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Internet servers need t o b e highly-available, inexpensive, and scalable. These goals are often con icting and most designs meet, with limited success, only few of them.In this paper we describe the SunSCALR framework that achieves these goals by combining proven technologies, careful system design, and engineering trade-o s. It uses a distributed, self-stabilizing algorithm for status monitoring and failure detection, and IP failover for automatic recon guration. SunSCALR provides high-availability against message loss, host crashes, and scheduled downtime, and allows on-the-y addition and removal of hosts.We present detailed performance of SunSCALR. It can provide 10 second failover latency i.e., better than 99.999 availability if machines fail for 2 hours month. SunSCALR based p r oducts have been in use within Sun and are also available in the market.

Two specific problems faced in large distributed systems are (1) evolving and managing different versions of an interface while minimizing the impact on existing clients, and (2) supporting the addition of auxiliary interfaces that are orthogonal to the main interface of an abstraction.In the context of the Spring distributed system, we addressed both problems using an object-oriented interface definition language. Different versions of an interface are represented as different types with an inheritance relationship that minimizes the impact on existing clients and allows easy management of versions.We distinguish between fundamental and auxiliary properties each of which are defined as separate types. Rather than use simple root inheritance, we use a combination of root and leaf inheritance. This provides flexibility in supporting auxiliary properties and allows us to add new auxiliary properties as the system evolves without forcing the system to be recompiled.The solutions have been tested and refined through their use in the Spring system.