Docker镜像构建原理解析(不装docker也能构建镜像)

在devops流程里面构建镜像是一个非常重要的过程，一般构建镜像是写dockerfile文件然后通过docker client来构建的image。

docker client 会先检查本地有没有image，如果没有帮你从镜像仓库 pull 下来

然后解析你写的dockerfile构建新的image。

本文带你了解

pull 命令背后是怎么做的？
build 命令背后是怎么做的？

下篇文章带你解析：

如果我不用docker 我如何构建一个镜像？

我们以微软的aspnet2.2为基础构建一个aspnetcore项目的镜像为例子

mcr.microsoft.com/dotnet/core/aspnet:2.2

根据基础镜像REGISTRY去获取mainfest信息

https://mcr.microsoft.com/v2/dotnet/core/aspnet/manifests/2.2

Accept:

application/vnd.oci.image.manifest.v1+json,application/vnd.docker.distribution.manifest.v2+json,application/vnd.docker.distribution.manifest.v1+json

获取到的内容如下：

{

"schemaVersion": 2,

"mediaType": "application/vnd.docker.distribution.manifest.v2+json",

"config": {

"mediaType": "application/vnd.docker.container.image.v1+json",

"size": 4039,

"digest": "sha256:e7e3b238011ce0f2b9350153535fe273caa01f0e7188d0b91f965b3802ddc600"

},

"layers": [

{

"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",

"size": 22524609,

"digest": "sha256:804555ee037604c40de144f9f8da0d826d38db82f15d74cded32790fe279a8f6"

},

{

"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",

"size": 17692725,

"digest": "sha256:970251047358aea56ba6db6975b14ff12470b75de0c2477f4445240ddd727fd4"

},

{

"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",

"size": 2978257,

"digest": "sha256:f3d4c41a4fd13f35c0b46f19a4e27845f4695163cc7174d908ff84836bbc2f5a"

},

{

"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",

"size": 62145592,

"digest": "sha256:bd391c46585f9f8d84992bbaa9087189148c1601968eaaf097d5b3ed60840e5e"

}

]

}

mainfest文件里面都是摘要(digest)记录

config信息摘要
每个layer的摘要（上面的例子有4个）

根据上面的config信息摘要获取config详情

1	`GET:https://mcr.microsoft.com/v2/dotnet/core/aspnet/blobs/sha256:e7e3b238011ce0f2b9350153535fe273caa01f0e7188d0b91f965b3802ddc600`

100

101

102

103

104

{

"architecture": "amd64",

"config": {

"Hostname": "",

"Domainname": "",

"User": "",

"AttachStdin": false,

"AttachStdout": false,

"AttachStderr": false,

"Tty": false,

"OpenStdin": false,

"StdinOnce": false,

"Env": [

"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",

"ASPNETCORE_URLS=http://+:80",

"DOTNET_RUNNING_IN_CONTAINER=true",

"ASPNETCORE_VERSION=2.2.8"

],

"Cmd": [

"bash"

],

"ArgsEscaped": true,

"Image": "sha256:5ecfe4016ac8e911a94aa601a675f7204e9ccab00cbb08e7067c184ad40f34e9",

"Volumes": null,

"WorkingDir": "",

"Entrypoint": null,

"OnBuild": null,

"Labels": null

},

"container": "14196c2f9c327d41e26682d32c7c89c4e7c78aa32f8b7501a23192035a9f4844",

"container_config": {

"Hostname": "",

"Domainname": "",

"User": "",

"AttachStdin": false,

"AttachStdout": false,

"AttachStderr": false,

"Tty": false,

"OpenStdin": false,

"StdinOnce": false,

"Env": [

"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",

"ASPNETCORE_URLS=http://+:80",

"DOTNET_RUNNING_IN_CONTAINER=true",

"ASPNETCORE_VERSION=2.2.8"

