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Private, public, and hybrid clouds are different ways of deploying infrastructure and applications in a cloud computing model. A public cloud is an environment made available over the internet, that anyone can subscribe to and then access. A private cloud, as the name implies, is the infrastructure used by just one organization. A hybrid cloud is a combination of the two other types.
All three provide a common set of advantages over traditional on-premises IT environments: affordability, reliability, scalability on demand, and consistently high performance. The implementation choice depends on a number of factors including the kind of workload, security needs, budgetary considerations, and the extent of your in-house IT expertise. The three cloud types are not exclusive to one another. In fact, an increasing number of companies now deploy all three.
Public clouds are the most pervasive and well-known cloud computing model. All the resources needed to run the infrastructure – servers, storage, networking components, and supporting software – are owned and managed by the third-party provider, and accessed by your users over the Internet via a web browser. Examples of public clouds are Amazon Web Services, Microsoft Azure, and Google Cloud Platform.
Public clouds are multi-tenant: you share the infrastructure with other organizations, but your data and workloads are kept isolated from theirs in a safe and secure virtual space. Rather than having to own and operate the hardware, you rent it by subscription, paying only for the services you actually use.
Public clouds offer a number of advantages:
Lower costs
A public cloud effectively shifts your IT spend from a capital expenses (CAPEX) framework to an operating expenses (OPEX) model: instead of making a large upfront investment to purchase and install hardware and software, you just pay for what you use. The overall required IT budget – known as the total cost of ownership (TCO) -- is generally much lower than for traditional on-premises infrastructure.
On-demand scalability
Providers possess immense resources that you can scale up whenever needed to meet periods of peak demand and then scale down again afterward.
Reduced complexity
With traditional on-premises systems, as much as 80% of IT time and resources are consumed by merely “keeping the lights on.” The public cloud eliminates most of this expense and complexity. This lets you maintain a much smaller cadre of IT experts in-house, focused on building and delivering high-value products and services.
Flexible pricing options
Cloud providers offer different tiers of service, known as service level agreements (SLAs). Higher guaranteed levels of speed, availability, and resource provisioning come at a premium; you can choose these for mission-critical workloads and pay a lower rate for less vital and lower-use applications. You can also shop around for the best combination of price and performance in today’s highly competitive public cloud marketplace.
There are some limitations to public clouds:
A poor fit for sensitive and confidential workloads
Some industries, such as finance and healthcare, require very high levels of security and are subject to strict privacy controls. These factors make public clouds inappropriate or preclude them outright.
High expense
The public cloud can impose a pricey TCO for high-use enterprise-wide deployments within midsize to large organizations.
Limited infrastructure visibility and control
The cloud provider runs, maintains, and secures the infrastructure according to standards and strategies they set and enforce. These may not be sufficient to meet regulatory requirements for your particular industry.
A private cloud is a computing infrastructure devoted to use by a single organization. It can be housed at your own data center facility or at that of a third-party service provider. The defining characteristic is that the IT resources are run and maintained on a private network for your use alone.
Unlike public clouds, a private cloud is not shared with anyone else. This makes customization and regulatory compliance easier to manage, which is why private clouds are often utilized by financial institutions, government agencies, and heavily regulated industries that need to exercise a high degree of control over their workloads.
Private cloud advantages include:
Stringent security
An environment dedicated to a single customer affords maximum levels of protection against unauthorized data access and theft.
Regulatory compliance
Private cloud infrastructure can be tailored to conform to strict, mandatory privacy and governance rules for sensitive and confidential workloads and data.
High performance
You can easily equip a private cloud to meet your specific standards for availability and throughput.
Flexibility to respond to changing needs
Because the environment is for your use alone, you can transform it to respond to evolving technology, markets, and opportunities.
Private clouds do impose some drawbacks:
Limited mobile access
Stringent security measures can make it difficult to enable private cloud access for users of mobile devices.
