Waiter is an open-source platform for running and automatically managing the lifecycle of HTTP services. It is a distributed system that sits between services and clients, launching and scaling services as necessary, ensuring health and uptime. Waiter provides a simplified interface for service descriptions, request-based auto-scaling, run-as-requestor services, and consumer-controlled service versioning. Two Sigma has used Waiter in production since 2015, and released Waiter on GitHub in February 2017. Hundreds of HTTP services at Two Sigma are run via Waiter, servicing hundreds of millions of HTTP requests on a daily basis. Until recently, Waiter has delegated much of its low-level scheduling and service-management operations to Mesos+Marathon. However, the addition of Kubernetes clusters as a resource available to all engineers at Two Sigma has motivated support for Kubernetes as an alternative backend service-management platform in Waiter.