Clouds are virtualised resources, easily accessible. They’re:
Scaleable: Can be dynamically reconfigured to adjust for variable load. E.g. more resources can be allocated while many people are accessing it.
Elastic: CPU and other utilisation is optimised
They use pay-per-use models.
Virtualised Infrastructure
Provides cloud services that can be moved between machines between datacenters seamlessly.
Layers
Software as a Service: User-focused Cloud Drives, etc.
Platform as a Service: AWS, Azure, VPSs
Infrastructure as a Service: Data centers, Hypervisors
A typical Cloud Stack
Hypervisor
Hypervisors allow multiple virtual machines to run on a single physical machine. A VPS would run on a single hypervisor provided by the Infrastructure provider, but it may be migrated to another datacenter seamlessly if necessary.
Virtual Infrastructure Managers
VIMs integrate image, network and virtualisation. Example: OpenStack
