We propose service continuations (SC), an operating system mechanism that supports seamless dynamic migration of Internet service sessions between cooperating multiprocess servers. Service continuations provide a server application with a simple and easy to use abstraction, and a means to migrate the service state along with the serviced connection. SC supports transparent resumption of service to the client at another server, and guarantees integrity and consistency of communication channels used by server processes. SC is a generic, application independent-mechanism that can be used to provide service continuity and availability for today?s complex Internet services.

We have implemented SC in FreeBSD and used them successfully in three real servers: the Apache web server, the PostgreSQL transactional database server, and the Ice-cast streaming server. We present results of an experimental evaluation showing that using SC adds negligible run-time overhead to existing servers and that SC enables efficient dynamic migration of client sessions.