Cloud computing Concept

Baidu encyclopedia definition: cloud computing is an Internet-based service increase, use, and delivery model. It usually involves providing dynamic and scalable resources through the Internet and is often virtualized.
Personal Understanding: Share computing resources through the network, and provide infrastructure, platform, software and other services to the customer by leasing, in order to obtain the corresponding use fee.
The transformation brought about by cloud computing is to shift the company's capital expenditure (purchase of machines) to operational expenditure (use cost). In the early deployment phase of the system, this change is very cost-effective.
Cloud Computing Features:

Elasticity and scalability: computing resources can be freely expanded or reduced based on the system scale and usage requirements;
Billing by usage: the billing method may be based on storage capacity or bandwidth traffic;
Select services as needed: Build a system based on the cloud environment and focus on your own business logic. The services on which the system depends can be obtained from the cloud, this pluggable application model makes it easier to build a large-scale application system. Instagram has only 13 employees and has created $1 billion in value by relying on the cloud services provided by Amazon;
Multi-tenant: A cloud environment can carry multiple systems for deployment, and systems can be isolated from each other, without affecting each other.
Failover: When the encapsulated service machine fails, the service can be migrated to other machines without affecting user usage. The migration process is transparent to users.
Cloud Service Model:

SAAS (sofeware as a Service)-software as a service
The frontend cloud service model that users can access
The service provider builds the software and the cloud environment, and the customer does not need to pay attention to the background deployment of the software. The customer can connect to and use the software through the client, and pay by usage.
Well-known SaaS providers, such as foreign Salesforce (a global leader in On-Demand CRM solutions) and eight hundred customers in China, all provide services to customers by deploying CRM applications on the cloud.

PAAs (platform as a Service)-platform as a service
Unlike SaaS applications, Paas provides users with a development platform instead of a specific application. developers can deploy their own system applications on this platform, the infrastructure services provided by the platform (such as storage and Database) can also be referenced to accelerate the construction of the system.
Well-known PAAs platforms include Google's App Engine, Salesforce's force.com, and open-source cloudfoundry (known as Linux in the cloud era)

IAAs (Infrastructure as a Service)-infrastructure as a service
Before deploying system applications, we need to purchase machines, install operating systems, and build networks...
In the cloud environment, these resources are completely managed by service providers and used by users by leasing. These infrastructures are collectively referred to as IAAs.
Amazon EC2 is a typical IAAs application. by leasing its storage, network, processor, and other infrastructure, you can get the usage fee.

Compared with traditional system applications, IAAs is equivalent to physical hardware, Paas is equivalent to the operating system, and SAAS is equivalent to software installed on the operating system.
SAAS is mostly for consumers, while Paas is mostly for developers. IAAs is mainly managed by service providers and completely transparent to users. Therefore, from the perspective of users, SAAS is the closest, Paas is the most controllable, and IAAs is the most abstract.
Cloud deployment model:

Public cloud: open to all users
Public Clouds usually refer to the clouds that users of third-party providers can use. Public clouds are generally available over the Internet and may be free or cost-effective. This cloud has many instances that can provide services in today's open public network.

Private cloud: open to enterprise users
Private cloud is located within the company's firewall and managed by the enterprise. They are cloud services created and controlled within an enterprise, which greatly guarantees security.

Industry cloud: Build a cloud environment with specific features for specific industries

Hybrid cloud: Two or more cloud Environments