This paper studies the problem of load-balancing the demand for content in a peer-to-peer network across heterogeneous peer nodes that hold replicas of the content. Previous decentralized load balancing techniques in distributed systems base their decisions on periodic updates containing information about load or available capacity observed at the serving entities. We show that these techniques do not work well in the peer-to-peer context; either they do not address peer node heterogeneity, or they suffer from significant load oscillations. We propose a new decentralized algorithm, Max-Cap, based on the maximum inherent capacities of the replica nodes and show that unlike previous algorithms, it is not tied to the timeliness or frequency of updates. Yet, Max-Cap can handle the heterogeneity of a peer-to-peer environment without suffering from load oscillations.
Another well-studied load-balancing cluster approach is to have heavily loaded servers handoff requests they receive to other servers within the cluster that are less loaded or to have lightly loaded servers attempt to get tasks from heavily loaded servers (e.g., @cite_9 @cite_10 ). This can be achieved through techniques such as HTTP redirection (e.g., @cite_32 @cite_31 @cite_36 ) or packet header rewriting (e.g., @cite_24 ) or remote script execution @cite_43 . HTTP redirection adds additional client round-trip latency for every rescheduled request. TCP IP hand-off and packet header rewriting require changes in the OS kernel or network interface drivers. Remote script execution requires trust between the serving entities.
@cite_36 @cite_9 @cite_32 @cite_24 @cite_43 @cite_31 @cite_10
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Users of highly popular Web sites may experience long delays when accessing information. Upgrading content site infrastructure from a single node to a locally distributed Web cluster composed by multiple server nodes provides limited relief, because the cluster wide-area connectivity may become the bottleneck. A better solution is to distribute Web clusters over the Internet by placing content nodes in strategic locations. A geographically distributed architecture where the Domain Name System (DNS) servers evaluate network proximity and users are served from the closest cluster reduces network impact on response time. On the other hand, serving closest requests only may cause unbalanced servers and may increase system impact on response time. To achieve a scalable Web system, we propose to integrate DNS proximity scheduling with an HTTP request redirection mechanism that any Web server can activate. We demonstrate through simulation experiments that this further dispatching mechanism augments the percentage of requests with guaranteed response time, thereby enhancing the Quality of Service of geographically distributed Web sites. However, HTTP request redirection should be used selectively because the additional round-trip increases network impact on latency time experienced by users. As a further contribution, this paper proposes and compares various mechanisms to limit reassignments with no negative consequences on load balancing. Load balancing plays an important role in improving scalability and stability in Content Delivery Networks (CDNs) to meet the increasing demand on bandwidth. This paper proposed a modified algorithm that takes into account the equilibrium between load balancing and redirection proximity. We extended a fluid queue model which is adopted in the existing literatures to the overall CDN system. In the system, scheduler selects proper replica server for each redistributed request by exploiting load differences between them. Furthermore, through limiting the migration distance for each request, the total costs mainly associated with delay are also effectively optimized. The simulation result indicates that the proposed algorithm can efficiently reduce redirection cost compared to Control-Law Balancing (CLB) algorithm at the expense of a bit of performance sacrifice of queue balancing. Besides, we found that the proposed mechanism has more benefit on queue balancing than CLB algorithm as well, when selecting an appropriate distance threshold. Replication of information among multiple World Wide Web servers is necessary to support high request rates to popular Web sites. A clustered Web server organization is preferable to multiple independent mirrored servers because it maintains a single interface to the users and has the potential to be more scalable, fault-tolerant and better load-balanced. In this paper, we propose a Web cluster architecture in which the Domain Name System (DNS) server, which dispatches the user requests among the servers through the URL name to the IP address mapping mechanism, is integrated with a redirection request mechanism based on HTTP. This should alleviate the side-effect of caching the IP address mapping at intermediate name servers. We compare many alternative mechanisms, including synchronous vs. asynchronous activation and centralized vs. distributed decisions on redirection. Moreover, we analyze the reassignment of entire domains or individual client requests, different types of status information and different server selection policies for redirecting requests. Our results show that the combination of centralized and distributed dispatching policies allows the Web server cluster to handle high load skews in the WWW environment. Load balancing for distributed servers is a common issue in many applications and has been extensively studied. Several distributed load balancing schemes have been proposed that proactively route individual requests to appropriate servers to best balance the load and shorten request response time. These schemes do not require a centralized load balancer. Instead, each server is responsible for determining, for each request it receives from a client, to which server in the pool the request should be forwarded for processing. We propose a new request routing scheme that is more scalable to increasing number of servers and request load than the existing schemes. The method combines random server selection and next-neighbor load sharing techniques that together prevent the staleness of load information from building up when the number of servers increases. Our simulation shows that it outperforms existing schemes under a piggyback-based load update model.