High Availability

[shimi]

2010/4/15 Boaz Yahav(berber) <berber at weber-sites.com>

>  I guess this is more a theological question.
>
>
>
> Would you build a web site  infrastructure that needs to be highly
> available using a single machine where the front end servers are virtual
> servers?
>
> Is this even considered highly available or might it be what's some may
>  call "partially highly available J"?
>
>
>
Using Linux more than a decade, I can say that if you're competent enough as
a system administrator (which you should be, if you "go big" and start
high-availability-ing your stuff - you need to understand what you're doing)
- I've learned that most of the time, a downtime of a Linux system is due
to... hardware issues;

So, if you trust your hardware platform (single machine), there is really no
point in partitioning your hardware power to multiple "machines" that all do
the same thing - you just add more overhead, and more stuff to manage, and
when your hardware fails, you're not going to be highly available, but
instead, not available at all ;)

So no, I think the key for high availability is:

* Redundancy - the more the merrier - and nothing should depend on nothing
else - meaning - there should be no single point of failure [ = one thing
that breaks that makes everything go down. A good example is Shared
Storage.... ]
* Quality Hardware (I personally prefer HP - continuing the line of Compaq
from the past)
* Reliable OS! Can't stress this enough. Of course, reading this on linux-il
- you've already made the right choice ;)

Also remember that your hardware and software are not alone in the game. A
website needs to be connected to the Internet. Even if you hardware and
software are up 24/7/365 - if your switch/router/network connection dies for
some reason, the web site will still be down, as far as the customers care.
So you need multiple network connections from multiple ISPs on your own IP
netblock that you can advertise to all the links that are currently up :-)

HTH,

-- Shimi
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