Docker学习笔记--CLI和Registry

Docker概览

Docker架构

Docker采用client-server架构，client和daemon间使用REST API进行通讯。client和daemon可以运行在相同或不同的机器。daemon间也可以通过Docker API通讯。

Docker Registry存储image，Docker Hub和Docker Cloud是两个公有Registry，默认使用Docker Hub，也可以配置使用私有的Registry。
使用Docker时会涉及image、container、network、volume、plugin等对象。

• Image是用来创建Container的只读模板。一个Image可以建立在另一个Image之上，使用Dockerfile文件配置image。Dockerfile的每一指令创建一个image layer，当更改Dockerfile重建image时，仅更改的layer被重建。
• Container是Image的运行实例。

Docker版本

• Community Edition (CE)
• Enterprise Edition (EE)

Capabilities	Community Edition	Enterprise Edition Basic	Enterprise Edition Standard	Enterprise Edition Advanced
Container engine and built in orchestration, networking, security	yes	yes	yes	yes
Certified infrastructure, plugins and ISV containers		yes	yes	yes
Image management			yes	yes
Container app management			yes	yes
Image security scanning				yes

自17年3月，Docker版本号采用YY.mm.patch格式，YY.mm代表年月。

安装和卸载

在CentOS 7或RHEL 7上可直接使用yum安装，如下：

# yum install docker
# systemctl enable docker
# systemctl start docker

docker配置文件位置：
/etc/sysconfig/docker
/etc/docker目录

安装官方最新版本docker，步骤如下：

卸载旧版本

如安装过Docker先卸载，旧版本称为docker或docker-engine，：

# yum remove docker docker-client docker-client-latest docker-common \
           docker-latest docker-latest-logrotate docker-logrotate \
           docker-selinux docker-engine-selinux docker-engine

目录/var/lib/docker/下的内容不会删除，其中包含images、containers、volumes、networks等。

安装Docker CE

1. 更新系统

# yum update

安装最新版的container-selinux

# yum install -y http://mirror.centos.org/centos/7/extras/x86_64/Packages/container-selinux-2.66-1.el7.noarch.rpm

如未更新container-selinux，在安装Docker CE时可能会显示如下错误：

Error: Package: docker-ce-18.06.0.ce-3.el7.x86_64 (docker-ce-edge)
           Requires: container-selinux >= 2.9

2. 安装必须的Package

yum-utils提供yum-config-manager工具，用来配置Docker Repository；devicemapper storage driver需要device-mapper-persistent-data和lvm2

# yum install -y yum-utils device-mapper-persistent-data lvm2

3. 配置Docker Repository

# yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

默认stable repository是启用的，若要启用edge或test repository(stable repository是必须的)，执行如下命令：

# yum-config-manager --enable docker-ce-edge
# yum-config-manager --enable docker-ce-test

4. 安装Docker CE

# yum install docker-ce
# systemctl enable docker
# systemctl start docker

5. 验证docker安装

# docker info
# docker --version
# docker version

运行hello-world：

# docker run hello-world

成功后输出如下：

Unable to find image 'hello-world:latest' locally
Trying to pull repository docker.io/library/hello-world ...
latest: Pulling from docker.io/library/hello-world
1b930d010525: Pull complete
Digest: sha256:2557e3c07ed1e38f26e389462d03ed943586f744621577a99efb77324b0fe535
Status: Downloaded newer image for docker.io/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.

查看image和container：

# docker images
# docker ps

6. 用户管理

Docker Daemon绑定了Unix socket，而不是TCP端口，默认Unix socket由root和sudo权限的用户拥有。为了运行docker命令时不使用sudo，创建Unix group "docker"(Docker安装后创建了docker group)，将用户添加到docker group即可。当docker daemon启动时，让docker group有读/写Unix Socket权限。

# groupadd docker
# usermod -aG docker $USER

执行以上命令后需重新登录或重启。

卸载Docker CE

# yum remove docker-ce

Images、 containers、 volumes、customized configuration files不会自动删除，执行以下命令删除：

# rm -rf /var/lib/docker

Docker CLI

CLI	Description
Engine CLI	The main CLI for Docker, includes all docker and dockerd commands
Compose CLI	The CLI for Docker Compose, which allows you to build and run multi-container applications
Machine CLI	Manages virtual machines that are pre-configured to run Docker
DTR CLI	Deploy and manage Docker Trusted Registry
UCP CLI	Deploy and manage Universal Control Plane

Docke支持多方面的CLI，下面仅涉及Engine CLI docker。

运行不带任何参数的docker命令或docker help，可列出所有可用的docker命令。

为了查看某一命令的帮助，执行如下命令：

$ docker run --help

option参数可以组合在一起：

docker run -i -t --name test busybox sh

可以写成：

docker run -it --name test busybox sh

docker run

$ docker run [OPTIONS] IMAGE[:TAG|@DIGEST] [COMMAND] [ARG...]

