This question evaluates understanding of scalable resource-allocation and matching systems, encompassing data-structure and index design, availability tracking, fragmentation minimization, concurrency control, and failure handling for large node pools.
Design a service to manage a large pool (about 100, 000) of server nodes. Each node can satisfy multiple instance types; clients call getServer(reqNumOfServer, instanceTypes[]) to request servers that collectively meet the requested types, and returnServer(ids[]) to release them. Propose data structures and indexes for fast matching, availability tracking, fragmentation minimization, and scaling. Address concurrency, starvation, and failure handling.