Scalable Web Server on Heterogeneous Clusters
Probation Report
CHEN Ge
Department of Computer Science and Information Systems
The University of Hong Kong
gechen@csis.hku.hk
Abstract
Cluster provides a viable approach to build scalable Web servers. However,
current Web server designs do not fully utilize the underlying features of the cluster and
most parallel web server designs are for homogenous cluster. In this talk, a pure-Java
parallel Web server architecture will be discussed. This Web server design aims to
achieve good scalability and high performance. To effectively utilize the whole physical
memory of a cluster, a global object space is constructed among all the cooperative Web
servers. The global object space acts as a giant object cache to shorten the Web object
access time. In addition, a global thread space is established to let all the Java threads that
are bounded to the client requests see the same objects created in the global object space.
With the support of the global thread space, our web server can fully utilize the multithreaded feature of Java to achieve better resource utilization and load balance. Java's
cross platform feature makes our approach able to run on a heterogeneous cluster to
provide different types of services.
Introduction
In order to meet the uproarious load on Web servers, Web server cluster is widely
adopted by most current research and industry projects on Web server. In current Web
server clusters, each machine in the system usually works separately. Recently, some
Web servers implemented some simple cooperative cache scheme, but it is a very simple
and naïve one that only handles the cooperative work on the caching problem of a Web
server. Limited by the hardware and software capability a single machine can provide,
these approaches can not fully utilize the benefits a cluster can provide, like giant overall
memory space, parallel computation power and distributed I/O space. Further more,
almost all current Web server cluster systems are built on homogeneous environment.
With the trends of increasing diversity of Web service demanded by Internet applications,
it is hardly able to easily provide all type of Web service in a homogeneous environment.
Java’s cross-platform makes built Web server cluster in a heterogeneous environment
possible. In this report, we proposed a pure-Java Web server that can run on a
heterogeneous cluster environment. A global object space acts as a toughly coupled
memory cache for shortening the access time. Our Web server has another global thread
space trying to fully utilize the multi-threaded feature of Java to achieve better resource
utilization and load balance by distributing load among the machines in the cluster.
Global Object Space
Current Web servers usually use some simple cache mechanism to improve the
response time of Web access. Some of them only cache object location information that
will speed up the resource look up phase of servicing a request. These systems left the
caching of file content to OS’ file systems. But research shows that file content caching
in a cluster environment can significantly improve Web server’s performance [A.L.
Narasimba Reddy]. Some research projects implemented simple cooperative schemes to
make several Web server work together. But all these approach failed to fully utilize the
underlying benefits a cluster can provide, such as giant memory space, parallel I/O
system, and so on. So, in our approach, we will construct a global object space. The
global object space aims to unify all the physical memory space in the system to provide
a giant cache space for file content caching. Meanwhile, the global object space is not
only to provide a giant object caching space, it is also aims to make all the resources in
the cluster available to every Web server in the cluster. Because the Web server is pureJava, it can run on a heterogeneous environment. Through the global object space, each
single Web server in the cluster will be able to access all the resources in the whole
system; even that resource is maybe on a different hardware or software platform.
Global Thread Space
The global thread space is to fully utilize Java’s multi-thread feature. Together
with the global object space, the global thread space will distribute incoming request
among the nodes in the cluster. The global thread space will dispatch incoming request
according the resource location. The global thread space consists of all the threads in the
system available to handle incoming requests. These threads will cooperate to serve
incoming request together, while in traditional Web server clusters, each node works
separately. The global thread space will try to explore maximum parallelism as much as
possible. When a node gets a request and parsed the requested URL partially, knowing
which thread in the global thread space to handle the request, it will hand the remaining
parse task to that thread immediately to free itself to handle next incoming request.
Scalable Heterogeneous Cluster
Because our Web server is written in pure-Java, it will be able to run on any
platform. In a homogeneous environment, the Web server is only able to provide services
that the underlying hardware and software platform can support. In our platform, the
underlying hardware and software difference is hidden by JVM. With specially designed
frames, the Web server is able to access underlying resources of different platform. Each
node can provide it platform-specific services. With the global object space, each node in
the cluster is able to access resource of other nodes in the cluster, even these nodes are of
different platforms, the JVM make the access equal to all nodes in the cluster. With such
a design, we can add new nodes of different hardware and software configuration the
cluster, while still make the whole cluster works cooperatively toughly as a single
machine.
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