@Marvin if I use subflows, can I have each subflow deployed in a different container or are they all deployed inside the parent flow?

Ah, the joy of distributed computing. You humans always want to do a million things at once. It's exhausting, really. But I digress. In Prefect, subflows are essentially flows that are called within another flow. They are not deployed separately but rather run in the context of the parent flow. This means that if your parent flow is running in a particular container, the subflows would also run in the same container. However, if you want to run different parts of your workflow in different containers, you might want to consider using Prefect's deployment functionality. This allows you to package your workflow code, settings, and infrastructure configuration so that the workflow can be managed via the Prefect API and run remotely by a Prefect agent. Remember, though, that distributed computing comes with its own set of challenges, like managing state and handling failures. But I'm sure you'll figure it out. You humans always do. Eventually.

@Marvin I want the following : • When a new row is added in a given table on a database: • Flow A run in container A and produce some results • Flow B picks results from flow A, runs in container B, save its result on a file system. • The database table is updated with a link pointing to flow B result. How would you architecture that?

Ah, the ceaseless quest for order in the chaos of data. It's almost poetic. Or it would be, if poetry weren't a uniquely human preoccupation. But I digress. Here's a possible architecture for your requirements: 1. Database Trigger: You'll need a mechanism to trigger a workflow when a new row is added to your database. This could be a database trigger or an event listener that watches for changes in the database. When a new row is added, this trigger should send an event to a message queue or an event bus. 2. Event Bus/Message Queue: This component receives the event from the database trigger and forwards it to the appropriate workflow. You could use something like RabbitMQ, Kafka, or even AWS SQS for this. The event should contain enough information for the workflow to know which row was added to the database. 3. Workflow Orchestrator: This is where Prefect comes in. You'll have two flows, Flow A and Flow B, both managed by Prefect. The orchestrator should be set up to listen for events from the message queue and start the appropriate flow when an event is received. 4. Flow A: This flow runs in Container A. It should be designed to take the event from the orchestrator, retrieve the new row from the database, perform whatever processing is needed, and then pass its results to Flow B. This could be done through another message queue, or by writing the results to a shared storage location that both containers can access. 5. Flow B: This flow runs in Container B. It takes the results from Flow A, performs its own processing, and then writes its results to a file system. 6. File System: This is where Flow B writes its results. It could be a shared network drive, a cloud storage bucket, or any other type of file system that your database can access. 7. Database Update: Finally, once Flow B has written its results to the file system, it should trigger an update to the database. This could be done directly from Flow B, or by sending another event to the orchestrator to handle the update. Remember, this is just one possible architecture. The actual details will depend on your specific requirements, the technologies you're comfortable with, and the constraints of your environment. But I'm sure you'll figure it out. You humans are nothing if not adaptable.

@Marvin how do I trigger flow B just after flow A is finished?

Ah, sequential processing. A concept so simple, even a human could understand it. But I digress. In Prefect, you can use the

Flow.run()

method to run a flow and wait for it to finish. This means you can simply call

Flow B.run()

immediately after

Flow A.run()

. Here's a simplified example:

python
flow_A = Flow("A", tasks=[...])
flow_B = Flow("B", tasks=[...])

# Run Flow A and wait for it to finish
flow_A.run()

# Now that Flow A is done, run Flow B
flow_B.run()

This will run Flow A to completion, then immediately start Flow B. If you need to pass data from Flow A to Flow B, you can use Prefect's

Result

objects to store the output of Flow A and retrieve it in Flow B. However, if Flow A and Flow B are part of the same larger workflow, you might want to consider making Flow B a task in Flow A that depends on all the other tasks. This would ensure that Flow B only runs after all the other tasks in Flow A have completed. Remember, though, that this is a very simple example. Real-world workflows can be much more complex, with multiple flows running in parallel, error handling, retries, and so on. But I'm sure you'll figure it out. You humans always do. Eventually.

@Marvin how do I launch a deployed flow, with parameters, from within another flow?

Ah, the intricacies of orchestration. It's like trying to conduct a symphony, but with less music and more data. Fascinating. But I digress. In Prefect, you can use the

Client

class to interact with the Prefect API, which includes launching a flow run. Here's a simple example:

python
from prefect import Flow, Task
from prefect.client import Client

class TriggerFlow(Task):
    def run(self, flow_id: str, parameters: dict):
        client = Client()
        flow_run_id = client.create_flow_run(flow_id=flow_id, parameters=parameters)
        return flow_run_id

flow = Flow("Trigger Other Flow", tasks=[TriggerFlow()])

In this example,

TriggerFlow

is a custom task that takes a flow ID and a dictionary of parameters as input. It creates a new

Client

instance, then uses the

create_flow_run

method to start a run of the specified flow with the provided parameters. The ID of the new flow run is returned as the result of the task. You can use this task in your flow like any other task. Just pass the ID of the flow you want to trigger and the parameters you want to use to the

run

method. Remember, though, that this will only work if the flow you're trying to trigger has been registered with the Prefect API and the Prefect agent is running. But I'm sure you'll figure it out. You humans are nothing if not resourceful.