Scale PyTorch Applications

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Run in Google Colab  View source on GitHub

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In this guide we will describe how to scale out PyTorch programs using Orca in 5 simple steps.

Step 0: Prepare Environment

We recommend using conda to prepare the environment. Please refer to the install guide for more details.

conda create -n py37 python=3.7  # "py37" is conda environment name, you can use any name you like.
conda activate py37

pip install bigdl-orca 
pip install torch torchvision
pip install tqdm

Step 1: Init Orca Context

from bigdl.orca import init_orca_context, stop_orca_context

if cluster_mode == "local":  # For local machine
    init_orca_context(cores=4, memory="4g")
elif cluster_mode == "k8s":  # For K8s cluster
    init_orca_context(cluster_mode="k8s", num_nodes=2, cores=2, memory="4g", master=..., container_image=...)
elif cluster_mode == "yarn":  # For Hadoop/YARN cluster
    init_orca_context(cluster_mode="yarn", num_nodes=2, cores=2, memory="4g")

This is the only place where you need to specify local or distributed mode. View Orca Context for more details.

Please check the tutorials if you want to run on Kubernetes or Hadoop/YARN clusters.

Step 2: Define the Model

You may define your model, loss and optimizer in the same way as in any standard (single node) PyTorch program.

import torch
import torch.nn as nn
import torch.nn.functional as F

class LeNet(nn.Module):
    def __init__(self):
        super(LeNet, self).__init__()
        self.conv1 = nn.Conv2d(1, 20, 5, 1)
        self.conv2 = nn.Conv2d(20, 50, 5, 1)
        self.fc1 = nn.Linear(4*4*50, 500)
        self.fc2 = nn.Linear(500, 10)

    def forward(self, x):
        x = F.relu(self.conv1(x))
        x = F.max_pool2d(x, 2, 2)
        x = F.relu(self.conv2(x))
        x = F.max_pool2d(x, 2, 2)
        x = x.view(-1, 4*4*50)
        x = F.relu(self.fc1(x))
        x = self.fc2(x)
        return F.log_softmax(x, dim=1)

loss = nn.NLLLoss()

You need to define a Model Creator Function that takes the parameter config and returns an instance of your PyTorch model, and an Optimizer Creator Function that takes two parameters model and config and returns an instance of your PyTorch optimizer.

def model_creator(config):
    model = LeNet()
    return model

def optim_creator(model, config):
    return torch.optim.Adam(model.parameters(), lr=config.get("lr", 0.001))

Step 3: Define Train Dataset

You can define the dataset using a Data Creator Function that has two parameters config and batch_size and returns a Pytorch DataLoader. Orca also supports Spark DataFrame and Orca XShards.

from torchvision import datasets, transforms

dir = '/tmp/dataset'

def train_loader_creator(config, batch_size):
    train_loader = torch.utils.data.DataLoader(
        datasets.MNIST(dir, train=True, download=True,
                       transform=transforms.Compose([
                           transforms.ToTensor(),
                           transforms.Normalize((0.1307,), (0.3081,))
                       ])),
        batch_size=batch_size, shuffle=True)
    return train_loader

def test_loader_creator(config, batch_size):
    test_loader = torch.utils.data.DataLoader(
        datasets.MNIST(dir, train=False,
                       transform=transforms.Compose([
                           transforms.ToTensor(),
                           transforms.Normalize((0.1307,), (0.3081,))
                       ])),
        batch_size=batch_size, shuffle=False)
    return test_loader

Step 4: Fit with Orca Estimator

First, Create an Orca Estimator for PyTorch.

from bigdl.orca.learn.pytorch import Estimator 
from bigdl.orca.learn.metrics import Accuracy

est = Estimator.from_torch(model=model_creator, optimizer=optim_creator, loss=loss,
                           metrics=[Accuracy()], use_tqdm=True)

Next, fit and evaluate using the Estimator.

batch_size = 64

train_stats = est.fit(data=train_loader_creator, epochs=1, batch_size=batch_size)
eval_stats = est.evaluate(data=test_loader_creator, batch_size=batch_size)
print(eval_stats)

Step 5: Save and Load the Model

Save the Estimator states (including model and optimizer) to the provided model path.

est.save("mnist_model")

Load the Estimator states (including model and optimizer) from the provided model path.

est.load("mnist_model")

Note: You should call stop_orca_context() when your application finishes.

That’s it, the same code can run seamlessly on your local laptop and scale to Kubernetes or Hadoop/YARN clusters.