Design high-throughput event subscription system

Q: Design high-throughput event subscription system

This question evaluates a candidate's ability to design scalable, fault-tolerant event ingestion and subscription architectures, covering distributed systems, high-throughput messaging, content-based filtering, multi-tenant isolation, API/webhook design, delivery semantics, backpressure, sharding, security, and operational observability.

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System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Technical Screen rounds at Google.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Google during technical interviews.

Question

Design an Event Ingestion and Subscription System

Context

You are asked to design a horizontally scalable platform where producers send high-volume events (fire-and-forget, up to 1,000,000 events/second). Consumers register content-based subscription rules and webhooks to receive matching events.

Assume events are JSON objects with a tenant_id and metadata (id, timestamp, type). The system must isolate tenants and provide durable, reliable delivery to subscribers.

Requirements

Event producers
- Fire-and-forget ingestion of JSON events.
- Up to 1M events/sec sustained, with burst tolerance.
Subscribers
- Register subscription rules (content-based filtering) and webhook endpoints to receive matching events.
Define the following:
- Rule expression language (syntax, supported operators, limits).
- Registration APIs for subscriptions and webhook config.
- Webhook delivery protocol, including retries, exponential backoff, idempotency, and error handling.
- Ordering and filtering guarantees.
- Backpressure strategy for slow webhooks and overloaded tenants.
- Sharding and scalability strategy across services and storage.
- Multi-tenant isolation, rate limiting, and quotas.
- Security: authentication, authorization, encryption, data isolation, and webhook verification.
Non-functional targets (state clearly in your design):
- Durability guarantees.
- Delivery semantics (at-least-once vs exactly-once).
- Latency SLOs (ingest to delivery).
- Operational observability and failure handling.

Design high-throughput event subscription system

Quick Overview

Design an Event Ingestion and Subscription System

Context

Requirements

Solution

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