],

"Cmd": [

"/bin/sh",

"-c",

"curl -SL --output aspnetcore.tar.gz https://dotnetcli.azureedge.net/dotnet/aspnetcore/Runtime/$ASPNETCORE_VERSION/aspnetcore-runtime-$ASPNETCORE_VERSION-linux-x64.tar.gz && aspnetcore_sha512='954072376698be69acb7e277df2c243f931e10529def21dcbf9ce277609b30d462126bf8b8b3cab36476bec3d63a927b8e44e59e4d4cade23eef45956fba1ffd' && echo \\"$aspnetcore_sha512 aspnetcore.tar.gz\\" | sha512sum -c - && mkdir -p /usr/share/dotnet && tar -zxf aspnetcore.tar.gz -C /usr/share/dotnet && rm aspnetcore.tar.gz && ln -s /usr/share/dotnet/dotnet /usr/bin/dotnet"

],

"Image": "sha256:5ecfe4016ac8e911a94aa601a675f7204e9ccab00cbb08e7067c184ad40f34e9",

"Volumes": null,

"WorkingDir": "",

"Entrypoint": null,

"OnBuild": null,

"Labels": null

},

"created": "2019-12-28T08:12:05.676492579Z",

"docker_version": "3.0.8",

"history": [

{

"created": "2019-12-28T04:23:47.4966447Z",

"created_by": "/bin/sh -c #(nop) ADD file:90a2c81769a336bed3f731f44a385f2a65b0916f517a0b77c06c224579bf9a9a in / "

},

{

"created": "2019-12-28T04:23:47.719507596Z",

"created_by": "/bin/sh -c #(nop) CMD [\\"bash\\"]",

"empty_layer": true

},

{

"created": "2019-12-28T08:11:05.607009582Z",

"created_by": "/bin/sh -c apt-get update && apt-get install -y --no-install-recommends ca-certificates libc6 libgcc1 libgssapi-krb5-2 libicu57 liblttng-ust0 libssl1.0.2 libstdc++6 zlib1g && rm -rf /var/lib/apt/lists/*"

},

{

"created": "2019-12-28T08:11:07.64336022Z",

"created_by": "/bin/sh -c #(nop) ENV ASPNETCORE_URLS=http://+:80 DOTNET_RUNNING_IN_CONTAINER=true",

"empty_layer": true

},

{

"created": "2019-12-28T08:11:16.475068844Z",

"created_by": "/bin/sh -c apt-get update && apt-get install -y --no-install-recommends curl && rm -rf /var/lib/apt/lists/*"

},

{

"created": "2019-12-28T08:11:43.814078508Z",

"created_by": "/bin/sh -c #(nop) ENV ASPNETCORE_VERSION=2.2.8",

"empty_layer": true

},

{

"created": "2019-12-28T08:12:05.676492579Z",

"created_by": "/bin/sh -c curl -SL --output aspnetcore.tar.gz https://dotnetcli.azureedge.net/dotnet/aspnetcore/Runtime/$ASPNETCORE_VERSION/aspnetcore-runtime-$ASPNETCORE_VERSION-linux-x64.tar.gz && aspnetcore_sha512='954072376698be69acb7e277df2c243f931e10529def21dcbf9ce277609b30d462126bf8b8b3cab36476bec3d63a927b8e44e59e4d4cade23eef45956fba1ffd' && echo \\"$aspnetcore_sha512 aspnetcore.tar.gz\\" | sha512sum -c - && mkdir -p /usr/share/dotnet && tar -zxf aspnetcore.tar.gz -C /usr/share/dotnet && rm aspnetcore.tar.gz && ln -s /usr/share/dotnet/dotnet /usr/bin/dotnet"

}

],

"os": "linux",

"rootfs": {

"type": "layers",

"diff_ids": [

"sha256:814c70fdae62bc26c603bfae861f00fb1c77fc0b1ee8d565717846f4df24ae5d",

"sha256:0cf75cb98eb2e0a82631d4aff71b40ba79ff7f83e0361f696875e592a1a4cefc",

"sha256:15e45d99c92686fb1fd61a41431d8400d7a0e8381595d09d666b0809c4f5d993",

"sha256:579a8f1d6a123f98095c0b1a1395079f7504391fd2a8bc529dede305a2072a36"

]

}