启动docker container有两种模式：Detached、Foreground，默认是Foreground模式。
Foreground模式
Options:

-a=[]         : Attach to `STDIN`, `STDOUT` and/or `STDERR`
-t              : Allocate a pseudo-tty
--sig-proxy=true: Proxy all received signals to the process (non-TTY mode only)
-i              : Keep STDIN open even if not attached

-i -t组合在一起使用，可以与容器进行交互：

$ docker run -a stdin -a stdout -i -t ubuntu /bin/bash

运行以上命令后，会执行以下操作：

1. 如本地没有ubuntu image，将从registry获取，相当于手动执行docker pull ubuntu
2. Docker创建新的容器，相当于运行docker container create
3. Docker给容器分配可读写的文件系统
4. Docker创建网络接口连接容器到默认网络
5. Docker启动容器并执行/bin/bash

容器启动后，可以执行shell命令，如下：

root@f7cbdac22a02:/# hostname
root@f7cbdac22a02:/# cat /etc/hosts
root@f7cbdac22a02:/# yum install -y vim

6. 输入exit，终止/bin/bash，容器停止但不会被删除，可以重新启动。

root@f7cbdac22a02:/# exit

Detached模式
当指定-d选项后，启用Detached模式，container将在后台运行。

$ docker run -d -p 80:80 my_image nginx -g 'daemon off;'

Container identification
有三种类型：

Identifier type	Example value
UUID long identifier	“f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778”
UUID short identifier	“f78375b1c487”
Name	“evil_ptolemy”

当运行container时，如未使用--name指定容器名，daemon将生成一随机字符串作为名字。

Attach to and detach from a running container

$ docker run -d --name topdemo ubuntu /usr/bin/top -b
$ docker attach topdemo

docker commit

使用docker commit可以从container创建image。

docker commit [OPTIONS] CONTAINER [REPOSITORY[:TAG]]

Options

Name, shorthand	Default	Description
--author , -a		Author (e.g., “John Hannibal Smith [email protected]”)
--change , -c		Apply Dockerfile instruction to the created image
--message , -m		Commit message
--pause , -p	true	Pause container during commit

先创建一个Container

$ docker run -t -i training/sinatra /bin/bash

然后运行shell脚本更新container

$ root@0b2616b0e5a8:/# yum install vim

更新完毕后，运行exit退出。
最后使用docker commit创建image：

$ docker commit -m "Added json gem" -a "Kate Smith" 0b2616b0e5a8 ouruser/sinatra:v2

还可以使用--change修改后再创建image：

$ docker commit --change='CMD ["apachectl", "-DFOREGROUND"]' -c "EXPOSE 80" c3f279d17e0a  svendowideit/testimage:version4

docker build

从Dockerfile创建image，这是最常用的方式。

docker build [OPTIONS] PATH | URL | -

下面演示从Dockerfile创建image：
Dockerfile
创建一个空目录，在其内创建名为Dockerfile的文件，内容如下：

# Use an official Python runtime as a parent image
FROM python:2.7-slim

# Set the working directory to /app
WORKDIR /app

# Copy the current directory contents into the container at /app
ADD . /app

# Install any needed packages specified in requirements.txt
RUN pip install --trusted-host pypi.python.org -r requirements.txt

# Make port 80 available to the world outside this container
EXPOSE 80

# Define environment variable
ENV NAME World

# Run app.py when the container launches
CMD ["python", "app.py"]

Dockerfile引用了文件app.py 和 requirements.txt，下面在相同目录创建这两个文件：
requirements.txt

Flask
Redis

app.py

from flask import Flask
from redis import Redis, RedisError
import os
import socket

# Connect to Redis
redis = Redis(host="redis", db=0, socket_connect_timeout=2, socket_timeout=2)

app = Flask(__name__)

@app.route("/")
def hello():
    try:
        visits = redis.incr("counter")
    except RedisError:
        visits = "<i>cannot connect to Redis, counter disabled</i>"

    html = "<h3>Hello {name}!</h3>" \
           "<b>Hostname:</b> {hostname}<br/>" \
           "<b>Visits:</b> {visits}"
    return html.format(name=os.getenv("NAME", "world"), hostname=socket.gethostname(), visits=visits)

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=80)

Build

$ docker build -t friendlyhello .

