Hello World

This is a self contained guide on how to build a simple app and component spec and launch it via two different schedulers.

See the Quickstart for how to install TorchX locally before following this example.

Lets start off with writing a simple “Hello World” python app. This is just a normal python program and can contain anything you’d like.

NOTE: This example uses Jupyter Notebook %%writefile to create local files for example purposes. Under normal usage you would have these as standalone files.

%%writefile my_app.py

import sys
import argparse

def main(user: str) -> None:
    print(f"Hello, {user}!")

if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        description="Hello world app"
    )
    parser.add_argument(
        "--user",
        type=str,
        help="the person to greet",
        required=True,
    )
    args = parser.parse_args(sys.argv[1:])

    main(args.user)

Overwriting my_app.py

Now that we have an app we can write the component file for it. This function allows us to reuse and share our app in a user friendly way.

We can use this component from the torchx cli or programmatically as part of a pipeline.

%%writefile my_component.py

import torchx.specs as specs

def greet(user: str, image: str = "my_app:latest") -> specs.AppDef:
    """
    Echos a message to stdout (calls /bin/echo)

    Args:
        user: name of the person to greet
        image: image to use
    """
    return specs.AppDef(
        name="hello_world",
        roles=[
            specs.Role(
                name="greeter",
                image=image,
                entrypoint="python",
                args=[
                    "-m", "my_app",
                    "--user", user,
                ],
            )
        ],
    )

Overwriting my_component.py

Once we write our component, we can then call it via torchx run. The local_cwd scheduler executes the component relative to the current directory.

%%sh
torchx run --scheduler local_cwd my_component.py:greet --user "your name"

Hello, your name!
local_cwd://torchx/hello_world_ed42ed11

torchx 2021-10-18 11:48:45 INFO     Waiting for the app to finish...
torchx 2021-10-18 11:48:46 INFO     Job finished: SUCCEEDED

If we want to run in other environments, we can build a Docker container so we can run our component in Docker enabled environments such as Kubernetes or via the local Docker scheduler.

NOTE: this requires Docker installed and won’t work in environments such as Google Colab.

%%writefile Dockerfile

FROM ghcr.io/pytorch/torchx:0.1.0rc1

ADD my_app.py .

Overwriting Dockerfile

Once we have the Dockerfile created we can create our docker image.

%%sh
docker build -t my_app:latest -f Dockerfile .

Step 1/2 : FROM ghcr.io/pytorch/torchx:0.1.0rc1
 ---> 15fd31611433
Step 2/2 : ADD my_app.py .
 ---> Using cache
 ---> 9cedd7f457fb
Successfully built 9cedd7f457fb
Successfully tagged my_app:latest

We can then launch it on the local scheduler.

%%sh
torchx run --scheduler local_docker my_component.py:greet --image "my_app:latest" --user "your name"

Hello, your name!
local_docker://torchx/hello_world_0619d6b3

Error response from daemon: pull access denied for my_app, repository does not exist or may require 'docker login': denied: requested access to the resource is denied
torchx 2021-10-18 11:48:48 WARNING  failed to fetch image my_app:latest, falling back to local: Command '['docker', 'pull', 'my_app:latest']' returned non-zero exit status 1.
torchx 2021-10-18 11:48:48 INFO     Waiting for the app to finish...
WARNING: IPv4 forwarding is disabled. Networking will not work.
torchx 2021-10-18 11:48:49 INFO     Job finished: SUCCEEDED

If you have a Kubernetes cluster you can use the Kubernetes scheduler to launch this on the cluster instead.