Mapping Service-Level Agreements in Distributed Applications

In a previous column, I discussed how to build distributed systems from quality-of-service (QoS)-aware software components.1 I also described a design by which individual components can engage in QoS negotiation and perform admission control so that new incoming requests don’t violate committed QoS requirements.2 But what happens in a distributed application made up of several QoS-aware components? Moreover, what if the application has a global service-level agreement (SLA) for maximum end-to-end execution time? The problem I discuss here is how to determine which SLAs should be negotiated at the component level so that the global SLA is satisfied at the minimum possible cost.