Introduction

One of Asia's largest budget carriers faced fragmented shopping experiences due to disjointed shopping carts siloed by lines of business (flights, hotels, rides), leading to low adoption rates, poor checkout conversions, and untapped personalization opportunities.

• Functional: Multi-LOB cart CRUD APIs (cart, /items, /summary), idempotency/locks, sliding TTL (30min guest/120min auth), rehydration (isRestored=true), events/admin endpoints.

• Non-Functional: SLOs (GET ≤50ms p99, POST ≤200ms, 99.95% availability); Otel JSON logs (traceId/cartId/userId), RED/USE dashboards, quota alerts; unit ≥80%, Testcontainers integration.

• Infra/Security: Kong Gateway OAuth2/JWT, Firestore composites/VPC, Secret Manager, Workload Identity; CI/CD, Postman collections, dev/staging readiness.

• Siloed Architecture: Disconnected systems with no unified state management or audit trails

• Tech Stack Pivot: Migration from Redis/MongoDB/PubSub to Firestore for performance and simplicity

• Evolving Scope: Mid-sprint changes (repricing removal, scope expansion) without impacting timelines

• Dependency Risks: External dependencies (LOB validators, infra provisioning, auth setup)

• Execution Complexity: Managing parallel frontend-backend development and tight delivery timelines

• Future-Ready Capabilities for bundling, orchestration, and personalization

• Universal Cart Service enabling seamless cross-LOB cart management

• Scalable Cloud-Native Architecture with real-time observability

• 20–30% increase in cart adoption and checkout conversions

 Technological Framework

Why these technologies?

Spring Boot with Kubernetes provides the production-grade reliability and scaling needed for 99.95% availability, while Firestore's document model delivers the performance and simplicity required for unified cart state management.

Why these tools?

Kong API Gateway with OAuth2/JWT enforces security and idempotency at the API layer, while Open Telemetry and Cloud Operations Suite deliver the RED/USE dashboards and end-to-end tracing required for SLO monitoring.

Why this Setup?

Per-LOB validator integrations with unified auth ensure that cart operations are validated against real-time inventory and pricing for each line of business, while CI/CD automation maintains dev/staging parity.

Takeaway

Zapcom delivered a universal cart service for a multinational low-cost airline — achieving 20–30% increase in cart adoption and checkout conversions, with future-ready capabilities for bundling and personalisation.