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镜像的获取

  1. 从registry拉取
    • public（公有）
    • private（私有）
  2. 从Dockerfile构建（在线）
  3. 文件导入（离线）

Docker Image Registry

类似于Ubuntu的apt-get源，Go的proxy，git的GitHub，用于指定从哪里摘取镜像，默认是Docker Hub，也就是https://hub.docker.com/。

配置registry可参考：镜像加速器 - Docker — 从入门到实践。

镜像的基本操作

$ docker image

Usage:  docker image COMMAND

Manage images

Commands:
build       Build an image from a Dockerfile
history     Show the history of an image
import      Import the contents from a tarball to create a filesystem image
inspect     Display detailed information on one or more images
load        Load an image from a tar archive or STDIN
ls          List images
prune       Remove unused images
pull        Pull an image or a repository from a registry
push        Push an image or a repository to a registry
rm          Remove one or more images
save        Save one or more images to a tar archive (streamed to STDOUT by default)
tag         Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE

Run 'docker image COMMAND --help' for more information on a command.

镜像的拉取

默认从Docker Hub拉取，如果不指定版本，会拉取最新版。

$ docker pull nginx
Using default tag: latest
latest: Pulling from library/nginx
69692152171a: Pull complete
49f7d34d62c1: Pull complete
5f97dc5d71ab: Pull complete
cfcd0711b93a: Pull complete
be6172d7651b: Pull complete
de9813870342: Pull complete
Digest: sha256:df13abe416e37eb3db4722840dd479b00ba193ac6606e7902331dcea50f4f1f2
Status: Downloaded newer image for nginx:latest
docker.io/library/nginx:latest

指定版本：

$ docker pull nginx:1.20.0
1.20.0: Pulling from library/nginx
69692152171a: Already exists
965615a5cec8: Pull complete
b141b026b9ce: Pull complete
8d70dc384fb3: Pull complete
525e372d6dee: Pull complete
Digest: sha256:ea4560b87ff03479670d15df426f7d02e30cb6340dcd3004cdfc048d6a1d54b4
Status: Downloaded newer image for nginx:1.20.0
docker.io/library/nginx:1.20.0

从Quay上拉取镜像：

$ docker pull quay.io/bitnami/nginx
Using default tag: latest
latest: Pulling from bitnami/nginx
2e6370f1e2d3: Pull complete
2d464c695e97: Pull complete
83eb3b1671f4: Pull complete
364c139450f9: Pull complete
dc453d5ae92e: Pull complete
09bd59934b83: Pull complete
8d2bd62eedfb: Pull complete
8ac060ae1ede: Pull complete
c7c9bc2f4f9d: Pull complete
6dd7098b85fa: Pull complete
894a70299d18: Pull complete
Digest: sha256:d143befa04e503472603190da62db157383797d281fb04e6a72c85b48e0b3239
Status: Downloaded newer image for quay.io/bitnami/nginx:latest
quay.io/bitnami/nginx:latest

镜像的查看

$ docker image ls
REPOSITORY              TAG       IMAGE ID       CREATED       SIZE
quay.io/bitnami/nginx   latest    0922eabe1625   6 hours ago   89.3MB
nginx                   1.20.0    7ab27dbbfbdf   10 days ago   133MB
nginx                   latest    f0b8a9a54136   10 days ago   133MB

