What’s the Difference Between Public Cloud and Private Cloud?

Private cloud and public cloud are two cloud computing models where you access on-demand IT resources over a network, such as data storage, databases, software, or analytics services. In a private cloud, a single organization controls and maintains the underlying infrastructure that delivers the IT resources. In a public cloud model, external cloud providers deliver the resources as managed services.

For example, consider a medium-sized organization with separate finance and marketing departments. Each needs computing resources, but for different applications. In a private cloud solution, the organization purchases server hardware and maintains it in a central data center, either on-premises or off-site. The organization runs virtualization solutions over the top, which the finance and marketing departments can provision by self-service. This setup offers a single operating location and delivers resources to the different departments.

In a public cloud setup, teams access managed, external cloud services. These services might be across different locations, unless specified in the configuration. Each department accesses and controls resources through self-service, which are then delivered over a network.

Read about private clouds »
Read about public clouds »

Amazon first introduced cloud services as Amazon Web Services (AWS), initially providing cloud compute and cloud storage over the network. In the following years, other large organizations attempted to recreate this model on their own internal hardware.

Both the public cloud and private cloud models exhibit the five characteristics of cloud computing defined by NIST:

1. On-demand self-service
2. Broad network access
3. Resource pooling
4. Rapid elasticity
5. Measured services

The term private cloud was introduced to distinguish between internal cloud environments that businesses maintain for themselves and third-party, public cloud services provided by organizations such as AWS.

Cloud infrastructure on demand

Both public and private clouds virtualize and share computing resources such as hardware, software, networking, servers, and storage over a network. Users can allocate and release resources as needed, as well as manage infrastructure configurations, using management consoles or APIs.

For example, users can provision and configure several application servers using the Amazon EC2 console. If Auto Scaling Groups are configured, the servers automatically scale virtual machines up or down based on demand.

Similar underlying cloud technologies

Both types of cloud environments have similar underlying technologies. They use virtualization to abstract underlying hardware and deliver it using interfaces such as APIs. Both models also provide support for automatic scaling, automated orchestration, fault resiliency, and improved backup and recovery systems.

Operational efficiency

Both public and private clouds improve operational efficiency in an organization's IT infrastructure. Organizations reduce costs by centralizing infrastructure management. On-demand service provisioning can help decrease time-to-market for new projects, products, and services. Scalability can help reduce bottlenecks in service delivery.

A public cloud typically brings more operational efficiency across a range of use cases than private cloud services, due to a wider range of services and delivery types.

It’s difficult to replicate public cloud infrastructure using only private cloud resources. You get significantly more breadth and depth of services from public cloud providers because they have so many more resources to scale, improve, and expand their offerings. You also get more innovation, access to a global community, and operational expertise.

Next, we discuss some other significant differences.

Public and private cloud infrastructure

Public cloud providers offer a range of infrastructure options at scale. They store infrastructure in data centers around the world. You can access customized resources for specific geographies and computing needs. Public clouds are multi-tenant, meaning multiple organizations share the same underlying hardware. Each organization’s shared resources exist in a logically isolated tenant on that hardware. Some public cloud resources offer single-tenant hardware options for a physically isolated option.

Private clouds use a single-tenant model, where the infrastructure is dedicated to a single organization. The organization has physically isolated hardware.

The sole focus of a public cloud provider is to maintain and manage infrastructure to strict standards, with multiple configurations and options, to serve a wide range of customers. Organizations using a private cloud generally have different priorities and want to maintain and update their infrastructure according to specific criteria.

Cloud security

A private cloud security strategy depends on the deployment model. Organizations that own and host on-premises infrastructure are responsible for the physical security of the infrastructure they purchase. However, a private cloud does not have to be an on-premises data center. A private cloud can also be in an off-site data center, where your owned infrastructure sits alongside other customers and is maintained by the facility owner, who takes care of the physical security.

You can also deploy private clouds on infrastructure that a third-party organization purchases and maintains in its data center. This is sometimes known as a hosted private cloud. For example, you can maintain a private cloud within a public provider by renting dedicated hosts (bare-metal servers dedicated solely to your company). This provides hardware-level isolation, which is distinct from the software-level isolation of a Virtual Private Cloud (VPC). In hosted private clouds, security of the physical infrastructure is the responsibility of the third party. In all cases, private cloud users are responsible for securing their data and cloud environment from unauthorized access.

In public clouds, security typically follows a shared responsibility model between the cloud provider and the public cloud users. The public cloud provider is responsible for securing all hardware and software infrastructure they provide. You are responsible for data security and the security of your applications in the cloud.

Read about the AWS Shared Responsibility Model »

Deployment

Private cloud deployments can be complex and time-consuming. They can require a significant upfront investment in infrastructure and human resources. You must source teams with domain-specific knowledge and engineering expertise to set up your private cloud environment.

