faststream-redis-timers 0.2.0

FastStream broker integration for Redis-backed distributed timer scheduling

faststream-redis-timers

faststream-redis-timers is a FastStream broker integration for Redis-backed distributed timer scheduling.

Schedule messages to be delivered to subscribers at a future point in time, with at-least-once delivery across multiple workers.

from datetime import timedelta
from faststream import FastStream
from faststream_redis_timers import TimersBroker
from redis.asyncio import Redis

client = Redis.from_url("redis://localhost:6379")
broker = TimersBroker(client)
app = FastStream(broker)

@broker.subscriber("invoices")
async def handle_invoice(invoice_id: str) -> None:
    print(f"Invoice {invoice_id} is due!")

@app.after_startup
async def schedule() -> None:
    await broker.publish(
        "INV-001",
        topic="invoices",
        activate_in=timedelta(days=30),
    )

Schedule at an absolute time with activate_at instead. publish() returns the resolved timer_id so you can keep it for cancellation:

from datetime import UTC, datetime

timer_id = await broker.publish(
    "INV-001",
    topic="invoices",
    activate_at=datetime(2026, 6, 1, 9, tzinfo=UTC),
)

How it works

Timers are stored in Redis as two keys per topic:

• A sorted set (timers_timeline:{topic}) with the activation timestamp as score
• A hash (timers_payloads:{topic}) with the serialized message body

So a timer on the invoices topic lives under timers_timeline:invoices and timers_payloads:invoices — handy when poking around in redis-cli. A TimersRouter(prefix="my-service:") extends the suffix to my-service:invoices.

A polling loop checks for due timers and atomically claims each one via a Lua script that pushes its score forward by lease_ttl seconds — granting the worker a lease. The timer is removed from Redis only after the handler completes successfully. If the worker crashes mid-handler or the handler raises, the lease eventually expires and another worker re-claims the timer.

This is the standard SQS-style visibility-timeout pattern: at-least-once delivery with no data loss on crash, at the cost of requiring idempotent handlers.

Cancellation

timer_id = await broker.publish("INV-001", topic="invoices", activate_in=timedelta(days=30))
await broker.cancel_timer("invoices", timer_id)

Tracing & headers

publish() accepts correlation_id and headers — both round-trip to the handler via the standard FastStream StreamMessage:

await broker.publish(
    {"order_id": 42},
    topic="orders",
    correlation_id="trace-abc-123",
    headers={"x-tenant": "acme", "x-priority": "high"},
)

Inside the handler:

from faststream import Context

@broker.subscriber("orders")
async def handle(
    body: dict,
    correlation_id: str = Context("message.correlation_id"),
    tenant: str = Context("message.headers.x-tenant"),
) -> None:
    ...

Connection ownership

TimersBroker does not close the Redis client you pass in — the caller owns its lifecycle. The same client can be shared across multiple brokers, so closing it from one broker would surprise the others. Manage the client with async with or a try/finally:

async with Redis.from_url("redis://localhost:6379") as client:
    broker = TimersBroker(client)
    app = FastStream(broker)
    await app.run()

Tuning

Per-subscriber knobs (passed to @broker.subscriber("topic", ...)):

• lease_ttl (default 30 seconds) — how long a worker holds the lease while processing. Handlers must complete within this window or another worker may re-deliver the timer (duplicate). Increase if your handlers are slow.
• polling_interval (default 0.05 s) — base poll interval used when the queue has work or just transitioned from idle. Doubles on each consecutive empty cycle, capped at max_polling_interval, with ±50% jitter applied each sleep.
• max_polling_interval (default 5.0 s) — ceiling for the adaptive idle backoff. Lower it for tighter delivery latency on idle queues; raise it to reduce Redis load on workloads with long idle stretches.
• max_concurrent (default 5) — maximum number of handlers running in parallel per subscriber. Also caps the fetch batch size per poll cycle. Handlers must be safe under concurrency in addition to being idempotent.

Failure modes

• Handlers must be idempotent. A handler that ran successfully but whose ack failed to land in Redis (network blip) will be retried; a handler that takes longer than lease_ttl may be re-delivered to another worker.
• Buggy handler retries forever. If a handler always raises, the timer is retried every lease_ttl seconds indefinitely — there is no built-in attempt counter. Raise faststream.exceptions.RejectMessage from your handler to drop a poison-pill timer permanently, or track attempts in your own state if you need a hard cap.

High availability

Run multiple TimersBroker processes against the same Redis keys. The Lua claim script ensures each due timer is leased by exactly one worker at a time; failover is automatic via lease expiry.

broker = TimersBroker(
    Redis.from_url("redis://..."),
    timeline_key="my_timeline",
    payloads_key="my_payloads",
)

📚 Documentation

📦 PyPi

📝 License