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What is Cloud Computing? Many people don't know much about cloud computing. In order to let everyone know more about cloud computing, I summarized the following contents for everyone and looked down together.

The word cloud computing is believed to be very familiar to everyone. As a hot technology in IT industry, it frequently appears in news reports of major media. Internet companies like BAT often put it on their lips. I believe many people want to learn cloud computing and keep up with technology trends. If you have some understanding of cloud computing, you should hear these terms more or less-OpenStack, Hypervisor, KVM, Docker, K8S... All these terms belong to the category of cloud computing.

For self-taught beginners, it is not easy to understand the specific meanings of these nouns and the relationships between them. Although there is a lot of information on the Internet, but messy, obscure, very unfriendly to newcomers, easy to make people confused, or even retreat. Therefore, Xiaobian today's article, as the first lesson of cloud computing, will give you an easy-to-understand macro introduction, focusing on explaining the most important terms and the relationship between them, hoping to help you get started.

What is Cloud computing

Before I get into the weird terms, let me give you a quick introduction to cloud computing.

Before computers were invented, there was no network, and each computer (PC) was a stand-alone computer.

This stand-alone, including CPU, memory, hard disk, graphics and other hardware. Users install operating system and application software on a single machine to complete their work. Later, there was a network (Network), between stand-alone and stand-alone, can exchange information, work together. Later, the stand-alone performance became stronger and stronger, and there was a server. It was found that some servers could be centralized and placed in the computer room, and then users could access and use the computer resources in the computer room through the network.

Then the small network became the big network, and there was the Internet. When a small computer room becomes a large computer room, there is an IDC (Internet Data Center).

When more and more computer resources and application services (such as watching web pages, downloading movies) are centralized, it becomes "cloud computing." Countless large computer rooms become "clouds."

cloud computing

Is it too easy? Slow down, let's go deeper. Cloud computing is simple, to put it bluntly, is to concentrate computer resources on the network. However, the way cloud computing is implemented is complicated.

For example, if you just set up a server in the company's small computer room, open an FTP download service, and then use it for movie sharing among several colleagues, of course, it is very simple.

If it is "Double 11" Taobao Shopping Festival, billions of users around the world visit Alibaba's Taobao website, dozens of PB (1PB=1024TB=1024×1024GB) visits per day, hundreds of GB of traffic per second... This is not a few network cables and several servers can solve. It is necessary to design a cloud computing system with super large capacity, super high concurrency (simultaneous access), super fast speed and super security to meet the requirements of smooth operation of the business. This is the complexity of cloud computing.

As mentioned earlier, we put computer resources in the cloud. This computer resource, in fact, is divided into several levels:

The first level is the lowest level of hardware resources, mainly including CPU (computing resources), hard disk (storage resources), and network card (network resources).

The second level, to be more advanced, I do not intend to directly use the CPU, hard disk, network card, I hope you put the operating system (such as Windows, Linux) installed, the database software installed, I will use.

The third level, more advanced, you not only have to install the operating system these basic, but also the specific application software installed, such as FTP server software, online video server software, etc., I can directly use the service.

These three levels are IaaS, Paas and SaaS, which we often hear.

SaaS: Software as a Service

PaaS: Platform-as-a-Service

IaaS: Infrastructure-as-a-Service

Another picture may be more intuitive:

At present, mainstream cloud computing service providers, such as Amazon AWS, Alibaba Cloud and Huawei Cloud, all provide the above three levels of cloud resources for everyone. Whatever you want, they provide.

How do Ali and Huawei provide such diversified and multi-level cloud computing services? Could it be that it was arranged manually? If you want an eight-core CPU, 16GB memory, 500GB hard disk server, Ali temporarily arranges engineers to help you assemble it? If you want to install CentOS 7.2 (a Linux-like operating system), MySQL 5.5.60 (a database system), Ali also temporarily let engineers help you install configuration? This was obviously impossible. He couldn't afford to waste manpower or wait for time. Therefore, there are various software and platforms responsible for the invocation and management of resources.

What is virtualization?

If you want to manage physical resources, the first step is "virtualization." Virtualization is the foundation of cloud computing. Virtualization is simply running multiple "virtual servers" on a single physical server. This virtual server is also called a virtual machine (VM). On the surface, these virtual machines are independent servers, but in fact, they share the CPU, memory, hardware, network cards and other resources of the physical server.

The physical machine is usually called "host machine". Virtual machines are called "guest machines."

Who does the work of virtualizing physical resources?

The famous Hypervisor.

Hypervisor, translated from Chinese, is "super supervisor", also known as VMM (Virtual Machine Monitor). It is not a specific software, but a general term for a class of software.

Hypervisors fall into two broad categories:

In the first category, the hypervisor runs directly on top of the physical machine. Virtual machines run on top of hypervisors. In the second category, a normal operating system (such as Linux or Windows) is installed on the physical machine, and then a hypervisor is installed on the normal operating system to generate and manage the virtual machine. VMware, KVM, Xen, Virtual Box, all belong to Hypervisors. VMware should be familiar to everyone, it is VMware Workstation. To learn Linux, many people install WMware under Windows and then create Linux virtual machines.

But the real thing is KVM (kernel-based virtual machine). It is currently the hottest and most sought after virtualization solution.

Hypervisor software such as KVM actually provides a virtualization capability that simulates CPU operation and is more low-level. But its user interaction is not good, inconvenient to use.

Therefore, in order to better manage virtual machines, cloud management platforms such as OpenStack are needed. I have talked about OpenStack before (link). It's kind of like a store that manages goods (compute resources, storage resources, network resources, etc.) and sells them to users, but it doesn't make goods itself (it doesn't have virtualization capabilities), its goods come from KVM. Of course, if you don't use KVM, you can also use other hypervisors such as Xen.

OpenStack management interface, much better than the command line, right?

Keep in mind that several of the concepts mentioned above, including VM, KVM, OpenStack, etc., are primarily IaaS (Infrastructure as a Service). Is that understandable?

Containers VS Virtual Machines

So, containers, Docker, K8S, what are they?

According to the virtualization method mentioned above, after using it for a while, people found that it has some problems:

Different users sometimes just want to run their own simple programs, running a small process. In order not to interfere with each other, virtual machines must be established. If you build a virtual machine, obviously the waste will be a little big, and the operation is more complicated, and it will take a long time.

And, sometimes, to migrate your own services, you have to migrate the entire virtual machine. Obviously, the migration process can be complicated. Is there a way to be more flexible and faster? Yes, this introduces "containers."

Containers are also virtualized, but are "lightweight" virtualization. Its purpose, like virtual machines, is to create "isolated environments." However, it is very different from virtual machines-virtual machines are operating system level resource isolation, while containers are essentially process level resource isolation.

Docker, which we often hear about, is a tool for creating containers, an application container engine.

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