Heartbeat script in Perl

For 2023 - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

Scenario ... an Apache httpd web server is distributing requests around between a number of Apache Tomcat instances on different computers (perhaps using mod_rewrite to allocate the requests). If a Tomcat instance become unavailable (i.e. if the host running it is taken offline) then it's to be removed from the pool, and if it comes back on line it's to be added to the pool again.

Sound complex? The basis can be quite a simple Perl script such as the one we wrote during today's course - source code here.

A regular ping around the machines that may be in the pool establishes which are present, and if the availabiity has changed the RewriteMap is rewritten. Place a pause of a few seconds into the loop and try again ....
(written 2007-02-09)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

P224 - Perl - Intersystem Communications
  [604] Perl - multiprocess applications - (2006-02-13)
  [1918] Perl Socket Programming Examples - (2008-12-02)
  [2402] Automated Browsing in Perl - (2009-09-11)
  [2695] TCP v UDP / Client v Server - Python examples - (2010-03-25)
  [2876] Different perl examples - some corners I rarely explore - (2010-07-18)
  [2970] Perl - doing several things at the same time - (2010-09-25)

A163 - Web Application Deployment - Network Configuration and Security
  [11] A bolt of lightning on Multicasting - (2004-08-11)
  [37] Security and Safety - (2004-09-03)
  [267] Searching security holes - (2005-04-04)
  [332] Looking up IP addresses - (2005-06-01)
  [506] What are DHCP and DNS? - (2005-11-27)
  [511] Domain Forwarding - 2 ways of doing it - (2005-11-29)
  [1408] Wireless hotel tips - FTP and Skype connections failing - (2007-10-26)
  [1666] Slow boot and terminal start on Linux boxes - (2008-06-05)
  [1712] As different as night and tyres - (2008-07-18)
  [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23)
  [2052] How was my web site compromised? - (2009-02-24)
  [2489] Parallel Pinging, using Python Threads or Expect spawn lists - (2009-11-02)
  [3448] Checking all the systems on a subnet, using Expect and Tk - (2011-09-18)
  [4134] Setting up your MacBook Air as a mobile broadband router - (2013-07-07)

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Java beans and classes, .war and .jar files

Some other Articles

In answer to 'am I glad I started a blog' ...
Save the Train - an update
I'm not the father
Java beans and classes, .war and .jar files
Heartbeat script in Perl
Well House Manor in the Snow
Making a mountain out of a molehill
Java Deployment course - lunch break
Rail trouble forced me to buy hotel
ls -l report, Linux / Unix - types and permssions

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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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