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dockerclient来构建的image。
dockerclient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
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--outputaspnetcore.tar.gzhttps://dotnetcli.azureedge.net/dotnet/aspnetcore/Runtime/$ASPNETCORE_VERSION/aspnetcore-runtime-$ASPNETCORE_VERSION-linux-x64.tar.gz&&aspnetcore_sha512='954072376698be69acb7e277df2c243f931e10529def21dcbf9ce277609b30d462126bf8b8b3cab36476bec3d63a927b8e44e59e4d4cade23eef45956fba1ffd'&&echo\"$aspnetcore_sha512aspnetcore.tar.gz\"|sha512sum-c-&&mkdir-p/usr/share/dotnet&&tar-zxfaspnetcore.tar.gz-C/usr/share/dotnet&&rmaspnetcore.tar.gz&&ln-s/usr/share/dotnet/dotnet/usr/bin/dotnet" ], "Image":"sha256:5ecfe4016ac8e911a94aa601a675f7204e9ccab00cbb08e7067c184ad40f34e9", "Volumes":null, "WorkingDir":"", "Entrypoint":null, "OnBuild":null, "Labels":null }, "created":"2019-12-28T08:12:05.676492579Z", "docker_version":"3.0.8", "history":[ { "created":"2019-12-28T04:23:47.4966447Z", "created_by":"/bin/sh-c#(nop)ADDfile:90a2c81769a336bed3f731f44a385f2a65b0916f517a0b77c06c224579bf9a9ain/" }, { "created":"2019-12-28T04:23:47.719507596Z", "created_by":"/bin/sh-c#(nop)CMD[\"bash\"]", "empty_layer":true }, { "created":"2019-12-28T08:11:05.607009582Z", "created_by":"/bin/sh-capt-getupdate&&apt-getinstall-y--no-install-recommendsca-certificateslibc6libgcc1libgssapi-krb5-2libicu57liblttng-ust0libssl1.0.2libstdc++6zlib1g&&rm-rf/var/lib/apt/lists/*" }, { "created":"2019-12-28T08:11:07.64336022Z", "created_by":"/bin/sh-c#(nop)ENVASPNETCORE_URLS=http://+:80DOTNET_RUNNING_IN_CONTAINER=true", "empty_layer":true }, { "created":"2019-12-28T08:11:16.475068844Z", "created_by":"/bin/sh-capt-getupdate&&apt-getinstall-y--no-install-recommendscurl&&rm-rf/var/lib/apt/lists/*" }, { "created":"2019-12-28T08:11:43.814078508Z", "created_by":"/bin/sh-c#(nop)ENVASPNETCORE_VERSION=2.2.8", "empty_layer":true }, { "created":"2019-12-28T08:12:05.676492579Z", "created_by":"/bin/sh-ccurl-SL--outputaspnetcore.tar.gzhttps://dotnetcli.azureedge.net/dotnet/aspnetcore/Runtime/$ASPNETCORE_VERSION/aspnetcore-runtime-$ASPNETCORE_VERSION-linux-x64.tar.gz&&aspnetcore_sha512='954072376698be69acb7e277df2c243f931e10529def21dcbf9ce277609b30d462126bf8b8b3cab36476bec3d63a927b8e44e59e4d4cade23eef45956fba1ffd'&&echo\"$aspnetcore_sha512aspnetcore.tar.gz\"|sha512sum-c-&&mkdir-p/usr/share/dotnet&&tar-zxfaspnetcore.tar.gz-C/usr/share/dotnet&&rmaspnetcore.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.json
config.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
我开源的docker镜像构建,让你不用装docker也能快速构建容器镜像
支持以下镜像仓库作为基础镜像构建
- dockerhub
- aliyun
- 腾讯云
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