不装docker也能构建镜像 Docker镜像构建原理解析

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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：
【不装docker也能构建镜像 Docker镜像构建原理解析】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

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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

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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 \"$aspnetcore_sha512 aspnetcore.tar.gz\" | sha512sum -c -&& mkdir -p /usr/share/dotnet&& tar -zxf aspnetcore.tar.gz -C /usr/share/dotnet&& rm aspnetcore.tar.gz&& ln -s /usr/share/dotnet/dotnet /usr/bin/dotnet"],"Image": "sha256:5ecfe4016ac8e911a94aa601a675f7204e9ccab00cbb08e7067c184ad40f34e9","Volumes": null,"WorkingDir": "","Entrypoint": null,"OnBuild": null,"Labels": null},"created": "2019-12-28T08:12:05.676492579Z","docker_version": "3.0.8","history": [{"created": "2019-12-28T04:23:47.4966447Z","created_by": "/bin/sh -c #(nop) ADD file:90a2c81769a336bed3f731f44a385f2a65b0916f517a0b77c06c224579bf9a9a in / "},{"created": "2019-12-28T04:23:47.719507596Z","created_by": "/bin/sh -c #(nop) CMD [\"bash\"]","empty_layer": true},{"created": "2019-12-28T08:11:05.607009582Z","created_by": "/bin/sh -c apt-get update&& apt-get install -y --no-install-recommendsca-certificateslibc6libgcc1libgssapi-krb5-2libicu57liblttng-ust0libssl1.0.2libstdc++6zlib1g&& rm -rf /var/lib/apt/lists/*"},{"created": "2019-12-28T08:11:07.64336022Z","created_by": "/bin/sh -c #(nop) ENV ASPNETCORE_URLS=http://+:80 DOTNET_RUNNING_IN_CONTAINER=true","empty_layer": true},{"created": "2019-12-28T08:11:16.475068844Z","created_by": "/bin/sh -c apt-get update&& apt-get install -y --no-install-recommendscurl&& rm -rf /var/lib/apt/lists/*"},{"created": "2019-12-28T08:11:43.814078508Z","created_by": "/bin/sh -c #(nop) ENV ASPNETCORE_VERSION=2.2.8","empty_layer": true},{"created": "2019-12-28T08:12:05.676492579Z","created_by": "/bin/sh -c curl -SL --output aspnetcore.tar.gz https://dotnetcli.azureedge.net/dotnet/aspnetcore/Runtime/$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