error when using run_deplyment function in self-hosted prefect server

[akfmdl]

Bug summary

I set up a self-hosted Prefect server using the Prefect server Helm chart The image needs to be manually specified, so I applied the latest version compatible with that—2.19.9-python3.12-kubernetes. However, when deploying the code via run_deployment, an error occurs if the Python version in the local virtual environment differs, even slightly (e.g., a minor version mismatch). But, when I include the as_subflow=False option in run_deployment(), the error does not occur.

Error location

The error occurs in the create_task_run function of the PrefectClient class, specifically in the following code:

response = await self._client.post(
    "/task_runs/", json=task_run_data.dict(json_compatible=True)
)

Error message

prefect.exceptions.PrefectHTTPStatusError: Client error '409 Conflict' for url 'https://.../api/task_runs/'
Response: {'detail': 'Data integrity conflict. This usually means a unique or foreign key constraint was violated. See server logs for details.'}
For more information check: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/409
13:33:06.296 | ERROR   | Flow run 'just-chameleon' - Finished in state Failed("Flow run encountered an exception. PrefectHTTPStatusError: Client error '409 Conflict' for url 'https://.../api/task_runs/'\nResponse: {'detail': 'Data integrity conflict. This usually means a unique or foreign key constraint was violated. See server logs for details.'}\nFor more information check: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/409")

Version info (prefect version output)

image version: 2.19.9-python3.12-kubernetes
helm chart version: 2024.10.15184517
prefect version 2.19.9

Additional context

No response

[jahnavi0102]

Reason: When you run a flow or deployment in Prefect, metadata and state information about tasks, flows, and environments (such as Python version, package versions, etc.) are passed between the local environment and the Prefect server.

• Minor Version Differences: If the Python version in your local virtual environment is slightly different from the Python version on the server (for example, 3.12.0 locally and 3.12.1 on the server), this might result in differences in how certain dependencies or runtime behavior are handled.
• Metadata Conflict: Prefect tries to create task runs that inherit metadata from the local environment, including the environment's Python version. If the Prefect server sees a discrepancy in expected metadata, it may raise a data integrity conflict, especially if it attempts to reuse or update task metadata based on outdated or incompatible Python versions.
• The 409 Conflict error happens when Prefect's server-side database detects a data integrity violation — usually related to unique or foreign key constraints (e.g., the same task run ID or state is already stored and now conflicts with a new entry due to a version mismatch).

Why as_subflow=False Avoids the Error: When you include theas_subflow=False option in run_deployment(), you prevent the flow from running as a subflow of the parent flow.

This means: Independent Flow Execution: Prefect treats the deployment as an entirely separate, standalone flow, not linked to any parent flow. This changes how task metadata (including versioning and task run IDs) is handled. Prefect doesn't attempt to reuse or pass metadata between the parent flow and the subflow. No Metadata Inheritance: The task runs don't inherit metadata (like Python versions or task run IDs) from the parent flow, which avoids triggering a conflict in the Prefect server. In essence, the as_subflow=False option isolates the subflow and ensures that it is not dependent on the state or metadata of the parent flow. This effectively avoids the error, but it also means that the flow is now independent and will not share context, state, or any other data with the parent flow.