rq-rediscron 0.1.5

Redis-backed runtime-editable cron scheduler for RQ

rq-rediscron provides Redis-backed subclasses for RQ cron scheduling:

• RedisCronJob

• RedisCronScheduler

Cron job definitions are stored in Redis hashes and indexed in a sorted set by next enqueue time. This lets scheduler processes pick up job creates, edits, and deletes at runtime without restart.

Only one RedisCronScheduler process runs at a time. The scheduler acquires rq:cron_jobs:lock during register_birth(), extends that lock on heartbeat, and releases it during register_death(). A second scheduler can start after the lock TTL expires, which provides failover without duplicate enqueue loops.

Usage

from redis import Redis
from rediscron import RedisCronScheduler


def rebuild_metric(metric_id: str) -> None:
    ...


connection = Redis.from_url("redis://localhost:6379/0")
scheduler = RedisCronScheduler(connection)
scheduler.register(
    rebuild_metric,
    queue_name="metrics",
    id="metric:pm25",
    args=("pm25",),
    interval=300,
)
scheduler.start()

Redis keys

Keys used by this package:

• rq:cron_job:{id} stores one cron job hash.

• rq:cron_jobs indexes job ids by next enqueue timestamp.

• rq:cron_jobs:lock allows one live scheduler process at a time.

• rq:cron_jobs:last_update records runtime changes.

• rq:cron_jobs:events publishes create, update, and delete events.

Why?

The original cron implementation in RQ is holding all the cron jobs locally as a list inside the instance of the scheduler. Because of this design choice, as soon as the scheduler is started, the list of scheduled jobs cannot be easily modified.

In some cases, we want to be able to add/edit/delete scheduled jobs on the fly and for the scheduler to acknowledge those events accordingly. This is what lead the design choices for this package.