In contrast, public cloud deployments are fast and easy. The cloud service provider often has a graphical UI or command line interface that team members can use to set up and manage the environment. You have various pricing models to choose from, such as on-demand, reserved, or spot instances. You often get to try the services for free before committing to scale.

Ongoing costs

The private cloud model can be more costly over time. You have to maintain and manage your private infrastructure. IT hardware, such as servers and disk storage, needs cooling, electricity, and ongoing physical security. You will also need IT professionals to upgrade system software. New hardware requires up-front purchasing. For example, you might have to purchase extra servers each time your business expands.

In contrast, public cloud resources can offer lower upfront costs and better cost efficiency for variable workloads. You’re purchasing services rather than the hardware on which those services run. There are no maintenance costs, and you only pay for what you use.

Public cloud computing services are preferable in most use cases. They can provide all the underlying software and hardware infrastructure so you can focus on your application development rather than on its development and testing environment.

Public cloud computing services can also be serverless. This means you can build and run applications and services without managing infrastructure. Your application still runs on servers, but the third-party service provider does all the server management.

A private cloud deployment model is typically only suitable for very large organizations that already have multiple data centers and existing infrastructure management systems in place. They use private clouds to improve existing resource utilization. Even then, some such organizations prefer a multicloud or hybrid cloud solution. They use specialized software to seamlessly move workloads between private and public cloud computing resources as needed.

A hybrid cloud deployment integrates a company’s internal IT resources with third-party cloud provider services and infrastructure. With a hybrid cloud, you can store your data and run your applications across multiple environments to meet your specific requirements. You can also centrally provision, scale, and manage all your computing resources.

This environment allows for "cloud bursting," a setup where an organization runs its steady workloads in a private cloud but "bursts" into the public cloud during temporary spikes in traffic, such as seasonal retail events.

Read about hybrid clouds »

Public cloud providers offer dedicated tenancies, where you can rent bare metal servers, which are dedicated machines for your organisation. This physical isolation is required for some types of business configurations. Although it is not a true private cloud, this configuration is a type of hosted private cloud. You can also extend public cloud services into your private cloud, through products such as AWS Outposts, which are deployed within your own private infrastructure.

A virtual private cloud is a private cloud that you can deploy within public cloud infrastructure. It’s a networked, isolated environment where an organization can run code, host websites, store data, and perform other tasks that usually need the resources of a traditional data center. The isolation is provided by a virtualized network connected to all your cloud resources. Virtual private clouds give you the convenience and scalability of public cloud resources, along with more control and security than regular public clouds.

• Public Cloud Model: Internet-facing applications with unpredictable traffic, software development and testing, and big data analytics.
• Private Cloud Model: Highly regulated workloads or those containing sensitive data (such as for HIPAA or financial regulatory compliance), legacy applications, and strictly governed data residency.
• Hybrid Cloud Model: Gradual cloud migrations, handling temporary or seasonal traffic spikes, differing regulatory workloads, and disaster recovery.

	Public cloud	Private cloud
Setup	A cloud provider manages and delivers IT infrastructure over the network for external use.	A single organization manages and delivers IT infrastructure over the network for internal use.
Infrastructure	The scale, variety, and features of resources are very high.	It’s not possible to privately replicate the range and scale of the public cloud. Infrastructure variety is limited.
Security	The cloud provider is responsible for the security of physical and virtual infrastructure. The user is responsible for the security of their data and applications.	The organization is responsible for the security of the hardware and software infrastructure, as well as the data and applications. Offers greater control over sensitive workloads and data sovereignty.
Deployment	Straightforward using API calls, a command line interface, or a few clicks on the graphical UI.	Requires complex technologies and significant IT expertise.
Costs	Pay as you go, no upfront costs. Potentially free for a limited period or a limited usage range. Pricing models include on-demand, reserved, or spot instances.	High initial investment in hardware and software licensing. High ongoing costs for infrastructure maintenance, security, and upgrades.

Amazon Web Services (AWS) offers hundreds of fully featured services from data centers globally. Millions of customers, including the fastest-growing start-ups, largest enterprises, and leading government agencies, use AWS to balance costs, become more agile, and innovate faster.

For example, with AWS as your public cloud provider, you get the following benefits:

• Significantly more services and more features within those services than any other cloud provider.
• Fully managed services in compute, storage, databases, analytics, artificial intelligence and machine learning (AI/ML), Internet of Things (IoT), and more. You can build and run applications for anything you can imagine.
• A flexible and secure cloud computing environment built to satisfy security requirements for the military, global banks, and other high-sensitivity organizations.

For a logically isolated environment for your organization in the cloud, Amazon Virtual Private Cloud (Amazon VPC) gives you full control over your virtual networked environment, including resource placement, connectivity, and security.

Get started with cloud computing on AWS by creating a free account today.