[imp] High Availability / Load Balancing

[robert sand]

I am already doing it with 3 servers.  The problem does come in with the sql 
server as being the single point of failure unless you are able to continuously 
sync the horde database over all servers in the pool of imp servers.  We use a 
single server not in the imp pool for the sql database.

Lee wrote:

> The more i think about it, the more worried I get about the SQL sessions 
> implementation. Not only does it require an additional dependancy for 
> horde (we use ldap for prefs), but it more importantly introduces a 
> single point of failure. Ive been giving this some thought and I think I 
> have a far more elegant solutions. I'm not an expert on horde's APIs, 
> but the following seems like it should work:
> 
> Get around the sessions problem:
> 
> We use DNS round robins to distribute load equally based on DNS 
> sequentially resolving each of the servers in the round-robin. Although 
> this continuous round-robin is nice, we could approximate the same 
> distribution by choosing a server only once (when you first load 
> http://webmail.myorg.com). When a user then hits the target horde 
> implementation, horde would rely on the actual server name: 
> http://webmail1.myorg.com, http://webmail2.myorg.com, or 
> http://webmail3.myorg.com.
> 
> 
> Get around the attachments problem:
> 
> Theoretically, when a user adds an attachment (uploads it), horde could 
> create an array called attachments[1] = "path/to/file/uploaded" (like 
> wise for a 2nd, 3rd etc... attachments). When the use then clicks the 
> send button, the send funtion(s) try to attach the files that are store 
> on the server. If the files are not there, horde just uses its 
> attachments array to re-upload the files and attach them.
> 
> 
> I'm really not an expert on horde's APIs, but the above seems like it 
> should both be easy to implement and provide for 100% load balancing 
> capability. If you guys agree, I might start taking a stab at 
> implementing it this week.
> 
> Sincerely,
> Lee
> 
> 
> On Sunday, December 15, 2002, at 11:01 AM, Chuck Hagenbuch wrote:
> 
>> Quoting Dominic Ijichi <dom@ijichi.org>:
>>
>>> auto_prepend_file = "/opt/data/htdocs/sessionlib/adodb-session.php"
>>
>>
>> FYI, you'll probably get better performance using Horde's SQL session
>> handler implementation; as it is, you're loading *two* database 
>> abstraction
>> libraries all the time...
>>
>> -chuck
>>
>> -- 
>> Charles Hagenbuch, <chuck@horde.org>
>> "People ask me all the time what it will be like living without otters."
>>  - Google, thanks to Harpers
>>
>> -- 
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> 
> 
> 


-- 
Robert Sand.
mailto:rsand@d.umn.edu
University of Minnesota, Duluth
Information Technology Systems and Services
144 MWAH
218-726-6122        fax 218-726-7674

"Walk behind me I may not lead, Walk in front of me I may not follow,
  Walk beside me and we walk together"  UTE Tribal proverb.