## Contractual open 

Public cloud vendors sometimes productize offerings. Here the user can’t simply create login credentials, provide a credit card, and start using the service. Instead, the user actually signs a contract for service. The term can be as short as a month, or more typically a year. Vendors are also offering public IaaS and PaaS public platforms that are based on a formal contractual basis. 

In this kind of environment, the expectation is for a high level of security, privacy, and governance. These vendors provide a written SLA. Because of the service and security guarantees of this model, some customers may be willing to store critical data in the cloud. 

## Public/private hybrid clouds 

Companies often want the flexibility of the cloud but with the security and predictability of the data center. In these cases, a private cloud provides an environment that sits behind a fire- wall. Unlike a data center, a private cloud is a pool of common resources optimized for the use of the IT organization. Unlike a public cloud, a private cloud adheres to the company’s security, governance and compliance requirements. Whatever service level is required for the company applies to the pri- vate cloud. 

There are two different types of private clouds: 

✓ A private cloud owned and managed by a company for the benefit of its employees and partners 

✓ A commercial private cloud resides in a vendor’s data center and provides a secure connection to the customer’s other IT resources. This approach securely augments a customer’s IT environment. 

In some instances, companies use a combination of public and private cloud services. A retail company may have a private cloud to support its highly distributed development 

