Open-Source Web Servers: Performance on a Carrier-Class Linux Platform
ARIES (Advanced Research on Internet E-Servers) is a project that started at Ericsson Research Canada in January 2000. It aimed at finding and prototyping the necessary technology to prove the feasibility of a clustered internet server that demonstrates telecom-grade characteristics using Linux and open-source software as the base technology.
The telecom-grade requirements for clustered internet Linux servers are very strict and well recognized within the telecommunications industry. These characteristics include a combination of guaranteed availability (guaranteed 24/7 access), guaranteed response time (statistically guaranteed delays), guaranteed scalability (large-scale linear scalability) and guaranteed performance (to serve a minimum number of transactions per second).
In addition, telecom-grade internet servers have other important requirements to meet, such as the capability to cope with the explosive growth of internet traffic (growing at over 100% every six months) as well as meeting the increased quality of service demanded by the end users, not to mention very strict security levels.
These internet servers necessitate a high-performance and highly scalable web server. Since all of the work in ARIES is based on open-source software, we needed an open-source web server that could help us build our targeted system.
One of our goals in ARIES is to be able to build an internet server capable of scaling to thousands of concurrent users without download speeds noticeably slowing. This type of scalability is best accomplished when application servers are hosted on a group or cluster of servers. When a request for a particular page of a web site comes in, that request is routed to the least busy server (using a smart and efficient traffic distribution solution, either hardware- or software-based).
We decided to experiment with three web servers: Apache, Jigsaw and Tomcat. Apache is the world's most popular web server. We have been experimenting with it since ARIES first started in 2000. Jigsaw, a Java-based web server, is currently used on our experimental Linux cluster platform. Tomcat, another Java-based web server, is a potential replacement to Jigsaw if proven to be a better performer.
The Apache web server is a powerful, flexible, HTTP/1.1-compliant web server. According to Netcraft Web Servers' survey, Apache has been the most popular web server on the Internet since April 1996. This comes as no surprise because of its many characteristics, such as the ability to run on various platforms, its reliability, robustness, configurability and the fact that it provides full source code with an unrestrictive license. For our tests, we have experimented with Apache 1.3.14, which was the stable release at the time, and the Apache 2.08 alpha release (2.08a).
Jigsaw is W3C's open-source project that started in May 1996. It is a web server platform that provides a sample HTTP 1.1 implementation and a variety of other features on top of an advanced architecture implemented in Java. Jigsaw was designed to be a technology demonstration to experiment new technologies rather than a full-fledged release. For our tests, we used Jigsaw 2.0.1 (serving HTTP requests on port 8001) in conjunction with the Java 2 SDK.
Tomcat is the reference implementation for the Java Servlet 2.2 and JavaServer Pages 1.1 technologies. Tomcat, developed under the Apache license, is a servlet container, a runtime shell that manages and invokes servlets on behalf of users, with a JSP environment.
Tomcat can be used either as a standalone server or as an add-on to an existing web server such as Apache. For our testing, we installed Tomcat 3.1 as a standalone server, servicing requests on port 8080.
For the purpose of testing and evaluating the above-mentioned web servers, we set up a typical Ericsson Research Linux cluster platform (see Figure 1).
This platform is targeted for carrier-class server applications. The testing environment consisted of:
Eight diskless Pentium III CompactPCI CPU cards running at 500MHz and powered with 512MB of RAM. The CPUs have two onboard Ethernet ports and are paired with a four-port ZNYX Ethernet card providing a high level of network availability.
Eight CPUs with the same configuration as the others except that each of these CPUs has a disk bank. The disk bank consists of three 18GB SCSI disks configured with RAID 1 and RAID 5 to provide high data availability.
Master Nodes: two of the CPUs (with disks) act as redundant NFS, NTP, DHCP and TFTP servers for the other CPUs. The code for NFS redundancy was developed internally along with a special mount program to allow the mounting of two NFS servers at the same mounting point.
When we start the CPUs, they boot from LAN (either LAN 1 or LAN 2 for higher availability in case either of the LANs go down). Then they broadcast a DHCP request to all addresses on the network. The master nodes will reply with a DHCP offer and will send the CPUs the information they need to configure network settings such as the IP addresses (one for each interface: eth0, eth1, znb0 and znb1), gateway, netmask, domain name, the IP addresses of the boot servers and the name of the boot file.
The diskless CPUs will then download and boot the specified boot file in the DHCP configuration file, which is a kernel image located under the /tftpboot directory on the DHCP server. Next, the CPUs will download a RAM disk and start the application servers, which are the Apache, Jigsaw and Tomcat web servers. The process of booting a diskless server takes less than one minute from the time it is booted until we get the login prompt.
As for the CPUs with disks, they will download and boot the specified boot file in the DHCP configuration file, which is a kernel image located under the /tftpboot directory on the DHCP server. Next, they will perform an automatic RAID setup and a customized install for Red Hat 6.2. When the CPUs are up, they will start Apache, Jigsaw and Tomcat web servers, each on a different port. The process of booting a disk server takes around five minutes from the time it is booted until we get the login prompt (which includes an automatic RAID 1 and RAID 5 setup, as well as a complete install from scratch for Red Hat 6.2).
For our testing, we were booting the disk CPUs (six of them, except the master nodes) as diskless CPUs so we could have an identical setup on many CPUs.
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