Saga Orchestration

Patterns for managing distributed transactions and long-running business processes without two-phase commit.

Inputs and Outputs

What you provide:

Service boundaries and ownership (which service owns which step)
Transaction requirements (which steps must be atomic, which can be eventual)
Failure modes for each step (transient vs. permanent, retry policy)
SLA requirements per step (informs timeout configuration)
Existing event/messaging infrastructure (Kafka, RabbitMQ, SQS, etc.)

What this skill produces:

Saga definition with ordered steps, action commands, and compensation commands
Orchestrator or choreography implementation for your chosen pattern
Compensation logic for each participant service (idempotent, always-succeeds)
Step timeout configuration with per-step deadlines
Monitoring setup: state machine metrics, stuck saga detection, DLQ recovery

When to Use This Skill

Coordinating multi-service transactions without distributed locks
Implementing compensating transactions for partial failures
Managing long-running business workflows (minutes to hours)
Handling failures in distributed systems where atomicity is required
Building order fulfillment, approval, or booking processes
Replacing fragile two-phase commit with async compensation

Detailed section: Core Concepts

Moved to references/details.md.

Detailed section: Templates

Moved to references/details.md.

Best Practices

Do's

Make every step idempotent — Commands may be replayed on broker reconnect
Design compensations carefully — They are the most critical code path
Use correlation IDs — The saga_id must flow through every event and log
Implement per-step timeouts — Never wait indefinitely for a participant reply
Log state transitions — saga_id, step_name, old_state → new_state on every change
Test compensation paths explicitly — Inject failures at each step index in integration tests

Don'ts

Don't assume instant completion — Sagas are async and may take minutes
Don't skip compensation testing — The rollback path is the hardest to get right
Don't couple services directly — Use async messaging, never synchronous calls inside a saga step
Don't ignore partial failures — A step that partially executed still needs compensation
Don't use a global timeout — Each step has different latency characteristics

Troubleshooting

Saga stuck in COMPENSATING state

A saga enters compensation but never reaches FAILED. This means a compensation handler is throwing an unhandled exception and never publishing SagaCompensationCompleted. Add dead-letter queue (DLQ) handling to compensation consumers and ensure every compensation action publishes a result event even when the underlying operation was already rolled back.

async def handle_release_reservation(self, command: Dict):
    try:
        await self.release_reservation(command["original_result"]["reservation_id"])
    except ReservationNotFoundError:
        pass  # Already released — treat as success
    # Always publish completion, regardless of outcome
    await self.event_publisher.publish("SagaCompensationCompleted", {
        "saga_id": command["saga_id"],
        "step_name": "reserve_inventory"
    })

Duplicate saga executions on restart

If your orchestrator service restarts mid-saga, it may replay events and re-execute already-completed steps. Guard every step action with an idempotency key — see Template 3 above.

Choreography saga losing events

In a choreography-based saga, a downstream service may miss an event if it was offline when published. Use a durable message broker (Kafka with replication, RabbitMQ with persistence) and store the current saga state in a dedicated saga_log table so you can replay from the last known good step.

Timeout firing before a slow-but-valid step completes

A step like create_shipment might take up to 15 minutes during peak load but your global timeout is 5 minutes, causing spurious compensation. Make step timeouts configurable per step type — see references/advanced-patterns.md for the TimeoutSagaOrchestrator implementation and the STEP_TIMEOUTS dict pattern.

Compensation order not matching execution order

When two steps both complete before a failure is detected, compensation must run in strict reverse order or you leave data in an inconsistent state. Verify that _compensate() iterates from current_step - 1 down to 0, and add an integration test that deliberately fails at each step index to confirm correct rollback order.

Advanced Patterns

The references/ directory contains production-grade implementations not needed for most sagas:

references/advanced-patterns.md — Full SagaOrchestrator abstract base class, TimeoutSagaOrchestrator with per-step deadlines, detailed bank transfer compensating transaction chain, Prometheus instrumentation, stuck saga PromQL alerts, and DLQ recovery worker.

Related Skills

cqrs-implementation — Pair sagas with CQRS for read-model updates after each step completes
event-store-design — Store saga events in an event store for full audit trail and replay capability
workflow-orchestration-patterns — Higher-level workflow engines (Temporal, Conductor) that build on saga concepts