BERT FineTuning with Cloud TPU: Sentence and Sentence-Pair Classification Tasks (TF 2.x)

This tutorial shows you how to train the Bidirectional Encoder Representations from Transformers (BERT) model on Cloud TPU.

BERT is a method of pre-training language representations. Pre-training refers to how BERT is first trained on a large source of text, such as Wikipedia. You can then apply the training results to other Natural Language Processing (NLP) tasks, such as question answering and sentiment analysis. With BERT and Cloud TPU, you can train a variety of NLP models in about 30 minutes.

For more information about BERT, see the following resources:

Objectives

Create a Cloud Storage bucket to hold your dataset and model output.
Run the training job.
Verify the output results.

Costs

This tutorial uses billable components of Google Cloud, including:

Compute Engine
Cloud TPU
Cloud Storage

Use the pricing calculator to generate a cost estimate based on your projected usage. New Google Cloud users might be eligible for a free trial.

Before you begin

This section provides information on setting up Cloud Storage bucket and a Compute Engine VM.

Open a Cloud Shell window.

Open Cloud Shell
Create a variable for your project's ID.
```
export PROJECT_ID=project-id
```
Configure gcloud command-line tool to use the project where you want to create Cloud TPU.
```
gcloud config set project ${PROJECT_ID}
```
The first time you run this command in a new Cloud Shell VM, an Authorize Cloud Shell page is displayed. Click Authorize at the bottom of the page to allow gcloud to make GCP API calls with your credentials.

Create a Service Account for the Cloud TPU project.

gcloud beta services identity create --service tpu.googleapis.com --project $PROJECT_ID

The command returns a Cloud TPU Service Account with following format:

service-PROJECT_NUMBER@cloud-tpu.iam.gserviceaccount.com

Create a Cloud Storage bucket using the following command:

Note: In the following command, replace bucket-name with the name you want to assign to your bucket.
```
gsutil mb -p ${PROJECT_ID} -c standard -l europe-west4 -b on gs://bucket-name
```
This Cloud Storage bucket stores the data you use to train your model and the training results. The gcloud compute tpus execution-groups command used in this tutorial sets up default permissions for the Cloud TPU Service Account you set up in the previous step. If you want finer-grain permissions, review the access level permissions.

The bucket location must be in the same region as your Compute Engine (VM) and your Cloud TPU node.
Launch a Compute Engine VM and Cloud TPU using the gcloud compute tpus execution-groups command.
```
$ gcloud compute tpus execution-groups create \
 --name=bert-tutorial \
 --zone=europe-west4-a \
 --tf-version=2.4.1 \
 --machine-type=n1-standard-1 \
 --accelerator-type=v3-8
```
Command flag descriptions

project

Your GCP project ID

name

The name of the Cloud TPU to create.

zone

The zone where you plan to create your Cloud TPU.

tf-version

The version of Tensorflow gcloud installs on the VM.

machine-type

The machine type of the Compute Engine VM to create.

accelerator-type

The type of the Cloud TPU to create.

For more information on the gcloud compute tpus execution-groups command, see the gcloud Reference.
When the gcloud command has finished executing, verify that your shell prompt has changed from username@projectname to username@vm-name. This change shows that you are now logged into your Compute Engine VM.

Note: If you are not connected to the Compute Engine instance, you can connect by running the following command:
```
gcloud compute ssh bert-tutorial --zone=europe-west4-a
```
As you continue these instructions, run each command that begins with (vm)$ in your VM session window.
Create an environment variable for the TPU name.
```
(vm)$ export TPU_NAME=bert-tutorial
```

Prepare the dataset

From your Compute Engine virtual machine (VM), install requirements.txt.

(vm)$ sudo pip3 install -r /usr/share/models/official/requirements.txt

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.

If you want to work with raw GLUE data and create TFRecords, follow the dataset processing instructions on GitHub.

