Distributed Locks with Redis Redlock

We needed exclusive access to reconcile batch jobs across pods. Mutex in memory does not work with horizontal scale.

Single-Instance Lock

var acquired = await db.StringSetAsync(
    lockKey, lockToken, expiry: TimeSpan.FromSeconds(30),
    when: When.NotExists);

Works until Redis fails over or clock skew causes double acquisition.

Redlock (Multi-Master)

Acquire on N independent Redis nodes. Quorum required. More resilient, more complex, debated in the community (Martin Kleppmann’s critique is worth reading).

Our Choice

Use case	Lock mechanism
Cache rebuild	Single Redis SET NX
Batch reconciliation	PostgreSQL pg_advisory_lock
Payment idempotency	DB unique constraint

Money paths use the database. Redis locks are for best-effort exclusivity where duplicate work is annoying but not catastrophic.