A system can host APIs for a plurality of different tenants and receive requests from many different client devices. As requests are received, an associated tenant can be identified, and a router can determine if a container instance is available to service the request. A container instance may be an empty container instance including an internal endpoint, a Web server, and a runtime environment. An empty container instance can be unassociated with a particular tenant. To associate a container instance with a tenant, a data store, such as a key-value data store can retrieve configuration files that turn the agnostic container instance into a container instance that is associated with particular tenant and includes configuration code to perform the requisite API functions. The pool of empty and populated containers can be managed efficiently.