On Jan 19, 2009, at 12:27 PM, Larry Ludwig wrote:
>> What the CPU is doing isn't really relevant, the EC2 machines are
>> really just Xen instances, and you pay for every hour (or portion of
>> an hour) that the instance is booted, regardless of whether it is
>> working or not.
>
> So it's not based upon CPU/hour, really instance/hour? Forgive me on
> this issue as I haven't researched that much into this part of their
> pricing.
>
> So $72 for the full month (small) if an instance is kept running the
> full time. Seems similar pricing for what would the CPU part of a
> dedicated server would cost.
>
And if you only have a handful of servers and keep them running all
the time, then it doesn't really buy you much to put it in EC2, but if
you need a lot of servers on an infrequent basis, this can save some
big bucks.
>> when ( load is greater X for Y minutes ) {
>> total=count_total_number_of_running_instances()
>> recent=count_number_of_instances_started_in_the_last_hour()
>> if ( total < MAX_TOTAL AND recent < MAX_RECENT ) {
>> start_a_new_instance()
>> } else {
>> notify_administrator()
>> }
>>
>
> This might be a fine script for simple auto-scaling, but using load as
> a metric IMHO is a terrible method to determine scaling. Reasons:
Well, in this pseudo-code, I really meant load as 'an indication that
your application is requiring more resources that the current
instances can handle' rather than simply the system load average. In
my particular case most of my instances are processing requests from a
queue, and my definition of load encompasses primarily the length of
the queue backlog and the estimated time to process the backlog with
the currently available instances.
--
Jason Kohles, RHCA RHCDS RHCE
em...@jasonkohles.com - http://www.jasonkohles.com/
"A witty saying proves nothing." -- Voltaire
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