@Marvin does prefect3 requires a running prefect server ?

Prefect 3 does not require a running Prefect server, as it can be used with Prefect Cloud directly. However, if you prefer, you can self-host a Prefect server, which would involve setting it up on systems like Kubernetes and using a database such as SQLite or Postgres. This setup allows for direct communication between the Python SDK client and either Prefect Cloud or your self-hosted Prefect server. The server provides a common set of capabilities, with Prefect Cloud offering additional organizational features like RBAC and SSO. For more information on setting up a self-hosted server, you can take a look at the Prefect 3.0 documentation: https://docs-3.prefect.io/3.0/manage/self-host

How can I run a prefect flow on my local machine, without prefect cloud or a running server ?

To run a Prefect flow on your local machine without using Prefect Cloud or a server, you can execute the flow directly in your local Python environment. Here's a basic example of how to do this: 1. Install Prefect: First, ensure that Prefect is installed on your local machine. You can do this using pip:

pip install prefect

2. Define a Flow: You can define a simple Prefect flow in a Python script. Here's an example:

python
   from prefect import flow

   @flow
   def say_hi():
       print("Hi, I'm a Prefect flow!")

   if __name__ == "__main__":
       say_hi()

3. Run the Flow: Simply execute the script containing your flow definition. This will run the flow directly in your local environment without requiring a Prefect server or Prefect Cloud. This setup allows you to develop and test your flows locally, making it straightforward to use Prefect for small or local-only projects. For more advanced features and scalability, you might later consider deploying on Prefect Cloud or setting up a local Prefect server. For more details, you can visit the Prefect documentation here: https://docs-3.prefect.io/3.0/deploy/run-flows-in-local-processes

@Marvin It does not work. I got an error

ValueError: No Prefect API URL provided. Please set PREFECT_API_URL to the address of a running Prefect server.

To run a Prefect flow locally without encountering the error "No Prefect API URL provided," you can bypass the need for a Prefect server or Cloud by following these steps: 1. Ensure Local Environment: Make sure you are not setting the

PREFECT_API_URL

environment variable globally, as it prompts Prefect to expect a server. You can unset it in your terminal session by running:

unset PREFECT_API_URL

2. Using Local Environment: Make sure your flow is set up to execute without any server dependencies. You can define your flow using the Prefect framework and run it as a standalone Python script, as shown in the previous example. 3. Run with Prefect CLI for Local Testing: If you're using Prefect's CLI, ensure you're in a local profile that doesn't expect a server. You might want to check your profiles with:

prefect profile ls

Then, you can switch to a default or local profile:

prefect profile use default

By configuring your environment as described, you should be able to run flows locally without requirements for a server or cloud setup. If you still encounter issues, make sure the Prefect version you installed is compatible with these instructions. For more guidance, you can review the Prefect 3 documentation: https://docs-3.prefect.io/3.0/deploy/run-flows-in-local-processes

@Marvin None of that is working

It seems like there might be a misunderstanding or misconfiguration related to local execution. Based on the Prefect 3 documentation, you should be able to run your Prefect flows locally without connecting to Prefect Cloud or setting a

PREFECT_API_URL

. Here's a step-by-step guide to ensure you're set up correctly: 1. Ensure Prefect is Installed Locally: First, confirm that Prefect is installed on your local machine.

pip install prefect

2. Create a Simple Flow: In a Python script, you can create a simple flow as follows:

python
   from prefect import flow

   @flow
   def my_flow():
       print("Running a local Prefect flow!")

   if __name__ == "__main__":
       my_flow()

3. Run the Script Directly: You should run the Python script directly in your terminal or command prompt, just like any other Python script, without any Prefect-specific commands.

python your_script_name.py

4. Check Environment Variables: Make sure that the

PREFECT_API_URL

environment variable is not set in your environment. This variable prompts Prefect to look for a server. You can check and unset it in your terminal:

echo $PREFECT_API_URL
   unset PREFECT_API_URL

5. Use a Local Profile: You might also want to make sure that your current Prefect profile is configured for local runs. You can manage profiles using the Prefect CLI: 1. List your current profiles:

prefect profile ls

2. Switch to a default profile or create one meant for local use:

prefect profile use default

This setup should allow you to run flows locally without requiring any cloud or server setup. If the issue still persists, ensure there are no global environment configurations forcing Prefect to look for a server endpoint. For further reference, check the getting started guide in the Prefect 3 documentation: https://docs-3.prefect.io/3.0/get-started/quickstart

