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Getting started with Docker

Debut: arppinging

What is Docker?

Docker is not only a container technology, but also a kind of virtualization technology.

1) Virtualization Technology Classification 1.1 Host level Virtualization

There are two types of host-level virtualization, Type- Ⅰ and Type- Ⅱ, which are described below.

1.1.1 Type- Ⅰ

Host-level virtualization of Type- Ⅰ installs virtualized operating systems, such as Vmware's ESXi, directly on physical hardware, and then installs virtual machines on the virtualization layer.

1.1.2 Type- Ⅱ

Type- Ⅱ host-level virtualization: install virtualization software, such as vmware workstation, on top of the existing operating system, and then create the operating system on the virtualization software.

1.2 Container-level virtualization

It can be seen that in container-level virtualization, there is no independent operating system kernel in the container, and the container is deployed directly on the host operating system.

1.3 advantages and disadvantages of several virtualization technologies

1. Type- Ⅰ virtualization: each virtual machine has its own independent system kernel, which can interact with the hardware directly through the virtualization layer.

2. Type- Ⅱ Virtualization: each virtual machine has its own independent operating system, which adds a layer of virtualization software compared to type- Ⅰ, while the virtualization software itself may have security risks.

3. Container-level virtualization: in container-level virtualization, all containers share a kernel, which is not as thorough as host-level virtualization in terms of isolation.

2) advantages of Docker

1. Docker containers start quickly, and most docker containers only take less than 1 second to start.

2. Docker modeling is simple and fast, and users can "docker" their programs in a few minutes.

3. To make the logical separation of responsibilities, developers only need to care about the applications running in the container, while operators only need to care about how to manage the container.

4. Fast and efficient development life cycle, docker has high portability.

5. Docker makes distributed application deployment more important.

II. Docker component 1) Docker client and server

Docker is a Cramp S architecture program, the Docker client only needs to make a request to the server or daemon, and the server or daemon will do all the work and return the result.

The client and server can be on the same server or on different machines. You can think of the server as a nginx service and the client as a web browser.

2) Docker image

Mirroring is the cornerstone of Docker. Users run the container based on the image. Images are similar to ova files that can be imported into vmware workstation to run, except that docker images only need to be created and run, and there is no need to build the system kernel again. The image is the "source code" of the container, which is small and easy to share and update.

3) Registry

Registry is a repository for storing images. Registry is divided into public and private. The public Registry operated by Docker is called Docker Hub, and the private one is generally the image repository within the company.

4) Container

The container is started based on an image, and one or more processes can be run in the container. You can think of an image as the build or packaging phase of the Docker lifecycle, while the container is the startup or execution phase.

If the image is similar to an OVA file, then the container is similar to importing the OVA file into vmware workstation and clicking on the running status.

Each container contains an image, and if you think of the container as a container (shown in a truck below), then the image is the goods inside.

Images can be created, started, shut down, restarted, and destroyed, similar to loading and unloading. Docker doesn't care what's inside the container. It's a web service. Or a database? Whatever it is, docker will be "loaded" according to a uniform standard.

To sum up, the Docker container is:

An image format, a series of standard operations, an execution environment.

The docker container is also very easy to move, so we can transfer it to the image repository and run it anywhere and on the machine. III. Technical components of Docker

Docker can run on any host with 64bit Linux installed, and the docker overhead is low, but the following features should also be supported on the host:

3.1A native Linux container format

Docker is called libcontainer. Because no matter what the image is, docker is loaded in the same format.

3.2 Namespace (namespace) of the Linux kernel

Because all containers on a server share a kernel, some problems may arise if the containers are not independent. For example, port 80 is required for two containers running nginx.

This can lead to preemption, making the service unavailable.

Namespaces can independently separate the following resources:

1.UTS: hostname and domain name

2.IPC: semaphores, message queues, and shared memory

3.PID: process number

4.Network: network devices, network stacks, ports, etc.

5.Mount: Mount point

6.User: users and user groups

3.3Resource isolation and grouping (cgourps)

Control group,cgroups can allocate hardware resources such as cpcu and memory to each docker container independently.

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