inline commentary yet again...
>>All the main data is in a centralized database.
...
>>Just make sure the Database machine is rock solid.
> This is where I was thinking about the multi-master database. I can't
> use just one database because that still gives me a single point of
> failure which is a bad thing. It shouldn't be too hard since MySQL
> supports this now.
The database can either be a pair of machines, or you just get one big
fat beefy badass box as your webserver. I worked for an online shop in
the states that had doubled hardware that ran in lockstep, but those are
silly expensive. I think NEC makes them,
>>The only thing you need to really worry about is both websesrvers
>>replicating work with their cron jobs
> Unfortunately, it would be very difficult to prevent race conditions
> here, especially if the clocks on the servers had significant drift.
> With a heartbeat, it would allow a more serialized process which would
> prevent race conditions. Of course, where do I put my heartbeat
> server ;-). Can two heartbeat servers monitor the same boxes? How
> does that work?
You don't use a heartbeat server at all. Each webserver has a script
that loops every N seconds that checks in with a table on the database
that updates its own record
Then it checks the records of the other machines against it. The records
use the DATABASE clock for timestamping (with a "NOW" function or
whatever) to the time is always relative to the database clock.
If it tries to check the database and THAT is down, wewll, you have
bigger peoblems on your hands and the webserver can raise all sorts of
alarms, send pages, and make a general huge fuss.
2012 Olympics are in London, by the way.
--
-Tony Saurini
Eitri Ltd.
[EMAIL PROTECTED]
eitri. we make hammers.
Big Hammers.
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