docker image inspect <image ID>可以查看一个镜像的详细信息。

镜像的删除

$ docker image rm 0922eabe1625
Untagged: quay.io/bitnami/nginx:latest
Untagged: quay.io/bitnami/nginx@sha256:d143befa04e503472603190da62db157383797d281fb04e6a72c85b48e0b3239
Deleted: sha256:0922eabe16250e2f4711146e31b7aac0e547f52daa6cf01c9d00cf64d49c68c8
Deleted: sha256:5eee4ed0f6b242e2c6e4f4066c7aca26bf9b3b021b511b56a0dadd52610606bd
Deleted: sha256:472a75325eda417558f9100ff8b4a97f4a5e8586a14eb9c8fc12f944b26a21f8
Deleted: sha256:cdcb5872f8a64a0b5839711fcd2a87ba05795e5bf6a70ba9510b8066cdd25e76
Deleted: sha256:e0f1b7345a521469bbeb7ec53ef98227bd38c87efa19855c5ba0db0ac25c8e83
Deleted: sha256:11b9c2261cfc687fba8d300b83434854cc01e91a2f8b1c21dadd937e59290c99
Deleted: sha256:4819311ec2867ad82d017253500be1148fc335ad13b6c1eb6875154da582fcf2
Deleted: sha256:784480add553b8e8d5ee1bbd229ed8be92099e5fb61009ed7398b93d5705a560
Deleted: sha256:e0c520d1a43832d5d2b1028e3f57047f9d9f71078c0187f4bb05e6a6a572993d
Deleted: sha256:94d5b1d6c9e31de42ce58b8ce51eb6fb5292ec889a6d95763ad2905330b92762
Deleted: sha256:95deba55c490bbb8de44551d3e6a89704758c93ba8503a593cb7c07dfbae0058
Deleted: sha256:1ad1d903ef1def850cd44e2010b46542196e5f91e53317dbdb2c1eedfc2d770c

如果通过镜像创建了容器，则必须先删除容器，然后才能删除镜像。

镜像的导入和导出

参考docker image --help，要用到的命令是save和load。

docker image save nginx:1.20.0 -o nginx.image
docker image load -i nginx.image

Dockerfile介绍

Docker can build images automatically by reading the instructions from a Dockerfile. A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using docker build users can create an automated build that executes several command-line instructions in succession.

参考：https://docs.docker.com/engine/reference/builder/

  • Dockerfile是用于构建docker镜像的文件
  • Dockerfile里包含了构建镜像所需的“指令”
  • Dockerfile有其特定的语法规则

Dockerfile示例：执行Python程序

假设我们要在一台ubuntu 21.04上运行下面这个hello.py的Python程序。

hello.py
print("hello docker")

第一步，准备Python环境：

apt-get update && \
DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y python3.9 python3-pip python3.9-dev

第二步，运行hello.py：

$ python3 hello.py
hello docker


以上步骤对应的Dockerfile为：

Dockerfile
FROM ubuntu:21.04
RUN apt-get update && \
    DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y python3.9 python3-pip python3.9-dev
ADD hello.py /
CMD ["python3", "/hello.py"]

关于Dockerfile的语法可以参考：https://docs.docker.com/engine/reference/builder/

镜像的构建和分享

在当前目录下准备下面两个文件：

hello.py
print("hello docker")
Dockerfile
FROM ubuntu:21.04
RUN apt-get update && \
    DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y python3.9 python3-pip python3.9-dev
ADD hello.py /
CMD ["python3", "/hello.py"]

执行以下命令进行Dockerfile的构建：

docker build -t hello .

命令参数可参考docker build --help，-t用于指定镜像的名称和版本，比如hello:1.0.0，不指定版本时默认为latest，.用于指定Dockerfile的路径。

接下来就是创建容器并运行：

docker container run --it hello


接下来是将创建好的镜像推送到Docker Hub，实现镜像的分享功能。

首先需要注册Docker Hub的账号，然后在命令行通过docker login登录账号。接下来是构建符合Docker Hub命名风格的镜像，比如：

docker build -t luqiang2014/hello:v1.0 .

或是将已经构建好的镜像重新打tag，比如：

docker image tag hello luqiang2014/hello:v1.0

接下来就是通过docker image push实现镜像的推送：

dock image push luqiang2014/hello:v1.0

推送完成后可以在Docker Hub的个人仓库界面查看仓库。还可以使用docker pull来拉取自己的仓库，如下：

docker image pull luqiang2014/hello:v1.0


通过 commit 创建镜像


关于 scratch 镜像

Scratch是一个空的Docker镜像。

通过scratch来构建一个基础镜像。

hello.c
#include <stdio.h>
int main()
{
    printf("hello docker\n");
}

编译成一个二进制文件

$ gcc --static -o hello hello.c
$ ./hello
hello docker
$
Dockerfile
FROM scratch
ADD hello /
CMD ["/hello"]

构建

$ docker build -t hello .
$ docker image ls
REPOSITORY   TAG       IMAGE ID       CREATED          SIZE
hello        latest    2936e77a9daa   40 minutes ago   872kB

运行

$ docker container run -it hello
hello docker






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