[KLUG Programming] PHP application & fault tolerance

[phillip hebenstreit]

Hello all,

I'm on a fact finding mission before starting development on a web 
application, we are considering using PHP for this, here are some 
requirements listed below.  Could anyone give me any suggestions based on 
their experience with PHP application development?

I am sorry if I miss something or do not describe myself clearly, please 
excuse me if I forget something obvious.  I'm in that great position of 
learning as I go.

requirements
   fault tolerant web application
   sql replicated across 2 servers
   apache fault tolerant
   application needs a high level of up-time
   user should experience very little down time

known information
   sql replication is well documented,  so sql part is taken care of.

unknowns
   apache's fault tolerance ability
   php's fault tolerance ability

background
   this is within the range of a "normal" web application, just needs to be 
fault tolerant in case a server goes down.
    user logs in
    application stores data from user in MySQL tables
    get data using queries
    pages & menu's are user friendly
    pages display info from database using the queries
    reports output using queries
    all the stuff most every website does

question:
   Is there a way to develop this using PHP so that if my primary Apache 
server goes down, my PHP application can continue running with minor or no 
user downtime?


ideas:
   I suspect, if I cluster the apache side that would take care of the 
apache part, but  could the PHP application still function if the specific 
apache server the user is on goes down or would the PHP part fail?

alternatives:
   I am thinking this would need to be done as a Java application, because 
of the fault tolerance requirements, since the Java could be running on the 
user's computer and would have logic that could direct it to a list of 
servers based on availability.  (or could this also be done with PHP? )


thanks very much,

Phillip