On 3/8/07, Christopher Schultz <[EMAIL PROTECTED]> wrote:
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Leon,
Leon Rosenberg wrote:
> On 3/7/07, Christopher Schultz <[EMAIL PROTECTED]> wrote:
>> Load balancing pretty much always comes down to either:
>> 1. A single point of failure (Apache httpd, BigIP, or whatever).
>
> Loadbalancers usually come in pairs :-)
Er, you can buy a single load balancer off the shelf. One input port,
many output ports (virtually, that is). It's not uncommon to see a
single device acting as a load balancer.
Load-balanced /resources/, on the other hand, generally come in
multiples (otherwise, what's the point?).
If you had a pair of load balancers, how would you pick which one
handles the request? ... R-R DNS, anyone?
one is active one is standby. Same applies to the firewall and the switches.
>> It seems to me that the most robust deployment for a webapp is:
>>
>> Random request distribution + Apache httpd + lb'd Tomcat
>
> paired firewalls + paired loadbalancers + tomcat cluster.
> Performs much better as the above :-) Try it out, give it a chance.
But the request has to come from somewhere and go to a single device. If
you have pairs of things, you have to divide the traffic, which brings
me back to R-R DNS. Otherwise, you have a set of hardware that never
gets used.
andrew already explained how this works with a pair of lbs.
I'm not sure how your "better" layout is any different than mine, except
that you've replaced Apache-httpd-based-load-balancing with what looks
like appliance-based-load-balancing and put firewalls out front (which
is logically insignificant).
much more availability? Ideally, in a stateless or session-lbed
application the user will never be affected if a machine dies :-)
And yes the firewalls are insignificant. But nowerdays, with all that
bot-nets and stuff, you really want them to handle the dos :-)
- -chris
regards
Leon
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