Senior Staff Backend Engineer

We are looking for a Senior Staff Engineer who can operate across deep implementation and broad architecture. You will set the technical direction for Tier-1 fulfilment systems, write and review production code, design systems that scale under heavy ecommerce traffic, and raise the engineering bar across the organization. The engineer in this role will directly influence how millions of orders are fulfilled every day. Every architectural decision — solver latency, pruning strategy, network cost calculation, inventory allocation algorithm impacts customer delivery promise, fulfilment cost, and operational efficiency across Coupang's entire ecommerce platform in Korea and Taiwan. This is a rare opportunity to work at the intersection of large-scale distributed systems, real-time optimization, and ecommerce fulfilment — with direct, measurable business impact. What You Will Do -Design and build scalable, reliable Tier-1 services for order planning, fulfilment optimization, inventory allocation, and network cost management — systems that process every Coupang order in real time. -Own architecture across distributed systems involving gRPC service meshes, Kafka event pipelines, CPLEX optimization solvers, multi-layer caching (Redis, S3-backed Loadable Stores), and multi-region deployments. -Write production code in Kotlin and Java and set the bar for correctness, performance, and operational safety across the team. -Lead design and code reviews — identify correctness issues, scalability risks, and operational gaps in systems handling latency-sensitive order flows (sub-second solver deadlines, P99 monitoring with 3-5s alert thresholds). -Drive reliability for mission-critical services — circuit breakers, graceful degradation (hard/soft pruners with fallback), observability, and incident prevention. -Partner with Product, Data Science, and Operations to translate fulfilment optimization goals into technical execution — PDD rationalization, CFCC (Cross-FC Consolidation), CFlow transport planning, inventory group management, and solver model improvements. -Mentor engineers and create durable technical mechanisms (pipeline patterns, adapter abstractions, feature flag discipline) that scale beyond individual projects Basic Qualifications -Proven experience designing and operating high-scale distributed systems with strict latency and reliability requirements -Excellent hands-on coding ability in Kotlin or Java (backend systems at scale) -Deep understanding of system design — API design, concurrency, data modelling, caching strategies, messaging, service-to-service communication (gRPC, REST) -Strong code review skills — ability to identify subtle correctness, performance, and reliability issues in complex codebases -Experience with production-grade systems handling high QPS, large data volumes, or Tier-1 SLAs -Experience with event-driven architectures using Kafka at scale -Experience with multi-region systems — region-specific routing, data isolation, cross-border fulfilment -Experience with resilience engineering — circuit breakers, retry strategies, load testing, capacity planning, graceful degradation patterns -Track record of technical leadership — setting architecture direction, driving cross-team alignment, mentoring senior engineers Preferred Qualifications -Experience in ecommerce, fulfilment, supply chain, logistics, inventory, order management, or planning systems -Experience with optimization systems — solvers (CPLEX, OR-Tools), decision engines, constraint programming, or data-science-integrated production systems -Experience with Agentic AI tools for development and code review — using AI-assisted coding agents (e.g., Cursor, Copilot, Devin, Claude Code) to accelerate development velocity, improve code review quality, and automate repetitive engineering tasks -Experience with Spec-Driven Development — defining system behaviour through specifications (OpenAPI/Swagger, Protocol Buffers, API-first design, contract-first development) before implementation, ensuring well-defined contracts between services Type of work model Hybrid Details to consider Those eligible for employment protection (recipients of veteran’s benefits, the disabled, etc.) may receive preferential treatment for employment in accordance with applicable laws. Privacy Notice Your personal information will be collected and managed by Coupang as stated in the Application Privacy Notice located below. https://privacy.coupang.com/en/land/jobs/