Define parameter values

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

(vm)$ export STORAGE_BUCKET=gs://bucket-name

(vm)$ export PYTHONPATH="${PYTHONPATH}:/usr/share/models"
(vm)$ 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 /usr/share/models/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=1 \
  --model_dir=${MODEL_DIR} \
  --distribution_strategy=tpu \
  --tpu=${TPU_NAME} \
  --steps_per_loop=500

Command flag descriptions

mode: One of train, eval, train_and_eval, or predict.
input_meta_data_path: The path to a file that contains metadata about the dataset to be used for training and evaluation.
train_data_path: The Cloud Storage path for training input. It is set to the fake_imagenet dataset in this example.
eval_data_path: The Cloud Storage path for evaluation input. It is set to the fake_imagenet dataset in this example.
bert_config_file: The BERT configuration file.
init_checkpoint: The path to the json file containing the initial checkpoint of the pre-trained BERT model.
train_batch_size: The training batch size.
eval_batch_size: The evaluation batch size.
learning_rate: The learning rate.
num_train_epochs: The number of epochs to train the model.
model_dir: The Cloud Storage path where checkpoints and summaries are stored during model training. You can reuse an existing folder to load previously generated checkpoints and to store additional checkpoints as long as the previous checkpoints were created using a Cloud TPU of the same size and TensorFlow version.
distribution_strategy: To train the ResNet model on a TPU, set the distribution_strategy to tpu.
tpu: The name of the Cloud TPU to use for training.
steps_per_loop: The number of training steps to run before saving state to the CPU. A training step is the processing of one batch of examples. This includes both a forward pass and back propagation.

The training takes approximately 8 minutes on a v3-8 TPU. Upon completion the training script should display results like this:

12271/12271 [==============================]
  - 756s 62ms/step
  - loss: 0.4864
  - accuracy: 0.8055
  - val_loss: 0.3832
  - val_accuracy: 0.8546

To increase accuracy, set --num_tain_epochs=3. The script will take approximately one hour to train.

Clean up

Disconnect from the Compute Engine instance, if you have not already done so:
```
(vm)$ exit
```
Your prompt should now be username@projectname, showing you are in the Cloud Shell.
In your Cloud Shell, use the gcloud compute tpus execution-groups command shown below to delete your Compute Engine VM and the Cloud TPU. Use the --name and --zone flag values you used when you created the VM and TPU.
```
$ gcloud compute tpus execution-groups delete bert-tutorial \
  --zone=europe-west4-a
```
Verify the resources have been deleted by running gcloud compute tpus execution-groups list. The deletion might take several minutes. A response like the one below indicates your instances have been successfully deleted:
```
$ gcloud compute tpus execution-groups list \
  --zone=europe-west4-a
```
```
   NAME             STATUS
```
Delete your Cloud Storage bucket using gsutil as shown below. Replace bucket-name with the name of your Cloud Storage bucket.
```
$ gsutil rm -r gs://bucket-name
```

What's next

In this tutorial you have trained the BERT model using a sample dataset. The results of this training are (in most cases) not usable for inference. To use a model for inference you can train the data on a publicly available dataset or your own data set. Models trained on Cloud TPUs require datasets to be in TFRecord format.

You can use the dataset conversion tool sample to convert an image classification dataset into TFRecord format. If you are not using an image classification model, you will have to convert your dataset to TFRecord format yourself. For more information, see TFRecord and tf.Example

Hyperparameter tuning

To improve the model's performance with your dataset, you can tune the model's hyperparameters. You can find information about hyperparameters common to all TPU supported models on GitHub. Information about model-specific hyperparameters can be found in the source code for each model. For more information on hyperparameter tuning, see Overview of hyperparameter tuning, Using the Hyperparameter tuning service and Tune hyperparameters.

Inference

Once you have trained your model you can use it for inference (also called prediction). AI Platform is a cloud-based solution for developing, training, and deploying machine learning models. Once a model is deployed, you can use the AI Platform Prediction service.

Explore the TPU tools in TensorBoard.