A deployment model describes who owns and uses the cloud infrastructure, as opposed to the service model, which describes which layers you manage. The same IaaS service could be delivered from a public cloud or from a private cloud in your own data center.
A public cloud is run by a provider and shared by many unrelated customers (tenants) over the internet. You get fast self-service provisioning, huge scale and pay-as-you-go billing, with no hardware to buy. A private cloud serves a single organization. It can sit on premises or be hosted by a third party, but it still offers cloud characteristics: self-service, pooled resources, elasticity and metered use. Simply owning virtualized servers is not a private cloud unless users can provision resources on demand. Private clouds suit strict control, special hardware or data that policy says must stay in a particular facility, at the cost of capital expense and limited scale.
A hybrid cloud connects a private cloud or on-premises environment with a public cloud so workloads and data can move or work together, usually over a VPN or dedicated link with shared identity. Common reasons are keeping a sensitive database on premises while web tiers run in the public cloud, or cloud bursting, where extra demand overflows to the public cloud during peaks. A community cloud is shared by several organizations with common requirements, such as government agencies or research institutions that must meet the same compliance rules, and the cost is split among them.
Multicloud means using services from two or more public cloud providers. It is different from hybrid: hybrid is about mixing private and public, multicloud is about mixing providers. Organizations choose multicloud to avoid vendor lock-in, to use a best-of-breed service from each provider, or to meet resilience or regulatory needs. The costs are more skills to maintain, different identity and networking models, harder cost reporting and data egress charges when data moves between providers.
Key terms
- Public cloud
- Cloud infrastructure owned by a provider and shared by many tenants, consumed on demand over the internet.
- Private cloud
- Cloud infrastructure dedicated to one organization, on premises or hosted, that still offers self-service and elasticity.
- Hybrid cloud
- A combination of private or on-premises infrastructure and public cloud, connected so workloads can interoperate.
- Community cloud
- Cloud infrastructure shared by several organizations with common mission, security or compliance needs.
- Multicloud
- Using services from more than one public cloud provider.
- Cloud bursting
- Sending overflow demand from a private environment to a public cloud when local capacity runs out.
A hospital keeps its patient records system in an on-premises private cloud for regulatory reasons, runs its public appointment website in a public cloud, and links the two with a site-to-site VPN. That is a hybrid cloud. When it later adds a second provider's analytics service, it also becomes multicloud.
Check yourself
Several state agencies share infrastructure built to meet the same compliance rules. Which deployment model is this?
A community cloud, because it is shared by organizations with common requirements.
What is the main reason organizations give for adopting multicloud?
Avoiding vendor lock-in, along with using the best service from each provider and adding resilience against one provider's outage.