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。
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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/2.2Accept: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
GET:https://mcr.microsoft.com/v2/dotnet/core/aspnet/blobs/sha256:e7e3b238011ce0f2b9350153535fe273caa01f0e7188d0b91f965b3802ddc600{ "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" ] }}根据diff_ids里面去下载对应layers
下载完后对比摘要一致，确保镜像文件合法性
路径规则：
https://mcr.microsoft.com/v2/dotnet/core/aspnet/blobs/sha256:XXXXXX
构建我们的镜像在基础镜像的配置基础上加入我们的自定义配置
Entrypoint Cmd Ports Environment ImageWorkingDirectory Volumes Labels在基础镜像的所有的layers把我们要打包到镜像也做成一个layer
生成的镜像tar包解压出来
多了一个 tar.gz文件，解压之后 就是我们打包放进去的文件
原来基础镜像有4个layer 加上我们的 共5个 config.json manifest.jsonconfig.json对比与基础镜像
我们来复习下构建镜像的过程 根据镜像名称拉取mainfest
根据mainfest拉取config 根据config拉取layers 下载各个layer 修改到基础镜像的配置(config.json和mainfest.json) 加入我们要加入的文件layer知道原理后我们可以自己写一个工具来实现整个过程
支持以下镜像仓库作为基础镜像构建
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