Container相关命令

Command	Description
docker attach	Attach local standard input, output, and error streams to a running container
docker container	Manage containers
docker cp	Copy files/folders between a container and the local filesystem
docker create	Create a new container
docker diff	Inspect changes to files or directories on a container’s filesystem
docker exec	Run a command in a running container
docker export	Export a container’s filesystem as a tar archive
docker kill	Kill one or more running containers
docker logs	Fetch the logs of a container
docker pause	Pause all processes within one or more containers
docker port	List port mappings or a specific mapping for the container
docker ps	List containers
docker rename	Rename a container
docker restart	Restart one or more containers
docker rm	Remove one or more containers
docker run	Run a command in a new container
docker start	Start one or more stopped containers
docker stats	Display a live stream of container(s) resource usage statistics
docker stop	Stop one or more running containers
docker top	Display the running processes of a container
docker unpause	Unpause all processes within one or more containers
docker update	Update configuration of one or more containers
docker wait	Block until one or more containers stop, then print their exit codes

示例：
List containers

$ docker ps -a

-a 显示所有的container，默认仅显示运行的container

Stop one or more running containers

$ docker stop CONTAINER [CONTAINER...]

Remove one or more containers

$ docker rm CONTAINER [CONTAINER...]

Remove all containers

$ docker rm `docker ps -a -q`

Start one or more stopped containers

$ docker start CONTAINER [CONTAINER...]

Fetch the logs of a container

$ docker logs -f --until=2s my_container

Run a command in a running container

$ docker exec -d my_container touch /tmp/execWorks

Image相关命令

Command	Description
docker build	Build an image from a Dockerfile
docker commit	Create a new image from a container’s changes
docker history	Show the history of an image
docker image	Manage images
docker images	List images
docker import	Import the contents from a tarball to create a filesystem image
docker load	Load an image from a tar archive or STDIN
docker manifest	Manage Docker image manifests and manifest lists
docker pull	Pull an image or a repository from a registry
docker push	Push an image or a repository to a registry
docker rmi	Remove one or more images
docker save	Save one or more images to a tar archive (streamed to STDOUT by default)
docker search	Search the Docker Hub for images
docker tag	Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE
docker trust	Manage trust on Docker images

示例：
pull an image

$ docker pull hello-world

Push an image

$ docker push hello-world:latest

List images

$ docker images

Search images

$ docker search centos

Remove one or more images

$ docker rmi IMAGE [IMAGE...]

Remove all images

$ docker rmi `docker images -a -q`

Registry命令

Command	Description
docker login	Log in to a Docker registry
docker logout	Log out from a Docker registry
docker pull	Pull an image or a repository from a registry
docker push	Push an image or a repository to a registry

搭建私有Registry

docker常用命令结构：

docker <command> <registry-hostname>:<registry-port>/<namespace>/<image>:<tag>

默认Registry为Docker Hub，默认namespace为/library，以下三个命令效果相同：

# docker pull hello-world
# docker pull docker.io/hello-world
# docker pull docker.io/library/hello-world

使用Docker中国官方镜像registry.docker-cn.com可以享受到更快的下载速度和更强的稳定性，但只包含流行的公有镜像。

# docker pull registry.docker-cn.com/library/hello-world

可以配置Docker守护进程默认使用Docker中国官方镜像，这样无需在每次拉取时指定registry.docker-cn.com，修改文件/etc/docker/daemon.json添加registry-mirrors键值：

{
  "registry-mirrors": ["https://registry.docker-cn.com"]
}

保存后重启Docker以使配置生效。

初识Registry

1. 使用官方registry镜像创建私有Registry

# mkdir /mnt/registry/docker
# docker run -d -p 5000:5000  --restart always -v /mnt/registry:/var/lib/registry --name registry registry

参数说明：
--restart always 容器异常退出或重启docker后自动重启容器
-v /mnt/registry:/var/lib/registry 绑定/mnt/registry到容器/var/lib/registry目录(存放镜像文件的目录)来实现数据持久化

selinux
如系统启用了selinux，要为/mnt/registry设置selinux安全上下文类型，如下：

# semanage fcontext -a -t container_file_t "/mnt/registry(/.*)?"
# restorecon -R -v /mnt/registry

2. 上传image

为image打标签后上传到仓库：

$ docker tag hello-world localhost:5000/hello-world:latest
$ docker push localhost:5000/hello-world:latest

tag语法：
Usage: docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG]

也可以使用IMAGE ID：

$ docker tag fce289e99eb9 localhost:5000/hello-world:latest

如系统启用了selinux，但未设置安全上下文类型，上传时会一直retry，报如下错误（可运行journalctl -xe查看原因）：

SELinux is preventing /bin/registry from add_name access on the directory docker.

