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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.
Handling failures / absences of your backend server nicely

It's good for your website to put a professional smile on it's face, even when it's having problems with its backend!

On high traffic sites (for example - TV show and news sites), backend servers can occasionally get overloaded and you'll want your web site visitor to get a message to that effect, rather than a failure. If the feed is a regular news feed, you might even be able to respond with the latest (cached) news if it's less that a few minutes old, and your user will be none the wiser!

Here's a demonstration of one way to do this - setting up a front end Apache httpd to divert requests it would normally pass on to a proxy to a local PHP script if the proxy is not available. Simply add something like
  ErrorDocument 503 "/proxydown.php"
into the httpd.conf file, a file it includes, or an appropriate .htaccess file.

Then within that PHP script, you can force a 200 (OK) header to be returned:
  header("HTTP/1.1 200 OK");
and the PHP script can work out what's running, and what was asked for:
  $requested = $_SERVER["REQUEST_URI"];
  $gotinstead = $_SERVER["PHP_SELF"];
may give when you print out those variables
  You called for /dryfeet but it is not available
  You got instead /proxydown.php

This example is a demonstration which I've written to show the sort of thing that can be done when perhaps you have httpd fronting a number of Tomcat servers, and you want the httpd to catch and control any times that it fails to contact a Tomcat. The complete demonstration is [here] - that's a basic framework into which you can add logging, caching, emailin the system adminsitrator if the problem persists, and lots of other facilities.
(written 2013-02-08)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
H307 - PHP - Web2 and caching
  [1633] Changing a screen saver from a web page (PHP, Perl, OSX) - (2008-05-06)
  [1647] Exchange Rates - PHP with your prices in your users currency - (2008-05-19)
  [1733] memcached - overview, installation, example of use in PHP - (2008-08-02)
  [1812] Starting Ajax - easy example of browser calling up server data - (2008-09-27)
  [1813] Ajax - going Asyncronous and what it means - (2008-09-28)
  [1814] Javascript/HTML example, dynamic server monitor - (2008-09-28)
  [1926] Flash (client) to PHP (server) - example - (2008-12-06)
  [1995] Automated server heartbeat and health check - (2009-01-16)
  [2196] New Example - cacheing results in PHP for faster loading - (2009-05-24)
  [2321] Uploading and Downloading files - changing names (Perl and PHP) - (2009-08-04)
  [2545] Scraping content for your own page via PHP - (2009-12-21)
  [3029] PHP data sources - other web servers, large data flows, and the client (browser) - (2010-11-04)
  [3094] Setting your user_agent in PHP - telling back servers who you are - (2010-12-18)
  [3186] How to add a customised twitter feed to your site - (2011-02-27)
  [3458] On this day ... one PHP script with three uses - (2011-09-26)
  [3955] Building up from a small PHP setup to an enterprise one - (2012-12-16)
  [4055] Using web services to access you data - JSON and RESTful services - (2013-03-29)
  [4075] Further recent PHP examples - (2013-04-28)
  [4106] Web server efficiency - saving repetition through caches - (2013-05-30)
  [4136] How do I post automatically from a PHP script to my Twitter account? - (2013-07-10)
  [4627] Caching results in an object for efficiency - avoiding re-calculation - (2016-01-20)

A657 - Web Application Deployment - Using httpd to front Tomcat
  [576] Why run two different web servers - (2006-01-25)
  [631] Apache httpd to Tomcat - jk v proxy - (2006-03-03)
  [1377] Load Balancing with Apache mod_jk (httpd/Tomcat) - (2007-10-02)
  [1566] Strange behaviour of web directory requests without a trailing slash - (2008-03-06)
  [1939] mod_proxy_ajp and mod_proxy_balancer examples - (2008-12-13)
  [1940] URL rewriting with front and back servers - (2008-12-14)
  [1944] Forwarding session and cookie requests from httpd to Tomcat - (2008-12-14)
  [2483] Clustering on Tomcat - (2009-10-30)
  [3018] Tuning Apache httpd and Tomcat to work well together - (2010-10-27)

A655 - Web Application Deployment - Using Tomcat and Apache httpd Together
  [436] Linking Apache httpd to Apache Tomcat - (2005-09-05)
  [1376] Choosing between mod_proxy and mod_rewrite - (2007-10-02)
  [1383] Monitoring mod_jk and how it is load balancing - (2007-10-07)
  [1549] http, https and ajp - comparison and choice - (2008-02-22)
  [1552] Extra public classes in deploying Apache httpd and Tomcat - (2008-02-24)
  [1771] More HowTo diagrams - MySQL, Tomcat and Java - (2008-08-24)
  [1938] Predictive Load Balancing - PHP and / or Java - (2008-12-13)
  [2482] Load balancing with sticky sessions (httpd / Tomcat) - (2009-10-29)


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Some other Articles
Web and console - same principle, same code - Ruby example
Images of Melksham you havent seen before
Helping search engines with appropriate 400 error codes
9 years, and 4000 articles on
Handling failures / absences of your backend server nicely
Travelogue - from the Netherlands to London via Hook and Harwich
Servlet v JSP (Java Server Page). What is the difference?
Tips on Tomcat - moving applications around
Onward from Brussels
On board Eurostar - a running commentary
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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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