Home ›

Web Client Programming Using Perl

Issue 66

From Issue #66
October 1999

Oct 01, 1999  By Robb Hill
 in
Web site monitoring of your system can be easy using Linux and Perl.

Many users of Linux are initially attracted to the platform for its powerful web server capabilities. Developing a web site on the Linux platform is a very satisfying experience. After the fun of designing and developing the site is over, it moves to production. Once in production, a web site typically has uptime requirements; to ensure these are met, the site must be monitored. I use a monitoring system that requests pages from a number of web sites, several times a day. If any server does not serve a web page, it is retried. If again there is no response, I am alerted via pager. Using this system, I can respond to an outage even before a user can report a problem. It takes only a little Perl and Linux to make this happen.

Linux and Perl were the obvious choices for a web server monitoring and alerting facility. Linux provides the stability and flexibility in the platform, and Perl, using the LWP bundle of modules (also known as libwww), provides an excellent means to work with HTTP requests.

I will explain how to compile/install the components needed, how to create a simple Perl script that will “HTTP ping” a server (HTTPping.pl), how to send a page to a pager using Perl, and how to glue it all together into an industrial-strength web site monitoring solution (Monitor.pl).

LWP

The wide availability of modules that extend Perl's functionality is one of the language's strong suits. In the case of fetching web pages, there are several modules that could be used. LWP is the clear choice, because it is a fantastic set of modules giving Perl powerful control over HTTP and HTML. Before you can begin exploring LWP and how you can use it to monitor a web site, you must install it.

Table 1.

The LWP modules depend on several other modules. These may not be installed on your system. If not, they must be downloaded and installed. Table 1 contains the exact version I installed, in the order I installed them. Except for SSLeay (more on that later), you can download all these packages from CPAN (Comprehensive Perl Archive Network). If you are new to Perl, it would be a good idea to browse around CPAN for a bit. It contains an enormous number of support modules for Perl that can save a lot of programming time and costs.

Once you have downloaded the tar.gz files, they must be expanded using the tar command:

tar -zxvpf MIME-Base64-2.11.tar.gz

This will uncompress and unpack the package. Do this for all archives. When finished, you will have a directory full of the original archives and a new folder for each archive. Each folder contains the module's installer; run the installer for each package. Again, using the MIME::Base64 module as the example, change (using cd) to the HTML-Parser-2.22 directory and type the following commands: 

perl Makefile.PL
make
make test
make install
This is the typical way of installing Perl modules. However, packages vary, and you should always read the README or INSTALL file and other documentation that comes with any module.

SSLeay

If you plan to HTTP ping servers that use SSL (secure sockets layer), you must compile and install SSLeay and Crypt-SSLeay. SSLeay is a set of programs that provides the cryptographic routines needed for SSL. Crypt-SSLeay is the Perl module that serves as a wrapper for SSLeay. I suggest you read the documentation that comes with SSLeay. It will help especially if you run into any problems when compiling.

Execute the following commands in the directory to which you uncompressed the SSLeay-0.6.6b.tar.gz archive to install SSLeay:

./Configure linux-elf
make depend
make
make rehash
make test
make install

Three important things about SSLeay are:

  1. Don't try to use the newer versions of SSLeay. They will not work with Crypt-SSleay and the LWP bundle. The last stable version is SSLeay-0.6.6b.tar.gz.

  2. Second, SSLeay leaks memory. If you choose to use SSLeay and LWP to repeatedly HTTP ping a site that uses SSL, you will probably experience some problems with memory leaks. By calling HTTPping.pl from Monitor.pl, the script executes, pinging the site once, then terminates; this reduces the potential for a memory leak to accumulate, thereby causing your application to crash.

  3. Since SSLeay uses RSA, you should read the SSLeay FAQ (see references) to determine if you can legally use SSLeay and if you need a license from RSA.

______________________

Comments

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

old info

Sasha Chorny's picture
Submitted by Sasha Chorny (not verified) on Mon, 05/12/2008 - 05:29.

MIME::Base64 is core from 5.8 and in general installation is more convenient with cpan shell.

White Paper
More Resources
Fabric-Based Computing Enables Optimized Hyperscale Data Centers

Today’s modular x86 servers are compute-centric, designed as a least common denominator to support a wide range of IT workloads. Those generic, virtualized IT workloads have much different resource optimization requirements than hyperscale and cloud applications. They have resulted in a “one size fits all” enterprise IT architecture that is not optimized for a specific set of IT workloads, and especially not emerging hyperscale workloads, such as web applications, big data, and object storage. In this report, you will learn how shifting the focus from traditional compute-centric IT architectures to an innovative disaggregated fabric-based architecture can optimize and scale your data center.

Learn More

Sponsored by AMD

White Paper
More Resources
Red Hat White Paper: Using an Open Source Framework to Catch the Bad Guy

Built-in forensics, incident response, and security with Red Hat Enterprise Linux 6

Every security policy provides guidance and requirements for ensuring adequate protection of information and data, as well as high-level technical and administrative security requirements for a system in a given environment. Traditionally, providing security for a system focuses on the confidentiality of the information on it. However, protecting the data integrity and system and data availability is just as important. For example, when processing United States intelligence information, there are three attributes that require protection: confidentiality, integrity, and availability.

Learn more about catching the bad guy in this free white paper.

Learn More

Sponsored by DLT Solutions