Docker鏡像構建原理解析(不裝docker也能構建鏡像)

Posted on 2021-03-03 by WalkonNet

在devops流程裡面構建鏡像是一個非常重要的過程，一般構建鏡像是寫dockerfile文件然後通過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

然後解析你寫的dockerfile構建新的image。

本文帶你瞭解

pull 命令背後是怎麼做的？
build 命令背後是怎麼做的？

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文件裡面都是摘要(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裡面去下載對應layers

下載完後對比摘要一致，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

多瞭一個 tar.gz文件，解壓之後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

知道原理後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

docker hub
aliyun
騰訊雲

到此這篇關於Docker鏡像構建原理解析(不裝docker也能構建鏡像)的文章就介紹到這瞭,更多相關Docker鏡像構建內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！

Docker鏡像構建原理解析(不裝docker也能構建鏡像)

構建我們的鏡像

推薦閱讀：

發佈留言取消回覆

近期文章

構建我們的鏡像

推薦閱讀：

發佈留言 取消回覆

近期文章

標籤

發佈留言取消回覆