Which Types of Workloads to Run in Public, Private Clouds

Should you use a private or public cloud? Here are pros and cons for each mode when it comes to certain workloads.

Cloud consumers and administrators love being able to serve themselves. And for public cloud service providers, self-service isn’t an afterthought; they have deliberately made it the only way to control your resources, see your bill and use your services. For this reason, public cloud self-service quality is incredibly high, with quality user interfaces and APIs.

Private cloud software has improved to now offer users self-service and, at least from the point of the users ordering extra virtual machines, things are better than they used to be. However, if you want more than virtual machines, you might find that private clouds have fewer offerings via their self-service front ends, and these self-service capabilities are often clunky and poorly integrated—leading to a poor user experience. Additionally, APIs can be complex or completely missing.

Public cloud providers make enormous investments and innovations in their networking. They might provide their own content delivery networks, points of presence and new ways of software-defined networking. They also often have a global presence that means your cloud resources can be available worldwide. However, because these public cloud providers are so large and innovative, their networks have a history of issues with load balancers, “noisy neighbors” and, as one industry commentator cheekily put it, their own “weather patterns.”

Private clouds running inside an enterprise benefit users because they are on the corporate network and should thus be available to all. Most organizations have fast local and wide- area networks connecting users to the data center, within which the private cloud resides. The downside is that enterprise networks can be under-funded, which leads to fragmented and poorly performing networks that directly impact both user experience and the ability to connect to cloud services.

The average public cloud provider offers a multitenant cloud, pooling resources that it then divides up for individual cloud customers. Storage is architected in pools that are then replicated many times across many locations and also shared among many tenants. This is a mature operation, but there can still be differences in the service you get, often because the network is one of the most shared (and complex) resources.

In a private cloud, the same architectural pooling is possible on a smaller scale, and similar mechanisms exist to create and share multitenant resource pools using software such as OpenStack. However a private cloud is single tenant, so the resource pooling has a lower isolation requirement because the whole cloud is isolated.

This is the biggest difference between public and private clouds because it’s about size and responsiveness. Elasticity of resources, up or down, with the requisite changes in billing, is the raison d’etre of cloud. It’s what allows people to save money and yet still be agile and experimental.

Private clouds offer consumers elastic resources, but they are ultimately constrained by the enterprise IT procurement process. Users can consume all they want up to the ceiling, but to move the ceiling up takes time—and financial justification.

Public cloud systems offer limited, but increasingly better, operational systems for cloud customers. They are constantly optimizing the provider end of resources to balance acceptable performance with density. These cloud operational systems are built for cloud so they integrate and operate very well, but they may lack the detail that the enterprise user expects.

In an elastic, self-service system, the cloud platform needs some “smarts” to optimize itself and to help the administrator make sense of a constantly moving system. Visual operations systems then integrate with such a resource scheduler to allow both dynamic and human modification of cloud resources. However, the downside is that enterprise-grade optimization tools often aren’t built specifically for cloud, but they are slowly being integrated and modified over time.

Public cloud is more advanced than any private cloud, and it’s becoming easier to use and more integrated with the enterprise. The rate of feature releases and reducing price levels at the leading cloud service providers also make a compelling case for public cloud. Private cloud may be comforting to enterprise IT staff, but the cons are stacked with constraints and costs.