What causes "fallback_backend_failed" in ZhuLinsen/daily_stock_analysis?

Inspect details['fallback_error'] / the chained exception to identify what the fallback backend actually threw and fix that root cause first.

ZhuLinsen/daily_stock_analysis · critical · GenerationError

unknown_backend_error

unknown_backend_error

Error message

fallback_backend_failed

What it means

GenerationError with code UNKNOWN_BACKEND_ERROR raised at stage 'fallback' when the primary backend already raised a GenerationError (exc) and the subsequent fallback backend attempt failed with an unexpected non-GenerationError exception (fallback_exc). The 'reason' detail is 'fallback_backend_failed'; the error preserves both the primary error and the raw fallback exception in details for diagnosis. retryable and fallbackable are both False because the chain is exhausted.

Source

Thrown at src/analyzer.py:3062

                        "reason": "fallback_backend_failed",
                        "primary_error": {
                            "error_code": exc.error_code.value,
                            "backend": exc.backend,
                            "provider": exc.provider,
                            "stage": exc.stage,
                            "details": exc.details,
                        },
                        "fallback_error": {
                            "error_code": fallback_exc.error_code.value,
                            "backend": fallback_exc.backend,
                            "provider": fallback_exc.provider,
                            "stage": fallback_exc.stage,
                            "details": fallback_exc.details,
                        },
                    },
                ) from fallback_exc
            except Exception as fallback_exc:
                raise GenerationError(
                    error_code=GenerationErrorCode.UNKNOWN_BACKEND_ERROR,
                    stage="fallback",
                    retryable=False,
                    fallbackable=False,
                    backend=fallback_backend_id,
                    provider=fallback_backend_id,
                    details={
                        "reason": "fallback_backend_failed",
                        "primary_error": {
                            "error_code": exc.error_code.value,
                            "backend": exc.backend,
                            "provider": exc.provider,
                            "stage": exc.stage,
                            "details": exc.details,
                        },
                        "fallback_error": str(fallback_exc),
                    },
                ) from fallback_exc

View on GitHub (pinned to 5159bd72e8)

Solutions

Inspect details['fallback_error'] / the chained exception to identify what the fallback backend actually threw and fix that root cause first.
Verify the fallback backend's credentials, model list, and dependencies are complete — partial fallback config is the most common cause.
If the primary error (details['primary_error']) is itself retryable, fix or retry the primary path rather than relying on the broken fallback.
As a last resort, add another healthy fallback backend or disable the broken one so the chain degrades cleanly.

Defensive patterns

Strategy: fallback

Try / catch

from src.analyzer import GenerationError

try:
    result = run_generation(...)
except GenerationError as e:
    if e.details.get("reason") == "fallback_backend_failed":
        log_primary = e.details["primary_error"]
        log_fallback = e.details.get("fallback_exc")
        # both backends broken: do not retry blindly; alert ops / degrade to cached report
    raise

Prevention

Health-check every configured backend at startup, not just the primary.
Keep fallback backend credentials and deps fully configured — partial fallback config is the top cause.
Preserve and log details['primary_error'] to avoid fixing the wrong backend.

When it happens

Trigger: Generation with a primary + fallback backend configured (e.g. litellm primary, another provider fallback) where the primary fails with a structured GenerationError AND the fallback attempt throws an arbitrary exception (network TypeError, missing dependency, bad config) that is not itself a GenerationError.

Common situations: Fallback provider env vars not configured (key missing -> AttributeError/KeyError in its client); a version change in the fallback SDK raising a new exception type; transient network outage hitting both backends where the fallback fails before producing a structured error.

Related errors

AI-assisted analysis of ZhuLinsen/daily_stock_analysis@5159bd72e8 (2026-08-15). Data as JSON: /api/errors/076c3038b1a82868. Report an issue: GitHub.