Service Composition: Breakout Session Summary Randy Katz David Culler Summary: Bhaskaran Raman

Discussion topics Background –Emerging Internet service model –Confederated vs. Overlay model Issues: –Granularity of composition –Growth trends: copious bandwidth –Service economics

Background Emerging Internet service model –Structure-less cloud  Structured, with Internet data centers –Portal service built out of pieces Portal  Appln infra service  Appln specific servers  Overlay networks  Physical topology Confederated vs. Overlay model –At the network layer –At the service layer

Granularity of services Heavy-weight pieces –E.g., search engines Light-weight pieces –E.g., transformation agents Yahoo portal is an example of heavy-weight composition Ninja paths: light-weight composition

Composition: beyond functionality Service composition: flexibile Can a composed service be robust? –Can we build in a negative feedback loop into the system? –With an event queue based approach to composition? –Can such a mechanism work across machines, across the network? How to compute reliability of a composed service? –Who to blame when something breaks? –SLAs for services: complex Yahoo/Google have legal SLA document

Design for decomposition Design for decomposition: how to design a service so that it can be built from pieces meaningfully End-2-End argument in service composition: –If we want to have admission control at the end, how to effect this when the bottleneck is in the middle? How to design protocols to allow for composition? –Expose more information –E.g., HTTP/1.0 has little support for caches, HTTP/1.1 has a lot of support

Internet Growth Trends Optical technology being deployed in a big way –1.6 Tb/s – 24 Tb/s in the backbone Where to place services, and how many service instances? –Does it matter, if backbone bandwidth is free and infinite? –What about the people cost of managing distributed instances? In storage management, people cost is 3-4 times more than system cost Network access cost dropping: can buy optical link for $2K a month

Service distribution vs. Centralization Might depend on granularity –Hard to distribute search engine –Easier to distribute Akamai servers: soft-state People cost: –HP: 50,000 node computer network –$10K per server –One person can manage 10 servers Service in the telephone network are distributed –Might be related to the way the telephone network evolved, and its architecture

Service distribution vs. Centralization Latency/server-load might be a reason to distribute a service –There are congested parts of the Internet today Trans-oceanic links Public-peering points Distribution: –Over-provisioning may be easier if there are many sites

Service Economics Composition: economics meets engineering SLAs are an important part Trust relations Management tools for services –What are the ones required for composed services –Diagnose and isolate problems Composition by user (dynamic) vs. composition by service providers (less dynamic)