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Docker overview
Docker is an open source application container engine that allows developers to package their applications and dependencies into a portable image, and then publish it to any popular Linux or Windows operating system machine, and can also implement virtualization. Containers use a sandbox mechanism completely, and there will be no interfaces between them.
Essence: All technologies are learned because of some problems that we need to solve.
Docker is developed based on the Go language. For details, you can check the official website of Docker to understand and learn.
Docker Official WebsiteDocker
DocumentationDocker
Mirror Warehouse
What can Docker do?
virtual machine technology
Disadvantages of virtual machine technology:
- Very resource intensive
- Many redundant steps
- start very slow
container technology
Containerization is not a simulation of a full operating system
Compare the difference between Docker and virtual machine technology:
- A traditional virtual machine virtualizes a piece of hardware, runs a complete operating system, and then installs and runs software on this system.
- The application in the container runs directly in the kernel of the host machine. The container does not have its own kernel, nor does it virtualize our hardware, so it is portable.
- Each container is isolated from each other, and each container has its own file system, which does not affect each other.
Devops (development, operation and maintenance)
Faster delivery and deployment of applications
Traditional: a bunch of help documents, installers.
Docker: Package image release test, run with one click.
Easier upgrade and expansion
After using Docker, we deploy applications just like building blocks.
The project is packaged as a mirror image, which can be expanded horizontally.
Easier system operation and maintenance
After containerization, our development and test environments are highly consistent.
More efficient use of computing resources
Docker is kernel-level virtualization, which can run many container instances on a physical machine, and the performance of the server can be squeezed to the extreme.
Docker installation
The basic composition of Docker
Image:
Docker image is like a template through which container services can be created, tomcat image —> run —> tomcat01 container (providing server), multiple containers can be created through this image (final service operation or project run in the container).
Container (container):
Docker uses container technology to run one or a group of applications independently and create them through mirroring.
Containers can be started, stopped, and deleted.
At present, this container can be understood as a simple linux system.
Warehouse (repository):
The warehouse is the place where the image is stored. The warehouse is divided into public warehouses and private warehouses.
Docker Hub (foreign by default), Alibaba Cloud, NetEase Cloud, etc. all have container servers (configured with mirror acceleration).
Install Docker
Environment preparation:
- A little basic knowledge of Linux is required
- CentOS 7
- Use Xshell to connect to the remote server for operation (here I am using VMware)
Environment view:
uname -r
cat /etc/os-release
# 系统内核是3.10以上
[root@wyc /]# uname -r
3.10.0-1160.el7.x86_64
# 系统版本
[root@wyc /]# cat /etc/os-release
NAME="CentOS Linux"
VERSION="7 (Core)"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="7"
PRETTY_NAME="CentOS Linux 7 (Core)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:7"
HOME_URL="https://www.centos.org/"
BUG_REPORT_URL="https://bugs.centos.org/"
CENTOS_MANTISBT_PROJECT="CentOS-7"
CENTOS_MANTISBT_PROJECT_VERSION="7"
REDHAT_SUPPORT_PRODUCT="centos"
REDHAT_SUPPORT_PRODUCT_VERSION="7"
Install:
1. Uninstall the old version
# 卸载旧版本
yum remove docker \
docker-client \
docker-client-latest \
docker-common \
docker-latest \
docker-latest-logrotate \
docker-logrotate \
docker-engine
2. Required installation packages
# 需要的安装包
yum install -y yum-utils
3. Set up a mirrored warehouse
# 设置镜像的仓库
yum-config-manager \
--add-repo \
https://download.docker.com/linux/centos/docker-ce.repo # 默认是从国外的
yum-config-manager \
--add-repo \
http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo # 推荐使用阿里云的
# 安装容器之前，更新 yum 软件包索引
yum makecache fast
4. Install container-related docker-ce (community edition) and docker-ee (enterprise edition)
# 安装容器相关的 docker-ce
yum install docker-ce docker-ce-cli containerd.io docker-compose-plugin
5. Start docker
# 启动 docker
systemctl start docker
6. Use docker version to check whether the installation is successful
# 查看是否安装成功
docker version
[root@wyc /]# docker version
Client: Docker Engine - Community
Version: 20.10.21
API version: 1.41
Go version: go1.18.7
Git commit: baeda1f
Built: Tue Oct 25 18:04:24 2022
OS/Arch: linux/amd64
Context: default
Experimental: true
Server: Docker Engine - Community
Engine:
Version: 20.10.21
API version: 1.41 (minimum version 1.12)
Go version: go1.18.7
Git commit: 3056208
Built: Tue Oct 25 18:02:38 2022
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: 1.6.9
GitCommit: 1c90a442489720eec95342e1789ee8a5e1b9536f
runc:
Version: 1.1.4
GitCommit: v1.1.4-0-g5fd4c4d
docker-init:
Version: 0.19.0
GitCommit: de40ad0
7. Verify that docker is installed correctly
seeHello from Docker!It is correctly installed!
# 验证 docker 是否安装正确
docker run hello-world
[root@wyc /]# docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
2db29710123e: Pull complete
Digest: sha256:faa03e786c97f07ef34423fccceeec2398ec8a5759259f94d99078f264e9d7af
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
(amd64)
3. The Docker daemon created a new container from that image which runs the
executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it
to your terminal.
To try something more ambitious, you can run an Ubuntu container with:
$ docker run -it ubuntu bash
Share images, automate workflows, and more with a free Docker ID:
https://hub.docker.com/
For more examples and ideas, visit:
https://docs.docker.com/get-started/
8. View the downloaded hello-world image
# 查看下载的 hello-world 镜像
docker images
[root@wyc /]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-world latest feb5d9fea6a5 13 months ago 13.3kB
Uninstall Docker:
# 1. 卸载依赖
yum remove docker-ce docker-ce-CLI container d . io docker-compose-plugin
# 2. 删除资源
rm -rf /var/lib/docker # docker的默认工作路径
rm -rf /var/lib/containerd
Alibaba Cloud Mirror Acceleration
1. Log in to Alibaba Cloud and find the container image service
Position is a column in flex compute
2. Find the image acceleration address
3. Configuration acceleration
sudo mkdir -p /etc/docker
sudo tee /etc/docker/daemon.json <<-'EOF'
{
"registry-mirrors": ["https://72ixx83s.mirror.aliyuncs.com"]
}
EOF
sudo systemctl daemon-reload
sudo systemctl restart docker
Run process and Docker principle
Flowchart of Run
underlying principle
How does Docker work?
Docker is a system of Client-Server structure. The Docker daemon process runs on the host and is accessed from the client through Socket. DockerServer will execute the command after receiving the command from Docker-Client.
Why is Docker faster than VM?
1. Docker has fewer abstraction layers than virtual machines
2. Docker uses the kernel of the host machine, and vm needs to be a Guest OS (that is, the virtual machine operating system in the figure below)
Therefore, when creating a new container, Docker does not need to reload an operating system kernel like a virtual machine to avoid booting. The virtual machine loads the Guest OS at the minute level, while Docker uses the host's operating system, omitting this complicated process, at the second level.
Other Differences Between Docker and VMs:
Sense Read! Please correct me if you have any questions!
Reference source: [Mad God Talks about Java] Docker's latest ultra-detailed tutorial is easy to understand