Apart from differences that exist in the cloud paradigms and should be taken under consideration by pubic bodies, a major decision is the deployment model of the cloud. Cloud hosting deployment models are mainly distinguished by the proprietorship and accessibility of the infrastructure, but also by the purpose and the nature of the cloud. Therefore, before investing on cloud, public administrations should be well aware of the deployment models and select the appropriate based on the requirements of the services to be deployed.

There are two main types of cloud; public and private, but there are three more models that are also possible to be used by public bodies; virtual private cloud, hybrid and community cloud.

Public Cloud: is a type of cloud hosting in which the cloud services are delivered over a network which is open for public usage. This model is a true representation of cloud hosting; in this the service provider renders services and infrastructure to various clients. The customers do not have any distinguishability and control over the location of the infrastructure.

Private Cloud: is also known as internal cloud; the platform for cloud computing is implemented on a cloud-based secure environment that is safeguarded by a firewall which is under the governance of the IT department that belongs to the particular corporate.

Virtual Private Cloud: is an on-demand configurable pool of shared computing resources allocated within a public cloud environment, providing a certain level of isolation between the different organizations using the resources[1].

Hybrid Cloud: can be an arrangement of two or more cloud servers, i.e. private, public or community cloud that is bound together but remain individual entities.

Community Cloud: is a type of cloud hosting in which the setup is mutually shared between many organisations that belong to a particular community

Based on our experience we have concluded on the following best practices and factors that should be taken under account.

It is important to find the right balance between control and convenience. With public clouds, there is no need to worry about certain things like maintenance, but controllability is limited. With private clouds, more freedom is offered and a public administrator is responsible on how everything works.

Public cloud is better suited for applications that have more frequent peak times. A public cloud benefits on the decreased capital overheads that a service with spikes on the usages needs.

Scalability and flexibility of public clouds is considered to be greater. Private clouds can achieve high scalability and flexibility standards, as public clouds do, but a lot of investment is needed.

Private cloud gives the organisation greater and direct control over their data, as the organization is managing everything and as data can be more safe as it is not publicly available.

Highly sensitive materials usually are stored to private cloud. This is because as much as public clouds are somewhat secure; your data could still fall in the wrong hands[2].

Although private cloud is generally preferred regards to security and data privacy, in case of natural disaster and internal data theft the private cloud may be prone to vulnerabilities[3].

Private cloud is better suited for public organizations that may change their needs, organizations that have restricted management demands, host mission critical services, and in general prefer to have fully control of their services and infrastructure.

Hybrid cloud is ideal for utilizing the benefits of both the private and public deployment models. A typical example is increasing the capacity of the cloud by aggregating different cloud offerings or services.

In hybrid cloud solutions, resources that are non-critical like development and test workloads can be housed in the public cloud that belongs to a third-party provider, while the workloads that are critical or sensitive can be housed internally. During the piloting period of STRATEGIC, we utilized hybrid based scenarios, as applications were deployed initially in public cloud of Amazon.

If high demand on resources is needed, hybrid cloud can be utilized in order to support cloud bursting and allow public cloud to serve specific instances.

Community cloud can be used by public bodies in order to share common resources and have great savings on the cost of the cloud. This is possible as public bodies generally have similar privacy, performance and security concerns. A community cloud may be internally managed or it can be managed by a third-party provider. It can be hosted externally or internally[4].

For Virtual Private Clouds, the isolation of the organization can be achieved through allocation of a private IP subnet and a virtual communication construct such as a VLAN. This case was tested by STRATEGIC for the pilot of MoSG.

[1] http://blog.unitedlayer.com/cloud-computing-terminologies