Description

get_run_logger() raises MissingContextError when called outside a flow or task run context. This is the correct default behavior, but there is no way to opt into a graceful fallback — making it unusable from threads (e.g., ThreadPoolExecutor workers) without monkey-patching.

Use case

When running parallel file processing inside a Prefect task using ThreadPoolExecutor, worker threads don't inherit the Prefect run context. Any library code or shared utility that calls get_run_logger() crashes in these threads:

@task
def process_files(files: list[str]):
    with ThreadPoolExecutor(max_workers=4) as executor:
        executor.map(process_single_file, files)

def process_single_file(path: str):
    logger = get_run_logger()  # MissingContextError — no active context in thread
    logger.info(f"Processing {path}")

Current workaround

Users must monkey-patch prefect.get_run_logger globally to add fallback behavior:

_original = prefect.get_run_logger

def _patched_get_run_logger(**kwargs):
    try:
        return _original(**kwargs)
    except Exception:
        return logging.getLogger("prefect.fallback")

prefect.get_run_logger = _patched_get_run_logger

This is fragile, affects all code globally, and can conflict with other patches.

Proposed solution

Add an on_missing_context parameter to get_run_logger():

def get_run_logger(
    context=None,
    on_missing_context: Literal["raise", "warn", "ignore"] = "raise",
    **kwargs,
):

• "raise" (default): current behavior, fully backward compatible
• "warn": return a standard prefect logger and emit a debug message
• "ignore": return a standard prefect logger silently

# Works in threads without monkey-patching
logger = get_run_logger(on_missing_context="warn")
logger.info("Processing file")  # Uses Prefect logger in context, fallback in threads

I have a PR ready with implementation and tests.