Michal Szymaniak

Replication for web hosting systems

Replication is a well-known technique to improve the accessibility of Web sites. It generally offers reduced client latencies and increases a sites availability. However, applying replication techniques is not trivial, and various Content Delivery Networks (CDNs) have been created to facilitate replication for digital content providers. The success of these CDNs has triggered further research efforts into developing advanced <i>Web replica hosting systems</i>. These are systems that host the documents of a website and manage replication automatically. To identify the key issues in designing a wide-area replica hosting system, we present an architectural framework. The framework assists in characterizing different systems in a systematic manner. We categorize different research efforts and review their relative merits and demerits. As an important side-effect, this review and characterization shows that there a number of interesting research questions that have not received much attention yet, but which deserve exploration by the research community.

Enabling Service Adaptability with Versatile Anycast

We present versatile anycast, which allows a service running on a varying collection of nodes scattered over a wide‐area network to present itself to the clients as one running on a single node. Providing a single logical address enables the client‐side software to preserve the traditional service access model based on single access points. At the same time, the dynamic composition of anycast groups implemented by versatile anycast enables the server‐side service infrastructure to evolve and adapt to changing network conditions. We implement versatile anycast using Mobile IPv6, which decouples the logical addresses of mobile nodes from their physical location. We exploit that decoupling to implement logical service addresses that are not bound to any physical nodes, and employ standard MIPv6 mechanisms to dynamically map each such address onto individual service nodes. Our solution enables a service to transparently hand off clients among the service nodes at the network level while preserving optimal routing between the clients and the service nodes. We demonstrate that the overhead of versatile anycasting is very low. In particular, the client‐perceived handoff time is shown to be a linear function of the latencies among the client and the service nodes participating in the handoff. Copyright

Versatile anycasting with mobile IPv6

Anycasting was introduced to facilitate efficient communication between distributed Internet services and their clients, as it allows client requests to be automatically routed to nearby service instances. However, even though several any-cast implementations have been proposed, their various limitations prevent them from being widely adopted by large-scale distributed systems.This paper identifies the key limitations of existing anycast implementations, and proposes how to implement anycast such that all these limitations are addressed without harming the performance of anycast communication. Our solution relies on address-translation capabilities present in modern operating systems. These capabilities have originally been designed for communication with mobile nodes. However, we demonstrate that one can exploit them to implement versatile anycasting at low cost.