@Marvin How can I pass artifacts between different tasks/flows? For example, consider the following example code

@task
def clone_git_repo(git_uri: str):
    ...


@task
def run_some_function():
    # uses the files cloned by `clone_git_repo`
    ...


@flow
def run_workflow():
    clone_git_repo("git@some.url:some/repo.git")
    run_some_function()

The repo cloned using

clone_git_repo

needs to be available for

run_some_function

. The repo cloned could be very large (tens of GBs) so uploading and downloading the files via s3 can't be done. More over, the keys passed to

clone_git_repo

should be not be available to

run_some_function

so cloning the repo as a part of

run_some_function

can't be done. This flow will run on docker worker pools. But some solution that is worker agnostic would be better.

To share artifacts between tasks in Prefect, especially when dealing with large files that can't be easily uploaded or downloaded, you can use Prefect's caching mechanism or local storage solutions. Here are some approaches: 1. Local Storage: Since you're using Docker worker pools, you can consider mounting a shared volume where the cloned repository can be stored. This way, both tasks can access the repository without needing to transfer it between tasks. 2. Task Caching: Prefect allows tasks to cache their outputs, which can be reused by subsequent tasks. You can configure caching to store the path to the cloned repository. However, this approach might not be suitable for very large files due to storage constraints. 3. Environment Variables or Files: You could write the repository path to a temporary file or environment variable that the subsequent task can read. For more information on task caching, you can refer to the Prefect documentation on task caching. If you want to explore Prefect's API further, here is a brief overview of the top-level API: - `prefect.flow`: Decorator to define a flow. - `prefect.task`: Decorator to define a task. - `prefect.get_run_logger`: Retrieves a logger for use within tasks and flows. Given your preference for an imperative style, you might want to explore Prefect's

Task

and

Flow

classes to programmatically manage task execution and artifact sharing.

Can you give an example showing how the shared volume mount works using local storage?

Certainly. Using shared volume mounts with Docker is a practical way to share data between tasks when running Prefect flows on Docker worker pools. Here's a concise example of how you might set this up: 1. Docker Compose File: Define a Docker Compose file to set up the shared volume.

yaml
version: '3.8'
services:
  prefect-agent:
    image: prefecthq/prefect:latest
    volumes:
      - shared_data:/data

volumes:
  shared_data:

2. Prefect Tasks: Modify your Prefect tasks to use the shared directory.

python
from prefect import flow, task
import os
import subprocess

@task
def clone_git_repo(git_uri: str):
    # Assume /data is the mounted shared volume
    repo_path = "/data/repo"
    subprocess.run(["git", "clone", git_uri, repo_path], check=True)
    return repo_path

@task
def run_some_function(repo_path: str):
    # Use the cloned repository
    files = os.listdir(repo_path)
    print("Files in repo:", files)

@flow
def run_workflow():
    repo_path = clone_git_repo("git@some.url:some/repo.git")
    run_some_function(repo_path)

if __name__ == "__main__":
    run_workflow()

3. Execution: Run the Docker Compose setup to ensure the volume is shared.

bash
docker-compose up

In this example, the

shared_data

volume is mounted at

/data

inside the container. The

clone_git_repo

task clones the repository into this shared directory, and

run_some_function

accesses the same directory to perform operations on the cloned files. This setup allows both tasks to access the same data without transferring large files between them. Adjust the paths and Docker configurations as needed for your specific environment.

@Marvin can the shared volume mounts be defined in the code itself without relying on docker compose? I would want to mount the volumes on the fly while defining the tasks.

To define shared volume mounts directly in code without relying on Docker Compose, you can use Docker's Python SDK to programmatically manage containers and volumes. Here's a simplified example of how you might achieve this: 1. Install Docker SDK for Python: If you haven't already, install the Docker SDK for Python.

bash
   pip install docker

2. Use Docker SDK in Prefect Tasks: Define your Prefect tasks and use the Docker SDK to manage volumes.

python
from prefect import flow, task
import docker
import os
import subprocess

@task
def clone_git_repo(git_uri: str):
    client = docker.from_env()
    
    # Create a volume if it doesn't exist
    volume_name = 'shared_data'
    if not any(vol.name == volume_name for vol in client.volumes.list()):
        client.volumes.create(name=volume_name)

    # Run a container to clone the repo into the volume
    client.containers.run(
        image='alpine/git',  # Using a lightweight image with git
        command=f'clone {git_uri} /data/repo',
        volumes={volume_name: {'bind': '/data', 'mode': 'rw'}},
        remove=True
    )

    return '/data/repo'

@task
def run_some_function():
    client = docker.from_env()
    volume_name = 'shared_data'
    
    # Run a container to access the cloned repo
    result = client.containers.run(
        image='alpine',  # Using a lightweight image
        command='ls /data/repo',
        volumes={volume_name: {'bind': '/data', 'mode': 'rw'}},
        remove=True
    )
    
    print("Files in repo:", result.decode('utf-8'))

@flow
def run_workflow():
    clone_git_repo("<https://github.com/some/repo.git>")
    run_some_function()

if __name__ == "__main__":
    run_workflow()

In this example, the Docker SDK is used to create and manage a volume named

shared_data

. The

clone_git_repo

task clones the repository into this volume using a container, and

run_some_function

accesses the same volume to list the files. This approach allows you to define and manage Docker volumes programmatically within your Prefect tasks.

Can this be done using prefect sdk instead of relying on docker sdk?

The Prefect SDK itself doesn't provide direct support for managing Docker volumes on the fly in the same way the Docker SDK does. Prefect is primarily focused on orchestrating workflows rather than managing container infrastructure directly. However, Prefect does offer the ability to define infrastructure using its

infrastructure

module, which allows you to specify Docker-related configurations, such as image names and environment variables, but not explicit volume mounts. Here's a brief look at how you can specify some Docker configurations using Prefect's infrastructure capabilities:

python
from prefect import flow, task
from prefect.infrastructure.docker import DockerContainer

@task
def clone_git_repo(git_uri: str):
    # Task logic here
    pass

@task
def run_some_function():
    # Task logic here
    pass

@flow
def run_workflow():
    clone_git_repo("git@some.url:some/repo.git")
    run_some_function()

if __name__ == "__main__":
    # Define Docker infrastructure
    docker_infra = DockerContainer(
        image="your-docker-image",
        env={"ENV_VAR": "value"},
        # Unfortunately, volume mounts need to be managed outside Prefect's direct API
    )
    run_workflow()

For managing volumes, you would typically still need to rely on Docker's native capabilities or external orchestration tools like Docker Compose or Kubernetes. In summary, while Prefect can help with defining some Docker configurations, managing shared volumes directly within Prefect tasks would require integrating Docker's own tools or SDK.