Modular TCP Handoff Design in STREAMS-Based TCP/IP Implementation

Content-aware request processing enables the intelligent routing and request processing inside the cluster to provide the quality of service requirements for different types of content and to improve overall cluster performance.

STREAMS-based TCP/IP implementation in HP-UX 11.0 provides a convenient framework to design a library of new STREAMS modules to support content-aware request distribution and differentiation inside a cluster. Proposed modules take into account specifics of different cluster architectures and workload characteristics. These modules are designed as dynamically loadable modules and no changes are made to the existing TCP/IP code.

The proposed design has the following advantages: flexibility - new modules may be loaded and unloaded dynamically, without node function interruption; modularity - proposed modules may be ported to other OSes with minimal effort. More importantly, the proposed STREAMS modules can be easily integrated and deployed into commercial OS systems, so the end users may take advantage of these solutions much sooner.

Related Papers and Reports

• W. Tang, L. Cherkasova, L. Russell, M.W. Mutka: Modular TCP Handoff Design in STREAMS-Based TCP/IP Implementation. Lecture Notes in Computer Science, Springer-Verlag, vol. 2094, pp. 71-80, In Proceedings of the First International Conference on Networking (ICN-2001), Colmar, France, July 9-13, 2001.

• W. Tang, L. Cherkasova, L. Russell, M.W. Mutka: Customized Library of Modules for STREAMS-based TCP/IP Implementation to Support Content-Aware Request Processing for Web Applications In Proceedings of the Third International Workshop on Advanced issues of E-Commerce and Web-Based Information Systems (WECWIS'01), San Jose, June 20-21, 2001, p.202-211.
  Also HP Laboratories Report No. HPL-2001-150 , 2001.

WARD: Workload-Aware Requests Distribution

In this work, we consider a web cluster in which the content-aware distribution is performed by each of the node in a web cluster. Each server in the cluster may forward a request to another node based on the requested content.

We propose a new Workload-Aware Request Distribution strategy WARD, that assigns a small set of most frequent files, called core, to be served locally, by any server in a cluster, while partitioning the rest of the files to be served by different cluster nodes. We propose an algorithm, called ward-analysis, to compute the nearly optimal core size. The algorithm takes into account workload access patterns and cluster parameters such as number of nodes, node RAM, TCP handoff overhead, and disk access overhead.

Our simulations driven by a realistic workload show that WARD achieves super-linear speedup with increased cluster size. It shows superior performance compared with traditional round-robin strategy (up to 260% increased throughput for a cluster of 16 nodes), and outperforms a pure partitioning strategy based on a cache-affinity requests distribution (up to 50% increased throughput for a cluster of 16 nodes).

Related Papers and Reports

• L. Cherkasova, M. Karlsson: Scalable Web Server Cluster Design with WARD. In Proceedings of the Third International Workshop on Advanced issues of E-Commerce and Web-Based Information Systems (WECWIS'01), San Jose, June 20-21, 2001, pp.212-221.
  Also HP Laboratories Report No. HPL-2001-2R1 , 2001.

FLEX: Load Balancing and Management Mechanism for an Efficient Web Hosting Service

Demand for Web hosting and e-commerce services continues to grow at a rapid pace. The shared hosting market targets small and medium size businesses. The most common purpose of a shared hosting Web site is marketing. In this case, many different sites are hosted on the same hardware. A shared Web hosting service creates a set of virtual servers on the same server. Web server farms and clusters (with replicated disk content or shared file system) are used in Web hosting infrastructures for scalability and availability. In these architectures, each web server has the access to all the content.

Traditional load balancing solutions try to distribute requests uniformly across all nodes regardless of the content. This interferes with efficient use of RAM in the cluster. The popular files tend to occupy RAM space in all the nodes. This redundant replication of content across the RAM of all the nodes leaves much less RAM available for the rest of the content, leading to a worse overall system performance.

A better approach would be to partition the content among the machines thus avoiding replication of the documents in the RAMs. However, static partitioning will inevitably lead to an inefficient and inflexible solution, since the access patterns tend to vary over time, and static partitioning does not accommodate for this.

The observations above have led to the design of ``locality aware'' balancing strategies [LARD] which aim to avoid unnecessary document replication across the RAM's of the nodes to improve the overall performance of the system. These are also known as content based routing strategies.

In this work, we promote a new scalable, ``locality aware'' solution FLEX [C99] for load balancing and management of an efficient Web hosting service. The goal of FLEX is to assign sites to the nodes in the cluster to achieve both load balancing and efficient memory usage. We use the working set sizes and access rates of sites as a metric for judging their memory and load requirements.

The main attractions of the FLEX approach are ease of deployment and an extremely attractive cost/performance tradeoff. This solution requires no special hardware support or protocol changes. There is no single front end routing component. Such a component can easily become a bottleneck, especially if content based routing requires it to do such things as tcp connection hand-offs etc. FLEX can be easily implemented on top of the current infrastructure used by Web hosting service providers.

Related Papers and Reports

• L. Cherkasova, Shankar Ponnekanti: Optimizing a ``Content-Aware'' Load Balancing Strategy for Shared Web Hosting Service. In Proceedings of the Eighth International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS'2000).
  Also HP Laboratories Report No. HPL-2000-27 , 2000.

• L. Cherkasova, M. DeSouza, S. Ponnekanti. ``Performance Analysis of ``Content-Aware'' Load Balancing Strategy FLEX: Two Case Studies''. In Proceedings of Thirty-Fourth Hawaii International Conference on System Sciences (HICSS-34), Software Technology Track, January 3-6, 2001.
  Also HP Laboratories Report No. HPL-2000-28 , 2000.

• L.Cherkasova: FLEX: Load Balancing and Management Strategy for Scalable Web Hosting Service. In Proceedings of the Fifth International Symposium on Computers and Communications (ISCC'00), Antibes, France, July 3-7, 2000, p.8-13.
  Also HP Laboratories Report No. HPL-1999-64R1 , 1999.

• L. Cherkasova, Mohan DeSouza, Shankar Ponnekanti: Improving Performance of Shared Web Hosting Service on a Web Server Cluster. Poster, WWW9, Amsterdam, The Netherlands, May 16-19, 2000.

• L. Cherkasova: Scalable Web Hosting Service. HP Laboratories Report No. HPL-1999-52R1, April, 1999.