Difference Between Public Cloud and Private Cloud

Cloud computing is a way of providing IT infrastructure to customer, it is not just a set of product to be implemented. For any service to be a cloud service, the following five criteria need to be fulfilled –

1. On demand self-service : Decision of starting and stopping of service depends on customers without direct interaction with providers.

2. Broad Network Access : Service must be available to any device using any network.

3. Resource Pooling: Provider create a pool of resources and dynamically allocate it to customers.

4. Rapid Elasticity : The services provided by provider must be easily expandable and quick.

5. Measured Services : Provider must measure the usage of service and charge it accordingly. Tracking of usage is also helpful in improving services.

1. Public Cloud : 

Computing in which service provider makes all resources public over the internet. It is connected to the public Internet. Service provider serves resources such as virtual machines, applications, storage, etc to the general public over the internet. It may be free of cost or with minimal pay-per-usage. It is available for public display, Google uses the cloud to run some of its applications like google docs, google drive or YouTube, etc. 

It is the most common way of implementing cloud computing. External cloud service provider owns, operates and delivers it over the public network. 

It is best for the companies which need an infrastructure to accommodate large number of customers and working on projects which has diverse organisation i.e. research institution and NGO etc. 

2. Private Cloud : 

Computing in which service provider makes all resources public over the internet. It only supports connectivity over the private network. It has only authentic users and single-occupant architecture. Google back-end data of the applications like Google Drive, Google docs or YouTube, etc is not available to the public, these types of data and applications run on a private cloud. 

The infrastructure and services are maintained and deployed over a private network; hardware and software are dedicated only to a private company i.e. members of the special entity . 

It is best for the companies which need an infrastructure which has high performance, high security and privacy due to it’s best adaptability and flexibility. 

Below is a table of differences between Public Cloud and Private Cloud:

Public Cloud	Private Cloud
Cloud Computing infrastructure shared to public by service provider over the internet. It supports multiple customers i.e., enterprises.	Cloud Computing infrastructure shared to private organization by service provider over the internet. It supports one enterprise.
Multi-Tenancy i.e., Data of many enterprise are stored in shared environment but are isolated. Data is shared as per rule, permission and security.	Single Tenancy i.e., Data of single enterprise is stored.
Cloud service provider provides all the possible services and hardware as the user-base is world. Different people and organization may need different services and hardware. Services provided must be versatile.	Specific hardware and hardware as per need of enterprise are available in private cloud.
It is hosted at Service Provider site.	It is hosted at Service Provider site or enterprise.
It is connected to the public internet.	It only supports connectivity over the private network.
Scalability is very high, and reliability is moderate.	Scalability is limited, and reliability is very high.
Cloud service provider manages cloud and customers use them.	Managed and used by single enterprise.
It is cheaper than private cloud.	It is costlier than public cloud.
Security matters and dependent on service provider.	It gives high class of security.
Performance is low to medium.	Performance is high.
It has shared servers.	It has dedicated servers.
Example : Amazon web service (AWS) and Google AppEngine etc.	Example : Microsoft KVM, HP, Red Hat & VMWare etc.