@Marvin I have a flow/deployment that i want to make sure can only run one at a time. The schedule is set to run every 5 minutes, but if it finds no new data to process it will exit. If it finds data to process it can take up to an hour. While that is running i dont want any new flow runs of that flow or deployment (doesnt really matter) to occur.

To ensure that your flow or deployment can only run one instance at a time, you can use concurrency limits. This feature allows you to define the maximum number of concurrent runs for a given flow. Here are some resources and steps to achieve this: 1. Concurrency Limits Documentation: Prefect provides a way to set concurrency limits using tags. You can find more details here: * https://docs.prefect.io/latest/concepts/automations/ 2. Concurrency Example: You can define a concurrency limit for your deployment as follows:

python
   from prefect import flow
   from prefect.deployments import Deployment

   @flow
   def my_flow():
       # Your flow logic here

   deployment = Deployment.build_from_flow(
       flow=my_flow,
       name="my_deployment",
       tags=["my_flow_tag"],              # Add a specific tag to your deployment
       work_queue_concurrency=1           # Set concurrency limit to 1
   )

   deployment.apply()

3. Use the Client for Advanced Control: You can programmatically set concurrency limits using the Prefect client, which might give you more control over dynamic scenarios. * Documentation: https://docs.prefect.io/latest/guides/using-the-client/ 4. Potential Issues and Fixes: * There are known issues with duplicate flow runs in specific environments like Kubernetes. For example, if a flow fails and retries, it can lead to duplicate executions. You can find a related GitHub issue here: * https://github.com/PrefectHQ/prefect/issues/12509 By setting an appropriate tag and concurrency limit, you can ensure that only one flow run is active at any given time, thus preventing overlapping executions.

@Marvin i have a deployment.yaml how would it look there?

To define a concurrency limit in your

deployment.yaml

, you will need to include a

work_queue_concurrency

parameter under your deployment configuration. Here is an example structure of how your

deployment.yaml

can look:

yaml
# Example deployment.yaml

name: my-deployment
work_pool_name: default-agent-pool
work_queue_name: my-work-queue
tags: ["my_flow_tag"]
schedule:
  cron: "*/5 * * * *"
  timezone: "UTC"
parameters: {}
infra_overrides: {}
infrastructure:
  type: process
  env: {}
  labels: {}
flow_name: my_flow_name
entrypoint: /path/to/your/flow.py:my_flow_function
path: /path/to/your/project/

# Concurrency Settings
work_queue_concurrency: 1  # This ensures only one run at a time

To apply the new deployment configuration with the concurrency limit:

sh
prefect deployment apply deployment.yaml

This approach sets a concurrency limit on the work queue associated with your deployment, ensuring that only one instance of the flow runs at any one time. Here are some supporting resources: * https://docs.prefect.io/latest/guides/global-concurrency-limits/ * https://docs.prefect.io/latest/concepts/deployments-block-based/ You can adjust the remaining parameters in

deployment.yaml

to match your specific configuration needs.