Pavnay

When 2 application servers run together, it's not simple to have a right management for response codes and the famous 404 page.

Where manage this page ? In httpd ? In tomcat ? How to be sure that it's correctly configured ?

Sometimes, we have several application servers on different computers and we want that applications hosted on them can be accessed from a unique entry point.
This entry point is often behind a domain name mapped on a unique IP address. It's possible to provide several application serves with one httpd Apache server which will be the entry point.

This one can authorize access to applications with htaccess.

The bandwith increase allows now a better comfort for users but also an explosion of multimedia resources. There many kinds of resources :

• images : images are always bigger;
• the "web 2.0" involves lots of CSS and Javascript scripts;
• HTML pages

For static resources as images, it's possible to take advantage of browser cache, likewise for CSS and Javascripts.
However, these last resources tend to be bigger and longer and so disturb page construction because of data transfert delays.
It's possible to speed up these delays with httpd thanks to the deflate mode.

Because web sites are more and more aesthetics and as a result need more and more static resources (javascript, CSS or images), it's mandatory to use a cache policy. There are many sophisticated tools as cache servers (Squid), CDN but there is a simple and often forgotten method : the browser cache.
The browser cache usage is simple to do and consists in setting headers in the HTTP response. Setting up these headers is quiet simple with the httpd server provided by the Apache Foundation.

MySQL allows to set up database replication to have bases redundance.
There are many advantages to have replication :

• to carry out server redundance : if a database server crashs, the server in replication can take its place,
• to set up a loadbalancing on requests, for example with ipvsadm.

Replication is not magic, albeit it is easy to do, it brings constraints and complications if there is an important delay. Of course, it's needed to don't write data on a slave to preserve database integrity...
In this article, we will see how to set up replication and how to manage it...