[CentOS] HA with CentOS

Mon May 14 14:55:50 UTC 2007
Ruslan Sivak <rsivak at istandfor.com>

Steve Huff wrote:
>
> On May 14, 2007, at 10:25 AM, Ruslan Sivak wrote:
>
>> Steve Huff wrote:
>>
>> If you set up a third box to be the shared storage, doesn't that now 
>> become the single point of failure?
>
> Short answer: maybe. :)
>
> Longer answer: If you set up your shared storage according to 
> upstream's guidelines, as described in the documentation 
> (http://mirror.centos.org/centos/4/docs/html/rh-cs-en-4/ch-hardware.html#TB-HARDWARE-NOSPOF), 
> then you provide at least two channels of communication between each 
> component in the cluster.  In addition, you choose a platform for 
> shared storage that provides some redundancy of its own, whether it's 
> multi-controller HW RAID, or multiple storage nodes on a SAN, or what 
> have you.
>
> CS/GFS operates under the assumption that your shared storage is 
> fault-tolerant; its job is to make your services fault-tolerant.  Is 
> the recommended "no single point of failure" configuration proof 
> against your data center burning down, or against a madman with an 
> axe?  Unlikely.  Will it allow you to host services in a way that is 
> considerably more robust and flexible than hosting them on a single 
> box?  Yes.
>
> -Steve
>

I am currently running a redundant environment on windows by having 2 
boxes with apache and having the data (images) be synced over 
automatically between servers using FRS (File Replication Service).   
This works well most of the time, except for when it breaks, at which 
point I need to resync the two servers, which usually takes days. 

I would like to set up something similar using linux.  I don't have the 
budget for a SAN/NAS, and even having a third server as storage would 
probably not be worth it, although we can possibly go with this.  The 
problem, is that it would be a single point of failure. 

Is there some service/filesystem in Linux that allows for the automatic 
replication of files to make a fault tolerant environment possible with 
only 2 servers?  Basically whenever there is an update of a file on a 
certain file system (certain folder), the file gets synced over to 
another system. 

Russ