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mod_proxy_ajp and mod_proxy_balancer examples

One of the major enhancements in release 2.2 of Apache httpd is the addition of the mod_proxy_ajp and mod_proxy_balancer modules to the standard distribution. Gone are the days of needing to build special modules such as Jserv, jk, jk2 and warp to have httpd act as a "front" to a Java (Tomcat) server - the module you need is already there.

Proxy forwarding to a Java Server

Here's an example of a proxied request from Apache httpd on to a server (probably Apache Tomcat) that's running the ajp protocol on port 5090:

ProxyPass /harry ajp://192.168.200.215:5090/latmjdemo
ProxyPassReverse /harry ajp://192.168.200.215:5090/latmjdemo


That's code to be added to the end of your httpd.conf file!

Proxy forwarding to a group of Java Servers

It gets even better ... mod_proxy_balancer lets you define a group of Java servers which you can forward your traffic on to - ideal on a busy site where the background task that's running in Java is a resource hog and needs to be shared between systems. Here's an example of what you would add to httpd.conf:

<Proxy balancer://catbox>
BalancerMember ajp://192.168.200.215:5090/latmjdemo
BalancerMember ajp://192.168.200.214:5009/latmjdemo
</Proxy>
ProxyPass /prince balancer://catbox/


In this example, any references to the web resources on the server under the /prince directory will be forwarded to one of two other machines, on port 5090, and will be directed to the "latmjdemo" web application on there.

On our private Apache Tomcat course yesterday (based on / extended from our public course), we set up exactly this; although a production system would have identical applications on the two servers, we altered the background colour on one of them and it was fascinating to watch different delegates, and different reloads, coming up in either green or white.

More flexibility in forwarding to a group of Servers

The example above uses the default "round robin" scheduler - but there are other facilities available too to help you tune your forwarding. Here's a further example:

<Proxy balancer://kennel>
BalancerMember ajp://192.168.200.219:5009/latmjdemo loadfactor=1
BalancerMember ajp://192.168.200.218:5009/latmjdemo loadfactor=3
BalancerMember ajp://192.168.200.215:5009/latmjdemo status=+h
ProxySet lbmethod=bytraffic
ProxySet stickysession=JSESSIONID
</Proxy>
ProxyPass /corgi balancer://kennel/


In this example, we are forwarding to 2 systems, in a ratio of 1 : 3 and we're allocating traffic based on the traffic quantities coming back from each server rather than the number of requests (so queries that generate a lot of traffic count for more). An extra machine has been designated as "hot swap" if neither of the others is available. Once a visitor is allocated to a particular machine for his forward, he'll continue to be forwarded to that same system while his JSESSIONID cookie remains live.

Some other notes about mod_proxy and family in Apache 2.2:

• ProxyPassMatch is available, which lets you specify a pattern (Regular Expression) for your forwarding - for example, if you wanted to forward all you image requests to an image server:
ProxyPassMatch ^/(.*\.jpg)$ http://images.wellho.net/$1

• mod_rewrite IS aware of mod_proxy_balancer, so that you can rewrite your requests as we do in many parts of our site, and then forward them on to other systems through an appropriate balancer.

• As from Apache 2.2.9, ProxyPassReverse is also mod_proxy_balancer aware.

