Friday, April 09, 2010

Common Cloud Myths

Over the last three years, I've spent an increasingly disproportionate amount of my time dealing with cloud myths. I thought I'd catalogue my favourites by bashing one every other day.

Cloud is Green

The use of cloud infrastructure certainly allows for more efficient provision of infrastructure through matching supply to demand. In general :-

1. For a traditional scenario where every application has its own physical infrastructure then each application requires a capacity of compute resources, storage and network which must exceed its maximum load and provide suitable spare capacity for anticipated growth. This situation is often complicated by two factors. First, most applications contains multiple components and some of those often highly under utilise physical resources (for example load balancing). Second, due to the logistics of provisioning physical equipment then the excess capacity must be sufficiently large. At best, the total compute resources required will significantly exceed the sum of all the individual peak application loads and spare capacity.

2. The shared infrastructure scenario covers networks, storage and compute resources (through virtualisation). Resource requirements are balanced across multiple applications with variable loads and the total spare capacity held is significantly reduced. In an optimal case the total capacity can be reduced to a general spare capacity plus the peak of the sum of the application loads. Virtual Data Centres, provisioning resources according to need, are an example of shared infrastructure.

3. In the case of a private cloud (i.e. a private compute utility), the economics are close to that of a shared scenario. However, there is one important distinction in that a compute utility is about commodity infrastructure. For example, virtual data centres provide highly resilient virtual infrastructure which incur significant costs whereas a private cloud focuses on rapid provision of low cost, good enough virtual infrastructure.

At the nodes (the servers providing virtual machines) of a private cloud, redundant power supplies are seen as an unnecessary cost rather than a benefit. This ruthless focus on commodity infrastructure provides a lower price point per virtual machine but that necessitates that resilience is created in the management layer and application (the design for failure concept). The reasoning for this, is the same reasoning behind RAID (redundant array of inexpensive disks). By pushing resilience into the management layer and combining more lower cost, less resilient hardware you can actually enable higher levels of resilience and performance for a given price point.

However, the downside is that you can't just take what has existed on physical servers and plonk it on a cloud and expect it to work like a highly resilient physical server. You can however do this with a virtual data centre.

This distinction and focus on commodity provision is the difference between a virtual data centre and a private cloud. It's a very subtle but massively important distinction because whilst a virtual data centre has the benefit of reducing educational costs of transition in the short term (being like existing physical environments), it's exactly these characteristics that will make it inefficient compared to private clouds in the longer term.

4. In the case of a public cloud infrastructure (a public compute utility), the concepts are taken further by balancing variable demands of one company for compute resources against another. This is one of many potential economies of scale that can lead to lower unit costs. However unit cost is only one consideration here, there are transitional and outsourcing risks that need to be factored in which is why we often use hybrid solutions combining both public and private clouds.

The overall effect of moving through these different stages is that the provision of infrastructure becomes more efficient and hence we have the "cloud is green" assumption.

I pointed out, back in 2008 at IT@Cork, that this assumption ignored co-evolution, componentisation and price elasticity effects.

By increasing efficiency and reducing cost for provision of infrastructure, a large number of activities which might have once not been economically feasible become economically feasible. Furthermore, the self-service nature of cloud not only increases agility by enabling faster provision of infrastructure but accelerates user innovation through provision of standardised components (i.e. the infrastructure equivalent of a brick). This latter effect can encourage the co-evolution of new industries in the same manner that the commoditisation of electronic switching (from the innovation of the Flemming valve to complex products containing thousands of switches) led to digital calculators and computers which in turn drove further commoditisation and demand for electronic switching.

The effect of these forces is that whilst infrastructure provision may become more efficient, the overall demand for infrastructure will outstrip these gains precisely because infrastructure has become a more efficient and standardised component.

We end up using vastly more of a more efficient resource. Lo and behold, cloud turns out not to be green.

The same effect was noted by Willam Stanley Jevons in the 1850s, when he "observed that England's consumption of coal soared after James Watt introduced his coal-fired steam engine, which greatly improved the efficiency of Thomas Newcomen's earlier design"

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