PyTorch Lightning API#

In this guide, you’ll learn how to use the PyTorch Lightning API.

Visit the API reference

det.pytorch.lightning API Reference

This document guides you through training a PyTorch Lightning model in Determined. You need to implement a trial class that inherits LightningAdapter and specify it as the entrypoint in the experiment configuration.

PyTorch Lightning Adapter, defined here as LightningAdapter, provides a quick way to train your PyTorch Lightning models with all the Determined features, such as mid-epoch preemption, easy distributed training, simple job submission to the Determined cluster, and so on.

LightningAdapter is built on top of our PyTorch API, which has a built-in training loop that integrates with the Determined features. However, it only supports LightningModule (v1.2.0). To migrate your code from the Trainer, please read more about PyTorch API and Experiment Configuration Reference.

Port PyTorch Lightning Code#

Porting your PyTorchLightning code is often pretty simple:

  1. Bring in your LightningModule and LightningDataModule and initialize them

  2. Create a new trial based on LightningAdapter and initialize it.

  3. Define the dataloaders.

Here is an example:

from determined.pytorch import PyTorchTrialContext, DataLoader
from determined.pytorch.lightning import LightningAdapter

# bring in your LightningModule and optionally LightningDataModule
from mnist import LightningMNISTClassifier, MNISTDataModule

class MNISTTrial(LightningAdapter):
    def __init__(self, context: PyTorchTrialContext) -> None:
        # instantiate your LightningModule with hyperparameter from the Determined
        # config file or from the searcher for automatic hyperparameter tuning.
        lm = LightningMNISTClassifier(lr=context.get_hparam("learning_rate"))

        # instantiate your LightningDataModule and make it distributed training ready.
        data_dir = f"/tmp/data-rank{context.distributed.get_rank()}" = MNISTDataModule(context.get_data_config()["url"], data_dir)

        # initialize LightningAdapter.
        super().__init__(context, lightning_module=lm)

    def build_training_data_loader(self) -> DataLoader:
        dl =
        return DataLoader(
            dl.dataset, batch_size=dl.batch_size, num_workers=dl.num_workers

    def build_validation_data_loader(self) -> DataLoader:
        dl =
        return DataLoader(
            dl.dataset, batch_size=dl.batch_size, num_workers=dl.num_workers

In this approach, the LightningModule is not paired with the PyTorch Lightning Trainer so that there are some methods and hooks that are not supported. Read about those here:

  • No separate test-set definition in Determined: test_step, test_step_end, test_epoch_end, on_test_batch_start, on_test_batch_end, on_test_epoch_start, on_test_epoch_end, test_dataloader.

  • No fit or pre-train stage: setup, teardown, on_fit_start, on_fit_end, on_pretrain_routine_start, on_pretrain_routine_end.

  • Additionally, no: training_step_end & validation_step_end, hiddens parameter in training_step and tbptt_split_batch, transfer_batch_to_device, get_progress_bar_dict, on_train_epoch_end, manual_backward, backward, optimizer_step, optimizer_zero_grad

In addition, we also patched some LightningModule methods to make porting your code easier:

  • log and log_dict are patched to always ship their values to TensorBoard. In the current version only the first two arguments in log: key and value, and the first argument in log_dict are supported.


Make sure to return the metric you defined as searcher.metric in your experiment’s configuration from your validation_step.


Determined will automatically log the metrics you return from training_step and validation_step to TensorBoard.


Determined environment images no longer contain PyTorch Lightning. To use PyTorch Lightning, add a line similar to the following in the script:

pip install pytorch_lightning==1.5.10 torchmetrics==0.5.1

To learn about this API, start by reading the trial definitions from the following examples:

Load Data#


Before loading data, read this document Prepare Data to understand how to work with different sources of data.

Loading your dataset when using PyTorch Lightning works the same way as it does with PyTorch API.

If you already have a LightningDataModule you can bring it in and use it to implement build_training_data_loader and build_validation_data_loader methods easily. For more information read PyTorchTrial’s section on Data Loading.