High CAPEX and overhead
Major upfront capital investment, lengthy deployment cycles, and extensive in-house IT expertise are all necessities for a private cloud owned and operated by the organization itself.
Scalability limitations
Scaling up can be resource- and time-intensive owing to the necessity to purchase and configure both hardware and enabling software.
Hybrid clouds combine public and private cloud resources to yield the advantages of both. High levels of integration and orchestration are must-haves to enable seamless movement of data and applications between the two types as needs change. Confidential operations like financial reporting, for example, can be run on a private cloud. High-volume, less sensitive workloads like web-based email – or even temporary workloads such as development and test – can run on a public cloud. In addition, public cloud resources can be harnessed to meet short-term demand spikes for private-cloud applications (a technique known as “cloud bursting”). This avoids the high CAPEX of having to purchase and provision extra capacity to be used only intermittently.
The primary motivation is twofold: acquiring the flexibility to choose the optimal cloud for each application, and gaining the ability to move workloads freely among clouds as dictated by changing circumstances. A hybrid cloud strategy enables the organization to meet its technical and business objectives more cost-efficiently and effectively than it could with either a public or private cloud alone.
Running a hybrid cloud offers a number of benefits:
Compliance and security
Confidential applications can be operated privately while less sensitive workloads can be deployed to a public cloud.
High flexibility
You can respond immediately and effectively to unpredictable demand surges with public cloud infrastructure, and scale back down when the spike subsides, with no impact on other workloads running in your private cloud.
Resource optimization
Flexibly deploy applications to maximize utilization of both on-premises resources and cost-saving public cloud infrastructure.
Ease and agility
Alter your blend of public and private deployments in response to changing needs and opportunities. A hybrid cloud also lets you modernize legacy applications on a gradual basis, rebuilding and migrating them to cost-efficient public cloud infrastructure comfortably over time.
High reliability
Applications and data can be distributed across multiple data centers for highly effective redundancy, failover, and disaster recovery.
Even with its “best of both worlds” status, the hybrid cloud model does present some challenges:
Elevated cost
Running, maintaining, and optimizing the on-premises segment of a hybrid cloud is an expensive proposition, especially for smaller organizations.
Infrastructure complexity
For a hybrid cloud to deliver maximum benefit, its public and private components must be strongly linked and orchestrated. Management, integration, and security become increasingly complex as the number of clouds proliferates, especially when sourced from different providers.
A hybrid cloud refers to a combination of the two cloud types, private and public – in its simplest form, an environment containing one of each.
Until recently, multicloud was the term used for architectures composed exclusively of public clouds: at least two but more often a greater number, and furnished by more than one cloud services vendor.
The last several years have seen significant advances in the strategy known as hybrid multicloud: “hybrid” referring to the presence of a private cloud in the mix, and “multicloud” indicating more than one public cloud from more than one service provider. As enterprises increasingly move in this direction, the hybrid multicloud (or nowadays, also known simply as hybrid cloud) looks to become the predominant IT environment, at least for larger organizations.
While smaller businesses in unregulated industries tend toward the cost advantages of public cloud, larger organizations frequently run more than one type. Each kind of cloud has its appropriate time and place. It all depends on your resources and use cases.
The public cloud is most suitable for situations like these:
Predictable computing needs, such as communications services for a mostly fixed number of users
Applications and services critical for IT and business operations
Reserve resources provisioned to meet peak usage situations on demand
Software development and test environments
A private cloud is often used by:
Highly-regulated industries and government agencies
Technology companies that require strong control and security over their IT workloads and underlying infrastructure
Organizations with the resources and requirements to invest in advanced technologies delivering the highest performance and availability
A hybrid cloud model is most appropriate for:
Enterprises serving multiple vertical markets with different IT security, regulatory, and performance requirements
Optimizing the overall cloud investment while leveraging the advantages of both public and private cloud models
Providing enhanced security for solutions such as SaaS workloads that need to be delivered via secure private networks
An agile cloud strategy dictating frequent alternation among providers and clouds to obtain the best combination of price and performance for various workloads