On Thu, 2009-12-17 at 20:32 +1100, Peter Rundle wrote:
> G'day Sluggers,
> 
> I've inherited a LAMP stack which uses the php session stuff to maintain a 
> session with an authenticated user. A cookie gets sent 
> to the user and upon it's return PHP retrieves the "session" from a file in 
> the "sessions" folder.

I don't know php, but there is usually some distributed means to make
sessions work, I'm sure someone else will pop up.

> I would like to change the setup such that the site could be hosted on 
> multiple web servers. The PHP sessions would then be badly 
> broken because the user could potentially be directed to the "other" server 
> depending on what load balancing solution was used, 
> which would not have the matching "sessions" file. I do not want to use a 
> solution that has the load balancer direct the user back 
> to the same server because a lot of the reason for load balancing is for 
> redundancy or to be able to take a server off-line to 
> service / upgrade it etc.
> 
> The multiple web servers would initially share a a single back-end DBMS 
> server, but in future would have their own dedicated 
> back-end DBMS, with the DBMS servers using replication to keep in sync.

There are two separate issues: load & redundancy.  I suggest you shard
for load, and single master replicate for redundancy, what you wrote
above suggested multi-master replication, and thats painful.

-Rob

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