(Simple?) High availability question

[tleslie]

I have already gone down this road,
and end up with the scary sol'n
of about 1.2 M $  of oracle licensing,
which when bought at that volume,
comes down to about 600-700K$.

IBM DB2 looks good, but its only about 30-40% cheaper.

This whole cpu/cpu-core/socket licensing is also a nightmare.

i think pgcluster (or is it pgpool) 2.0 is out now, 
and for a small task on a simple system set up with a 
good chance to test and burn in, might give you what you want.

I expect will see good stuff in 12-18 months.

If you use java DB connectors there is also a few propri 
projects out there that are reasonably priced.

For me , I have gone with a Oracle RAC and 
mutli site redundancy with a Netapp dual head
8GB fibre redundant SAN behind the scenes,
which gives a pretty good sol'n,
well ..... i'll say for sure once I have
built it! for north of a M$ it hopefully will.

-tl

On Fri, 2007-06-01 at 17:15 -0400, Madison Kelly wrote:
> Lennart Sorensen wrote:
> > Well running primary/secondary bind is trivial.
> 
>    Aye, this was the least of my concerns. :P
> 
> > Running identical web servers is not too hard, although you have to
> > update both whenever you make page changes.  Doing round robin
> > connection distribution with a load balancer at the firewall isn't too
> > hard, and there are probably better load balancers that take system load
> > of each web server into account as well as checking that the web server
> > is working and such.
> 
>    Since posting I found this: 
> http://www.howtoforge.com/load_balancing_apache_mod_proxy_balancer
> 
>    I'll be running 2.2, so this should help deal with the apache side of 
> things pretty easily.
> 
> > Running two mail servers is harder.  When a user reads or deletes a
> > message, how do you ensure the update occours on both?  Redundant mail
> > reception isn't too hard since you just have one be the main mail server
> > and the other a backup MX which simply holds and forwards mail to the
> > primary when it comes back up (most of the time the primary receives the
> > mail directly).
> 
>    The mail reception I wasn't worried about exactly because of the 
> simplicity of using multiple MX records. As you pointed out, it's the 
> directing users to their mailbox and keeping both in sync where the 
> trouble starts. This might be a better candidate for a share FS?
> 
> > Redundant pgsql is VERY hard.  If all you want is static database data
> > then it wouldn't be a big deal and you could treat it like the web
> > server.  Of course this is almost never what anyone wants.  Last I
> > checked postgresql did not have live replication support, which is
> > basicly what is needed.  This is one of those places where oracle and
> > db2 have a reason for existing.  I believe mysql has a replicating
> > server backend, although apparently that backend is much slower and has
> > less features than the regular one, so it is a major tradeoff there.
> > People are working on replication support for postgresql, but they have
> > been working on it for years and I don't think it is working yet.  It is
> > a very complicated thing to implement.  Keeping in sync when two servers
> > are both up and already in sync is no big deal.  Getting back in sync if
> > one has been down is very hard, especially while data is still changing
> > on the live server.
> 
> Foo. I was under the impression that is exactly what clustering was 
> about. Is there a way to used a distributed file system (like coda) and 
> have two servers talking to the save directory structure? I am going to 
> go out on a limb and guess no.
> 
> I may have to give up the idea of having load balancing at this time and 
> stick with having the second server keep a mirror of the main server 
> with a heartbeat between the two to have the backup take over on a 
> failure of the main. Seems like a sad waste though with the second 
> server just sitting there. :(
> 
> The main websites I care most about uptime on use PgSQL and have 
> frequent writes. Have you (or anyone) played with how to handle 
> mirroring the WAL of PostgreSQL? I can run a simple 'rsync' on the 
> backup server say every 5m but that won't help if the master failed 
> after an rsync (very likely) and without an up-to-date copy of the WAL 
> rebuilding the missing bits would be, if I understand it all right, not 
> possible. I could have a script run on the master that dumps the 
> databases very frequently and have the most recent loaded on failure but 
> I'd still lose any changes between the last dump and the failure.
> 
> I hope I can come up with something more robust. Perhaps I'll have to 
> look into slony more.
> 
> Thanks!!
> 
> Madi
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