A company plans to lift-and-shift its legacy accounting application to the cloud but continue managing the operating system. Which service model should they choose?

IaaS (Infrastructure as a Service) is the correct choice because it provides the underlying infrastructure (virtual machines, storage, networking) while allowing the customer to manage the operating system, applications, and data. This aligns perfectly with a "lift-and-shift" strategy where an existing application is moved to the cloud with minimal changes, and the company wants to retain control over the OS. SaaS (Software as a Service) would mean the vendor manages everything, including the application and OS, which doesn't fit the requirement to manage the OS. PaaS (Platform as a Service) provides a development and deployment environment, abstracting the OS, which also doesn't allow for OS management by the customer. DRaaS (Disaster Recovery as a Service) is a specific use case for disaster recovery, not a general compute service model.