在devops流程里面 構建鏡像是一個非常重要的過程，一般構建鏡像是寫dockerfile文件然后通過docker client來構建的image。
docker client 會先檢查本地有沒有image，如果沒有幫你 從鏡像倉庫 pull 下來
然后解析你寫的dockerfile構建新的image。
本文帶你了解
- pull 命令 背后是怎么做的？
- build 命令 背后是怎么做的？
下篇文章帶你解析：
如果我不用docker 我如何構建一個鏡像？
我們以微軟的aspnet2.2為基礎構建一個aspnetcore項目的鏡像為例子
mcr.microsoft.com/dotnet/core/aspnet:2.2
根據基礎鏡像REGISTRY去獲取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
獲取到的內容如下：
{
"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)記錄
- config信息摘要
- 每個layer的摘要 （上面的例子有4個）
根據上面的config信息摘要獲取config詳情
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"
]
}
}
根據diff_ids里面去下載對應layers
下載完后對比摘要一致，確保鏡像文件合法性
路徑規則：
https://mcr.microsoft.com/v2/dotnet/core/aspnet/blobs/sha256:XXXXXX
構建我們的鏡像
在基礎鏡像的配置基礎上加入我們的自定義配置
- Entrypoint
- Cmd
- Ports
- Environment
- ImageWorkingDirectory
- Volumes
- Labels
在基礎鏡像的所有的layers把我們要打包到鏡像也做成一個layer
生成的鏡像tar包解壓出來
多了一個 tar.gz文件，解壓之后 就是我們打包放進去的文件
- 原來基礎鏡像有4個layer 加上我們的 共5個
- config.json
- manifest.json
config.json對比與基礎鏡像
我們來復習下構建鏡像的過程 根據鏡像名稱拉取mainfest
- 根據mainfest拉取config
- 根據config拉取layers
- 下載各個layer
- 修改到基礎鏡像的配置(config.json和mainfest.json)
- 加入我們要加入的文件layer
知道原理后我們可以自己寫一個工具來實現整個過程
我開源的docker鏡像構建，讓你不用裝docker也能快速構建容器鏡像
支持以下鏡像倉庫作為基礎鏡像構建
到此這篇關于Docker鏡像構建原理解析(不裝docker也能構建鏡像)的文章就介紹到這了,更多相關Docker鏡像構建內容請搜索腳本之家以前的文章或繼續瀏覽下面的相關文章希望大家以后多多支持腳本之家！
