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Baldur

Baldur is a self-healing reliability layer for Python applications: circuit breaker, retry, fallback, and dead-letter queue behind one decorator.

import baldur


@baldur.protected("charge-customer")
def charge(order_id: str) -> dict:
    return payment_gateway.charge(order_id)

@baldur.protected(...) wraps your function in a composed resilience pipeline. With zero configuration it runs on an in-memory fallback — no Redis, no environment variables, no Docker. Add Redis when you go multi-process.

flowchart LR
    A["your call"] --> B{"@baldur.protected"}
    B --> C["dependency<br/>API · DB · queue"]
    B -. "transient failure" .-> D["retry + backoff"]
    B -. "dependency failing" .-> E["circuit breaker"]
    B -. "all retries fail" .-> F["fallback → dead-letter queue"]

Why Baldur exists

The failures that actually hurt happen inside your service, in the code path of a single call: a double-charged customer, one slow dependency dragging down every request, a payment lost to a transient error. Handling them well means writing the same circuit breaker, the same backoff, the same dead-letter plumbing in every project, by hand, correctly.

Baldur is that layer, written once and composed behind one decorator:

  • Framework-agnostic. One API across Django, FastAPI, and Flask.
  • No infrastructure required. It's a library, not a sidecar or a service.
  • Production-grade when you need it. Dead-letter queue, replay, and audit are there.

Get started

Pick your framework and you'll have a protected endpoint running:

License

Baldur is released under the Apache License 2.0.