How do I approach System Design interview questions?

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

What difficulty level is this interview question?

This is a medium difficulty System Design question, commonly asked during Technical Screen rounds at Nash AI.

What role is this question designed for?

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

Design real-time delivery tracking with async updates

Quick Overview

This question evaluates designing scalable, fault-tolerant real-time delivery tracking systems, focusing on asynchronous event processing, out-of-order and duplicate event handling, state reconciliation, ordering and idempotency strategies, and observability.

Scenario

Design a scalable, fault-tolerant backend system to track deliveries in real time.

Context

Your company provides a tracking platform.
Third-party delivery providers (3P) perform the actual delivery and emit events (e.g., accepted, picked up, in transit, delivered, failed).
Users/clients need to:
1. Query the latest delivery status (low latency).
2. Optionally subscribe to real-time updates (e.g., WebSocket/SSE/push).

Core requirement (most important)

Handle asynchronous task execution and ensure correct state updates + queries even with:

Out-of-order events
Duplicate events (at-least-once delivery)
Provider downtime and retries
Partial failures and regional outages

Deliverables

Propose an architecture and explain:

APIs (ingest events, query status, subscriptions)
Data model (deliveries, events, status timeline)
How you process events asynchronously and update the “current status”
Ordering/idempotency strategy
Fault tolerance, scaling, and observability
Tradeoffs (consistency vs availability, storage choices)