@Marvin if i want to trigger a flow off of another flow - for example from an event/webhook - how can i pass in parameters from the upstream flow?

To trigger a flow from another flow in Prefect 3.x, and pass parameters between them, you can use Prefect's event-driven capabilities and deployments. Here's a concise guide: 1. Triggering Flows: You can set up a deployment for the downstream flow and use an event or webhook to trigger it. Prefect allows you to specify triggers using

DeploymentTrigger

. You can match events from an upstream flow to trigger the downstream flow. 2. Passing Parameters: When you trigger a flow via the Prefect API, you must pass parameters as keyword arguments. Ensure that these parameters are validated and do not exceed 512kb in size. 3. Example Setup: - Define your upstream and downstream flows using the

@flow

decorator. - Use

tags

to identify the upstream flow runs you want to trigger the downstream flow from. - Configure

DeploymentTrigger

in your downstream flow to listen for specific events from the upstream flow. Here's a simplified example based on the gathered information:

python
from prefect import flow, tags
from prefect.events.schemas import DeploymentTrigger

TAG_NAME = "example_tag"

@flow
def upstream_flow(param1):
    # Your upstream logic
    pass

@flow
def downstream_flow(param2):
    # Your downstream logic
    pass

if __name__ == "__main__":
    with tags(TAG_NAME):
        upstream_flow(param1="value1")

    downstream_flow.serve(
        name="downstream",
        triggers=[
            DeploymentTrigger(
                expect={"prefect.flow-run.Completed"},
                match_related=[
                    {
                        "prefect.resource.role": "tag",
                        "prefect.resource.id": f"prefect.tag.{TAG_NAME}",
                    },
                    {
                        "prefect.resource.role": "flow",
                        "prefect.resource.name": "upstream_flow",
                    }
                ]
            )
        ]
    )

For more details, you can refer to the Prefect documentation on writing flows and automations and triggers. If you need further assistance or examples, feel free to ask.