input_meta_data_path=${GLUE_DIR}/${TASK}_meta_data \
  --train_data_path=${GLUE_DIR}/${TASK}_train.tf_record \
  --eval_data_path=${GLUE_DIR}/${TASK}_eval.tf_record \
  --bert_config_file=$BERT_BASE_DIR/bert_config.json \
  --init_checkpoint=$BERT_BASE_DIR/bert_model.ckpt \
  --train_batch_size=32 \
  --eval_batch_size=32 \
  --learning_rate=2e-5 \
  --num_train_epochs=3 \
  --model_dir=${MODEL_DIR} \
  --distribution_strategy=tpu \
  --tpu=${TPU_NAME}
```

## Verify your results
The training takes approximately 1 hour on a v3-8 TPU. When script completes, you should see results similar to the following:
```
Training Summary:
{'train_loss': 0.28142181038856506,
'last_train_metrics': 0.9467429518699646,
'eval_metrics': 0.8599063158035278,
'total_training_steps': 36813}
```

## Clean up
To avoid incurring charges to your GCP account for the resources used in this topic:
1. Disconnect from the Compute Engine VM:
```
(vm)$ exit
```
2. In your Cloud Shell, run ctpu delete with the --zone flag you used when you set up the Cloud TPU to delete your Compute Engine VM and your Cloud TPU:
```
$ ctpu delete --zone=your-zone
```
3. Run ctpu status specifying your zone to make sure you have no instances allocated to avoid unnecessary charges for TPU usage. The deletion might take several minutes. A response like the one below indicates there are no more allocated instances:
```
$ ctpu status --zone=your-zone
```
4. Run gsutil as shown, replacing your-bucket with the name of the Cloud Storage bucket you created for this tutorial:
```
$ gsutil rm -r gs://your-bucket
```