System design interview question
Design a Distributed Workflow Orchestration Engine like Apache Airflow at Scale
Design a distributed system that orchestrates complex, multi-stage workflows (DAGs) with dependency management, fault tolerance, and dynamic task scheduling across a cluster of workers. The system must support: (1) defining workflows as directed acyclic graphs with heterogeneous task types, (2) scheduling and executing tasks with retry logic and exponential backoff, (3) managing task state transitions and handling partial failures without losing progress, (4) distributing task execution across workers with load balancing and priority queues, and (5) providing observability through audit logs and metrics collection. Key challenges include designing a pluggable task executor system that supports multiple task types (SparkJob, HTTPCall, DatabaseQuery, etc.) without creating a God object, handling distributed deadlocks when tasks depend on each other cyclically (or detecting such cases early), managing transient failures vs. permanent failures, and ensuring idempotency for task retries when side effects have already occurred.
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