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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Heartbeat script in Perl

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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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
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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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