Walmart Labs·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say

Jun 2026

Summary

System design round at Walmart Labs focused entirely on building a multi-carrier shipping platform. Pretty dense question with a lot of moving parts, and I felt like I was playing catch-up the whole time trying to cover everything they wanted.

Questions Asked (1)

Design a parcel shipping system that supports multiple carriers like UPS, USPS, and FedEx, covering shipment creation, carrier selection, label generation, tracking, and a unified internal API that abstracts carrier-specific differences.

System DesignAPI & IntegrationsData Modeling

Author's notes

I started with the data model because that felt safest, shipment, address, carrier, label, tracking event.

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AI HintsAI Generated

Suggested Approach

Start by clarifying functional and non-functional requirements, then design a layered architecture with a unified internal API, a carrier abstraction layer, and pluggable carrier adapters. Walk through the end-to-end flow for shipment creation, carrier selection, label generation, and tracking, highlighting how the abstraction handles carrier-specific differences.

Pro tip: Emphasize idempotency and asynchronous processing for label generation and tracking updates, as these are critical for reliability and scalability in a high-volume shipping system like Walmart's.

1. Clarify Requirements and Scope

Ask about expected volume, supported carriers, required features (e.g., rate shopping, label formats, tracking webhooks), and non-functional needs like latency, availability, and consistency.

2. Define Unified Internal API

Design a clean, carrier-agnostic API with endpoints for creating shipments, selecting carriers, generating labels, and tracking. Use standard data models for requests and responses.

3. Design Carrier Abstraction Layer

Introduce an interface that each carrier adapter implements, translating unified API calls into carrier-specific protocols (e.g., SOAP, REST, XML) and normalizing responses.

4. Detail Core Flows and Data Model

Walk through shipment creation (validate address, select carrier via rate shopping, generate label asynchronously, store shipment record) and tracking (poll or webhook, update status, notify).

5. Address Scalability, Reliability, and Extensibility

Discuss idempotency, retries, circuit breakers, caching, async processing, and how to add new carriers without changing the core system.

Key Points to Mention

Adapter pattern or strategy pattern for carrier integration
Idempotency keys for shipment creation and label generation
Asynchronous processing for label generation and tracking updates
Rate shopping and carrier selection logic (cost, speed, service level)
Unified data model for shipments, labels, and tracking events
Circuit breakers, retries, and fallback mechanisms for carrier API failures

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.