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Why Auto-Scaling In the Cloud Is a Bad Idea
George Reese writes "It seems a lot of people are mistaking the very valuable benefit that cloud computing enables — dynamically scaling your infrastructure — with the potentially dangerous ability to scale your infrastructure automatically in real-time based on actual demand. An O'Reilly blog entry discusses why auto-scaling is not as cool a feature as you might think."
i think the author's point is that dynamic scaling should always be planned; partly because it results in better understanding of traffic patterns, and thus better long-term capacity planning, and partly because you need to be able to distinguish between valid traffic and DDoS attacks. still, i think the author is overstating it a bit. one of the main draws of cloud computing to smaller businesses is the ability to pool resources more efficiently through multitenancy, part of which is precisely due to auto-scaling. without the cloud being able to dynamically allocate resources to different applications as needed in real-time (i.e. without human intervention), there isn't much of an advantage to sharing a cloud infrastructure over leasing dedicated servers.
for instance, let's say there are 10 different startups with similar hosting needs, and they can each afford to lease 10 application servers on their own. so using traditional hosting models they would each lease 10 servers and balance the load between the them. but after a few months they realize that 75% of the time they only really need 5 servers, and 20% of the time they need all 10, but an occasional 5% of the time they need more than 10 servers to adequately handle their user traffic. this means that in their current arrangement, they're wasting money on more computing resources than they actually need most of the time, and yet they still have service availability issues during peak loads 5% of the time (that's over 2.5 weeks a year).
all 10 of these startups share a common problem--they each have variable/fluctuating traffic loads severely reducing server utilization & efficiency. luckily, cloud computing allows them to pool their resources together. since the majority of the time each startup needs only 5 servers, the minimum number of virtual servers their cloud infrastructure needs is 50. and since each startup needs double that 20% of the time, 10 extra virtual servers are needed (shared through auto-scaling). but since each startup needs more than 10 servers for about 2.5 weeks each year, we'll add another 15 extra virtual servers. so all in total, the 10 startups are now sharing the equivalent of 75 servers in their cloud.
by hosting their applications together on a cloud network, each startup not only has their hosting needs better met, but they also stand to save a lot of money because of better server utilization. and each startup now has access to up to 30 virtual servers when their application requires it. this kind of efficiency would not be possible without a cloud infrastructure and auto-scaling.