Staff Backend Engineer

Company Introduction We exist to wow our customers. We know we’re doing the right thing when we hear our customers say, “How did I ever live without Coupang?” Born out of an obsession to make shopping, eating, and living easier than ever, we’re collectively disrupting the multi-billion-dollar e-commerce industry from the ground up. We are one of the fastest-growing e-commerce companies that established an unparalleled reputation for being a dominant and reliable force in South Korean commerce. We are proud to have the best of both worlds — a startup culture with the resources of a large global public company. This fuels us to continue our growth and launch new services at the speed we have been since our inception. We are all entrepreneurs surrounded by opportunities to drive new initiatives and innovations. At our core, we are bold and ambitious people that like to get our hands dirty and make a hands-on impact. At Coupang, you will see yourself, your colleagues, your team, and the company grow every day. Our mission to build the future of commerce is real. We push the boundaries of what’s possible to solve problems and break traditional trade-offs. Join Coupang now to create an epic experience in this always-on, high-tech, and hyper-connected world. Role Overview Fulfilment Optimization (FO) owns the systems that decide how every Coupang order is planned, distributed, and fulfilled. Our Tier-1 services sit on the critical path of Coupang's ecommerce order flow — processing every order in real time across Korea and Taiwan. We operate multiple interconnected platform components: -Business Engine — Core order planning and distribution orchestrator (Kotlin/Spring Boot). Runs 5 distinct pipelines (Domestic, Cross-Market, 3PL, PDD, Replan) using a hexagonal architecture with pluggable processors, pruners, and manifest-based orchestration. -Planner Solver — Mixed-Integer Programming (MIP) optimization engine (Python/CPLEX) that minimizes total fulfilment cost across inventory, capacity, network, and delivery-promise constraints with sub-second latency requirements. -Network Manager — Manages fulfilment network topology, transportation cost, FC capacity, middle-mile logistics, and cross-FC consolidation (CFCC) across 90+ REST/gRPC endpoints. -FO Inventory — Real-time inventory availability, allocation, SKU management, and event-driven sync across multiple upstream sources (Kafka, Cassandra, Elasticsearch, Redis). -WMS Fulfilment — Order distribution, inventory allocation, fulfilment centre orchestration, shipment, delivery, and outbound management (Java/Spring, 138+ domain subpackages, Drools rules engine). -Online Simulation — Real-time simulation platform for testing planning changes against production-like order streams. -FO Workflows — Temporal-based workflow orchestration for long-running fulfilment processes. The Role We are looking for a Staff Engineer who can operate across deep implementation and broad architecture. You will help us enable the 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 system…