Further reading ... There's a very good paper by Jim Jagielski - here - on these and more extra facilities. Documentation for mod_proxy_balancer is here, and there's a good description of reverse proxies here.
(written 2008-12-13, updated 2009-05-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
A603 - Web Application Deployment - Further httpd Configuration
  [4001] Helping search engines with appropriate 400 error codes - (2013-02-11)
  [3955] Building up from a small PHP setup to an enterprise one - (2012-12-16)
  [3862] Forwarding a whole domain, except for a few directories - Apache http server - (2012-09-17)
  [3635] Parse error: parse error, unexpected T_STRING on brand new web site - why? - (2012-03-03)
  [3449] Apache Internal Dummy Connection - what is it and what should I do with it? - (2011-09-19)
  [3133] An image from a website that occasionally comes out as hyroglyphics - (2011-01-14)
  [2900] Redirecting a page - silent, temporary or permanent? - (2010-08-03)
  [2478] How did I do THAT? - (2009-10-26)
  [2272] Monitoring and loading tools for testing Apache Tomcat - (2009-07-07)
  [2060] Database connection Pooling, SSL, and command line deployment - httpd and Tomcat - (2009-03-01)
  [1974] Moving a directory on your web site - (2009-01-03)
  [1955] How to avoid duplicating web page maintainance - (2008-12-20)
  [1954] mod_rewrite for newcomers - (2008-12-20)
  [1778] Pointing all the web pages in a directory at a database - (2008-08-30)
  [1767] mod_proxy and mod_proxy_ajp - httpd - (2008-08-22)
  [1762] WEB-INF (Tomcat) and .htaccess (httpd) - (2008-08-20)
  [1707] Configuring Apache httpd - (2008-07-12)
  [1636] What to do if the Home Page is missing - (2008-05-08)
  [1619] User and Group settings for Apache httpd web server - (2008-04-22)
  [1566] Strange behaviour of web directory requests without a trailing slash - (2008-03-06)
  [1564] Default file (MiMe types) for Apache httpd and Apache Tomcat - (2008-03-04)
  [1554] Online hotel reservations - Melksham, Wiltshire (near Bath) - (2008-02-24)
  [1551] Which modules are loaded in my Apache httpd - (2008-02-23)
  [1381] Using a MySQL database to control mod_rewrite via PHP - (2007-10-06)
  [1377] Load Balancing with Apache mod_jk (httpd/Tomcat) - (2007-10-02)
  [1355] .php or .html extension? Morally Static Pages - (2007-09-17)
  [1351] Compressing web pages sent out from server. Is it worth it? - (2007-09-14)
  [1207] Simple but effective use of mod_rewrite (Apache httpd) - (2007-05-27)
  [1121] Sharing the load with Apache httpd and perhaps Tomcat - (2007-03-29)
  [1080] httpd.conf or .htaccess? - (2007-02-14)
  [1009] Passing GET parameters through Apache mod_rewrite - (2006-12-27)
  [934] Clustering, load balancing, mod_rewrite and mod_proxy - (2006-11-21)
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  [755] Using different URLs to navigate around a single script - (2006-06-11)
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  [649] Denial of Service ''attack'' - (2006-03-17)
  [631] Apache httpd to Tomcat - jk v proxy - (2006-03-03)
  [550] 2006 - Making business a pleasure - (2006-01-01)
  [526] Apache httpd - serving web documents from different directories - (2005-12-12)
  [466] Separating 'per instance' data from binaries and web sites - (2005-10-16)
  [345] Spotting a denial of service attack - (2005-06-12)

A608 - Web Application Deployment - Apache httpd mod_proxy
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  [3680] How can I run multiple web servers behind a single IP address? - (2012-04-02)
  [3339] Simplest ever proxy configuration? - (2011-06-28)
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  [2482] Load balancing with sticky sessions (httpd / Tomcat) - (2009-10-29)
  [2325] Apache, Tomcat, mod_proxy - (2009-08-06)
  [2273] Three recent questions on Tomcat Convertors - (2009-07-07)
  [2062] Virtual hosting and mod_proxy forwarding of different domains (httpd) - (2009-03-01)
  [1944] Forwarding session and cookie requests from httpd to Tomcat - (2008-12-14)
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A657 - Web Application Deployment - Using httpd to front Tomcat
  [3999] Handling failures / absences of your backend server nicely - (2013-02-08)
  [3018] Tuning Apache httpd and Tomcat to work well together - (2010-10-27)
  [2483] Clustering on Tomcat - (2009-10-30)
  [1940] URL rewriting with front and back servers - (2008-12-14)
  [576] Why run two different web servers - (2006-01-25)

A900 - Web Application Deployment - Tomcat - Extra Features
  [1899] Virtual Hosting under Tomcat - an example - (2008-11-22)
  [1896] Virtual Hosts and Virtual Servers - (2008-11-20)
  [1383] Monitoring mod_jk and how it is load balancing - (2007-10-07)
  [1370] Apache Tomcat Performance Tuning - (2007-09-29)


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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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