Troubleshooting¶

This guide covers the most common production and local issues when integrating azure-functions-logging.

Logs Not Showing in Azure¶

Symptoms¶

Handler code runs, but expected logs are missing.
Only warnings/errors appear, while info/debug do not.

Root Cause¶

host.json log level policy is more restrictive than application intent.

Checks¶

Inspect host configuration:

{
  "logging": {
    "logLevel": {
      "default": "Warning"
    }
  }
}

If app setup is INFO, Warning host policy suppresses info events.

Resolution¶

Adjust host defaults or function-specific overrides:

{
  "logging": {
    "logLevel": {
      "default": "Information",
      "Function.MyFunction": "Information"
    }
  }
}

Warning

In Azure-hosted execution, host policy is authoritative for emitted levels.

Duplicate Log Lines¶

Symptoms¶

Every log appears twice or more.

Root Cause¶

Multiple handlers are attached along logger hierarchy.

Typical causes:

Existing logging setup plus package setup both attach handlers.
Multiple frameworks configure root independently.
logging.basicConfig() used alongside custom setup.

Resolution¶

Pick one owner for handler configuration.
Call setup_logging() once in startup path.
Remove duplicate root handlers in your app configuration.

host.json Conflict Warning Appears¶

Meaning¶

The library detected host policy that can suppress lower log levels than your configured level.

Action¶

Review host.json log level defaults.
Align defaults with operational visibility needs.
Keep stricter per-category levels only where justified.

This warning is informational but usually points to real missing telemetry.

Cold Start Not Detected¶

Symptoms¶

cold_start always False.
cold_start always None.

Root Causes¶

inject_context(context) not called.
Context injection occurs after first log event.
Warm worker process already handled previous invocation.

Resolution¶

Call inject_context(context) first in every handler:

def main(req, context):
    inject_context(context)
    logger.info("invocation started")

To observe cold start locally:

Restart local host.
Send first request.
Check first event for cold_start=true.

JSON Format Issues¶

Symptoms¶

Downstream parser fails to parse events.
Missing custom fields in JSON output.

Root Causes¶

Log sink expects multiline JSON instead of NDJSON.
Custom fields passed incorrectly.
Non-JSON preprocessing modifies log lines.

Resolution¶

Ensure one JSON object per line is accepted.
Pass extra fields via keyword args in logger calls.
Avoid shell transformations that corrupt line boundaries.

Correct pattern:

logger.info("order accepted", order_id="o-123", tenant_id="t-1")

Color Output Looks Wrong¶

Symptoms¶

ANSI escape sequences appear literally.
Colors not rendered in terminal.

Root Cause¶

Terminal or sink does not render ANSI color codes.

Resolution¶

Use JSON mode in non-interactive or pipeline environments:

setup_logging(format="json")

Keep color mode for local interactive terminal sessions.

setup_logging Has No Effect¶

Symptoms¶

Later setup_logging(...) calls do not change behavior.

Root Cause¶

Idempotency: first setup call wins.

Resolution¶

Ensure desired setup call executes first.
Consolidate startup configuration in one module.

Invocation Fields Are Missing¶

Symptoms¶

invocation_id, function_name, or trace_id is None.

Root Causes¶

inject_context(context) omitted.
Context object lacks expected attributes.
Logging occurs before context injection.

Resolution¶

Inject context at entrypoint before any logs.
Verify function signature includes context.

Third-Party Logs Too Noisy¶

Symptoms¶

Dependency logs dominate output and hide app events.

Resolution¶

Reduce dependency logger levels:

import logging

logging.getLogger("urllib3").setLevel(logging.WARNING)
logging.getLogger("azure").setLevel(logging.WARNING)

Use INFO for application events and WARNING for noisy dependencies.

Bound Context Leaks Across Requests¶

Symptoms¶

Request identifiers from one invocation appear in another.

Root Cause¶

A bound logger with request keys was reused globally.

Resolution¶

Create bound loggers per invocation.
Do not cache request-scoped bound loggers at module level.

Safe pattern:

request_logger = logger.bind(request_id=current_request_id)
request_logger.info("request started")

Azure vs Local Behavior Confusion¶

Clarification¶

Local standalone setup may add handlers and formatter directly. Azure/Core Tools setup installs filter-only behavior to avoid duplicate host output.

This difference is intentional and expected.

Fast Diagnostic Checklist¶

Run through this list during incidents:

Confirm setup_logging() called exactly once.
Confirm inject_context(context) called first in handler.
Confirm output format matches sink expectations.
Confirm host.json level policy allows required severity.
Confirm no duplicate root handlers.
Confirm bound loggers are request-scoped.

Need More Help¶

Use these references for deeper checks:

If behavior still looks wrong, create a minimal reproducible snippet showing setup code, one handler, and one observed log line.