mlflow/mlflow · warning · UserWarning

Failure attempting to register request header provider "{}":

Error message

Failure attempting to register request header provider "{}": {}

What it means

The request-header provider registry loads `mlflow.request_header_provider` entry points. Plugins that raise AttributeError or ImportError at import time produce this warning and are skipped, so their headers will not be attached to outgoing requests.

Source

Thrown at mlflow/tracking/request_header/registry.py:28

from mlflow.utils.plugins import get_entry_points

_logger = logging.getLogger(__name__)


class RequestHeaderProviderRegistry:
    def __init__(self):
        self._registry = []

    def register(self, request_header_provider):
        self._registry.append(request_header_provider())

    def register_entrypoints(self):
        """Register tracking stores provided by other packages"""
        for entrypoint in get_entry_points("mlflow.request_header_provider"):
            try:
                self.register(entrypoint.load())
            except (AttributeError, ImportError) as exc:
                warnings.warn(
                    'Failure attempting to register request header provider "{}": {}'.format(
                        entrypoint.name, str(exc)
                    ),
                    stacklevel=2,
                )

    def __iter__(self):
        return iter(self._registry)


_request_header_provider_registry = RequestHeaderProviderRegistry()
_request_header_provider_registry.register(DatabricksRequestHeaderProvider)
_request_header_provider_registry.register(DefaultRequestHeaderProvider)

_request_header_provider_registry.register_entrypoints()


def resolve_request_headers(request_headers=None):

View on GitHub (pinned to 6a27f2decc)

Solutions

Fix or reinstall the plugin named in the warning.
Uninstall the plugin if its headers are not needed.
Recreate the environment to clear stale/broken entry points.

Example fix

// before
import my_header_provider  # AttributeError: module has no attribute 'MyProvider'
// after
# pip install --force-reinstall my-mlflow-header-provider

Defensive patterns

Strategy: validation

Validate before calling

from importlib.metadata import entry_points
for ep in entry_points(group="mlflow.request_header_provider"):
    try:
        ep.load()
    except Exception as e:
        print(f"broken header provider {ep.name}: {e}")

Try / catch

import warnings
with warnings.catch_warnings(record=True) as w:
    warnings.simplefilter("always")
    client.search_experiments()
for warn in w:
    if "request header provider" in str(warn.message):
        fix_plugin(warn)

Prevention

Verify header providers load after every environment rebuild.
Declare all plugin dependencies explicitly in package metadata.
Watch for this warning when custom headers (e.g. tracing IDs) silently stop being sent.

When it happens

Trigger: Any installed package exposing mlflow.request_header_provider whose module/class fails on load.

Common situations: Header-injection plugins (e.g. tracing/correlation-id providers) broken after environment changes or partial upgrades.

Related errors

AI-assisted analysis of mlflow/mlflow@6a27f2decc (2026-08-29). Data as JSON: /api/errors/6b8754c3463e029b. Report an issue: GitHub.