Async Task Scheduler

Designed a distributed task scheduling system handling millions of delayed/recurring tasks. Supports exponential backoff retries, dead-letter queues for failed tasks, and pluggable storage backends. Tasks are stored durably and processed by worker pools with automatic scaling. Handles temporal queries efficiently using time-bucketed indexes. Provides strong guarantees: at-least-once delivery with idempotency support, preventing duplicate execution.

The scheduler uses hierarchical queuing—immediate tasks run first, then delayed tasks when their time arrives. Worker pools fetch batches of tasks and process concurrently. Persistent state enables recovery from crashes. Monitoring dashboards track task latency, failure rates, and queue depth for visibility into system health.