| Network services have been increasingly integrated into our daily lives, but their accessibility and stability are also frequently impacted by flash crowds or Denial of Service (DoS) attacks. To be immune from flash crowds or DoS attacks, robust network services must possess two important qualities: completeness and generality. Completeness implies that all resources must be protected, including CPU time, memory and disk capacity, and link bandwidth. Generality means not handling attacks or faults as extraordinary events, but instead treating them within the same framework used during normal operations. Fundamentally, this is a matter of efficient management of networked resources.; Toward this end, we use Content Distribution Networks (CDN) as an example, and investigate how request redirection impacts CDN robustness. CDN systems deploy redundant resources (servers) geographically distributed across the Internet and distribute client requests to an appropriate server based on a variety of factors—e.g., server load, network proximity, cache locality—in an effort to reduce response time and increase the system capacity under load. We explore the design space of the redirection strategies employed by request redirectors, and define a class of new algorithms that carefully balance load, locality, and proximity. We use large-scale detailed simulations to evaluate various strategies. These simulations demonstrate the effectiveness of our new algorithms, which yield a 60–91% improvement in system capacity when compared with the best published CDN technology, yet user-perceived response latency remains low and the system scales well with the number of servers. We also build a prototype CDN, named CoDeeN, on the PlanetLab testbed. CoDeeN helps us to gain experience on managing and monitoring an operational CDN, and will be used in future research.; Through this thesis, we demonstrate that the resilience of large wide area network services can be improved through efficient management of networked resources. By adapting unified resource management schemes, we present a practical way to build network systems that not only handle a larger volume of regular traffic more easily, but also absorb flash crowds and deter DoS attacks as a natural part of their operations. |