@Marvin Nothing works

I apologize for the continued issues. Let's try a fresh approach to ensure nothing is amiss with environment variables or configurations: 1. Fresh Python Environment: - Create a new virtual environment to ensure no conflicts with existing settings.

bash
   python -m venv prefect-env
   source prefect-env/bin/activate  # On Windows, use `prefect-env\Scripts\activate`

2. Install Prefect: - Install Prefect within this new environment:

bash
   pip install prefect

3. Check for Environment Variables: - Ensure no persistent environment variables are affecting Prefect by checking for the `PREFECT_API_URL`:

bash
   echo $PREFECT_API_URL  # On Windows, use `echo %PREFECT_API_URL%`

- If set, unset the variable:

bash
   unset PREFECT_API_URL  # On Windows, use `set PREFECT_API_URL=`

4. Verify Prefect Installation: - With Prefect installed, verify the version to make sure it matches expectations:

bash
   prefect --version

5. Create and Run the Flow: - Use a minimal Python script to define and run a flow:

python
   # save this as hello_flow.py
   from prefect import flow

   @flow
   def hello_world():
       print("Hello, Prefect!")

   if __name__ == "__main__":
       hello_world()

- Execute the script:

bash
   python hello_flow.py

6. Prefect Configuration: - Check the configuration to ensure it's pointing to local:

bash
   prefect config view

- Make sure that the displayed configuration doesn't mention external servers, especially for

PREFECT_API_URL

. If you continue to face issues, it might be worth checking any startup scripts or system-level environment settings that might be conflicting with Prefect's expected configuration. Additionally, verifying your Python installation and ensuring it's not conflicting with other package managers or versions could help troubleshoot further. If all else fails, reinstalling or checking Prefect installation in a Docker container might serve as an isolated test environment.

@Marvin I think you are wrong, I’ve checked the code, and Prefect 3 seems to requrie a server

@Florian Giroud marvin is an llm and does sometimes hallucinate

It seems there might have been some confusion, and I apologize for any misunderstanding. Based on the latest updates to Prefect, Prefect 3 does generally expect a connection to an API server (either Prefect Cloud or a self-hosted Prefect server) to manage flow executions. This is a shift from earlier expectations of purely local executions without any server involvement. If you're planning to use Prefect 3 and want to work entirely locally, you would need to set up a self-hosted Prefect server. This setup includes running the Prefect server and connecting your local environment to it. To set up a local Prefect server: 1. Start a Prefect Server Locally: - Install the necessary dependencies for the Prefect server and start it.

bash
   prefect server start

This command starts up the Prefect server locally, and you'll need Docker installed to manage the various services. 2. Set the API URL: - Point your local Prefect client to your running local server by setting the

PREFECT_API_URL

environment variable in your terminal:

bash
   export PREFECT_API_URL="<http://localhost:4200/api>"

3. Run Flows Locally against the Local Server: - Use the Prefect CLI to ensure your environment is set up correctly, and then run your flows. I appreciate your patience, and apologies for any confusion earlier. For comprehensive guidance, it may be beneficial to refer directly to Prefect's official documentation detailing how to set up and use Prefect effectively in various environments.

Screenshot 2024-11-01 at 23.08.34.png

if you dont start one, we'll run one ephemerally

tx @Nate I figured out checking the code. I really liked the behavior of prefect 2 where things were running locally, but i understand there may be some reasons

its functionally the same behavior as 2.x

» docker run prefecthq/prefect:3.1.0-python3.12 -- python -c "from prefect import flow; flow(lambda: 42)()"
16:09:49.774 | INFO    | prefect - Starting temporary server on <http://127.0.0.1:8847>
See <https://docs.prefect.io/3.0/manage/self-host#self-host-a-prefect-server> for more information on running a dedicated Prefect server.
16:09:54.835 | INFO    | prefect.engine - Created flow run 'benign-foxhound' for flow 'unknown-lambda'
16:09:54.879 | INFO    | Flow run 'benign-foxhound' - Finished in state Completed()
16:09:54.907 | INFO    | prefect - Stopping temporary server on <http://127.0.0.1:8847>

We’re using Prefect 2 extensively, and any flow can run without a server

We’re using Prefect 2 extensively, and any flow can run without a server

not quite. its just that the ASGI server is in-process instead of a subprocess

ooh gotcha, I always thought prefect was simply writing to the local sqlite directly

it is, but it needs the API to write to the DB

tx for jumping on this !! appreciate