Design a Workflow Automation Platform (iPaaS)

Problem

Design Zapier's platform: run millions of automation workflows triggered by app events or polling, reliably and at scale.

Requirements

Functional:

• Trigger via webhooks or polling many apps
• Execute multi-step workflows with retries
• Per-account usage metering and limits
• Guarantee each trigger runs its actions

Non-functional:

• Millions of zaps, huge event volume
• At-least-once execution; idempotent actions
• Fair multi-tenant scheduling

Discussion points

1. Ingestion: webhooks + polling schedulers
2. Durable task queue and workers
3. Idempotency and retry/backoff for actions
4. Usage metering and rate limits per account
5. Isolation and back-pressure