[CentOS] HA with CentOS

Mon May 14 17:08:59 UTC 2007
Scott McClanahan <scott.mcclanahan at trnswrks.com>

On Mon, 2007-05-14 at 10:55 -0400, Ruslan Sivak wrote:
> 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
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DRBD and Heartbeat seem pretty solid together for cheap affective high
availability.  We've been using them for our production FTP servers
which handle hundreds of thousands transactions a day both
uploading/downloading.  We fail over between the two every 6 months and
haven't had any problems on CentOS 4.3, they've actually been up for
several hundred days now.  There is actually a yumgroup named
drbd-heartbeat in the CentOS extras repository but I don't see that it
is available in CentOS 5.0.  Does anyone know if these packages will be
available in any of the CentOS 5.0 yum repositories?