*****  Plugin catchall_labels (83.8 confidence) suggests   *******************

If you want to allow registry to have add_name access on the docker directory
Then you need to change the label on docker
Do
# semanage fcontext -a -t FILE_TYPE 'docker'
where FILE_TYPE is one of the following: container_file_t, container_var_lib_t, nfs_t, svirt_home_t, tmpfs_t, virt_home_t.
Then execute:
restorecon -v 'docker'

3. 从本地registry运行容器

$ docker run localhost:5000/hello-world

4. 查看registry中的image

列出所有image：

curl http://localhost:5000/v2/_catalog

列出hello-world image：

curl http://localhost:5000/v2/hello-world/tags/list

5. 外部访问registry

通过上面方式创建的registry其协议为http，是不安全的，只适用于本地使用，若要从外部访问registry，需要编辑/etc/docker/daemon.json，增加insecure-registries，如下：

{
  "insecure-registries": ["192.168.122.1:5000"]
}

配置完毕后需重启docker。

SSL Registry

1. 获取证书

以自签名证书为例，Registry URL为registry.itrunner.org，生成自签名证书：

$ cd /mnt/registry
$ mkdir certs
$ openssl req -newkey rsa:2048 -nodes -sha256 -keyout certs/domain.key \
-x509 -days 365 -out certs/domain.crt -subj /C=CN/ST=Beijing/L=Beijing/CN=registry.itrunner.org/OU=itrunner/O=itrunner/[email protected]

同样，如系统启用了selinux，需给certs目录指定安全上下文：

# semanage fcontext -a -t container_file_t "certs(/.*)?"
# restorecon -R -v certs

每台使用这个Registry的主机都需将自签名证书拷贝到/etc/docker/certs.d/registry.itrunner.org目录下：

# mkdir /etc/docker/certs.d/registry.itrunner.org
# cp certs/domain.crt /etc/docker/certs.d/registry.itrunner.org

2. 删除当前运行的Registry

$ docker stop registry
$ docker rm registry

3. 配置证书重新运行Registry

$ docker run -d --restart always --name registry -v /mnt/registry:/var/lib/registry \
-v "$(pwd)"/certs:/certs \
-e REGISTRY_HTTP_ADDR=0.0.0.0:443 \
-e REGISTRY_HTTP_TLS_CERTIFICATE=/certs/domain.crt \
-e REGISTRY_HTTP_TLS_KEY=/certs/domain.key \
-p 443:443 \
registry

4. 测试

$ curl -k https://registry.itrunner.org/v2/

$ docker tag hello-world registry.itrunner.org/hello-world
$ docker push registry.itrunner.org/hello-world
$ docker pull registry.trunner.org/hello-world

Registry Proxy

每次都从远程Registry获取image浪费网络资源，效率低下。虽然我们可以先从远程pull，再push到私有Registry，但这样操作非常烦琐。Registry Proxy可以本地存储image，减少了重复的pull操作。Registry Proxy不支持push。
这次我们使用配置文件运行registry，执行以下命令获取默认配置文件：

$ docker run -it --rm --entrypoint cat registry /etc/docker/registry/config.yml > config.yml

文件内容如下：

version: 0.1
log:
  fields:
    service: registry
storage:
  cache:
    blobdescriptor: inmemory
  filesystem:
    rootdirectory: /var/lib/registry
http:
  addr: :5000
  headers:
    X-Content-Type-Options: [nosniff]
health:
  storagedriver:
    enabled: true
    interval: 10s
    threshold: 3

增加proxy配置：

version: 0.1
log:
  fields:
    service: registry
storage:
  cache:
    blobdescriptor: inmemory
  filesystem:
    rootdirectory: /var/lib/registry
http:
  addr: 0.0.0.0:443
  headers:
    X-Content-Type-Options: [nosniff]
  tls:
    certificate: /var/lib/registry/certs/domain.crt
    key: /var/lib/registry/certs/domain.key
health:
  storagedriver:
    enabled: true
    interval: 10s
    threshold: 3
proxy:
  remoteurl: https://registry-1.docker.io

修改/etc/docker/daemon.json：

{
  "registry-mirrors": ["https://registry.itrunner.org"]
}

重启docker后运行registry：

$ docker run -d --restart always --name registry-proxy -p 443:443 -v /mnt/registry:/var/lib/registry \
registry /var/lib/registry/config.yml

测试：

$ docker pull hello-world

查看proxy：

$ curl -k https://registry.itrunner.org/v2/_catalog
{"repositories":["library/hello-world"]}

可以看到hello-world已保存到proxy中。

搭建Nexus私服

除默认Registry外，使用docker时必须指定Registry域名，能否像Maven一样统一使用一个仓库呢？Nexus 3已支持Docker Repository，同Maven一样分为三种类型：group、hosted、proxy。hosted相当于私有Registry，用来存储公司内部image；proxy为代理Registry；group可以将hosted、proxy、group三者组合在一起。
待续

常见问题

docker error initializing network controller
删除/var/lib/docker/network/files下的文件，重新启动。

参考文档

Docker Documentation
Product Manuals
Docker Glossary
Reference Documentation
Docker Samples
Docker中国
Best practices for writing Dockerfiles
How to Set Up a Registry Proxy Cache with Docker Open Source Registry
Jenkins与Docker的自动化CI/CD实战