构建多架构镜像的最佳实践

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在云时代，容器化已经成为一种事实，把软件产品打包、构建成 Docker 镜像是最基本、最关键的一步。在信创的大背景下，云环境中会存在 x86、arm 等不同的架构，所以在构建镜像时需要构建出多种架构的镜像，以适配不同架构的服务器。

在拉取 Docker 镜像时，会根据当前环境的架构自动拉取对应架构的镜像，如：在 x86 环境下拉取的镜像为 x86 架构的镜像，在 arm 环境下拉取的镜像为 arm 架构的镜像。（前提是，该镜像是多架构的镜像）

本文将针对基于 Docker Buildx 来构建多架构的镜像展开说明（一次构建多架构的镜像）。

1、buildx 安装

Docker Buildx 是一个 CLI 插件，它扩展了 Docker 命令，完全支持 Moby BuildKit 构建器工具包提供的功能。它提供与 docker build 相同的用户体验，具有许多新功能，例如创建作用域构建器实例和同时针对多个节点进行构建。

1. 下载 buildx 二进制文件。
在 Github Release 页面(https://github.com/docker/buildx/releases/latest)下载最新的 buildx 二进制文件。
根据您的操作系统选择对应的二进制文件。
2. buildx 复制到 Docker 对应目录。
重命名下载的 buildx 二进制文件，并将其复制到您操作系统对应的目录：
操作系统二进制名称目标文件夹
Linux docker-buildx $HOME/.docker/cli-plugins
MacOS docker-buildx $HOME/.docker/cli-plugins
Windows docker-buildx.exe %USERPROFILE%\.docker\cli-plugins
例如，我的 MacOS：
```
xcbeyond@xcbeyonddeMacBook-Pro ~ % mv ~/Downloads/buildx-v0.7.1.darwin-arm64 ~/.docker/cli-plugins/docker-buildx
xcbeyond@xcbeyonddeMacBook-Pro ~ % chmod +x ~/.docker/cli-plugins/docker-buildx
```
注意：需对 buildx 二进制文件赋予权限，执行 chmod +x。

操作系统	二进制名称	目标文件夹
Linux	docker-buildx	`$HOME/.docker/cli-plugins`
MacOS	docker-buildx	`$HOME/.docker/cli-plugins`
Windows	docker-buildx.exe	`%USERPROFILE%\.docker\cli-plugins`

3. 检查 buildx。

执行 docker buildx version：

xcbeyond@xcbeyonddeMacBook-Pro ~ % docker buildx version
github.com/docker/buildx v0.7.1 05846896d149da05f3d6fd1e7770da187b52a247

2、开启 binfmt_misc 来运行非本地架构的 Docker 镜像

如果您使用的是 Mac 或者 Windows 版本 Docker 桌面版，则可以跳过这个步骤，因为 binfmt_misc 默认开启。

如果使用的是其它平台，可使用 tonistiigi/binfmt 镜像进行安装：

 docker run --privileged --rm tonistiigi/binfmt --install all

3、将默认 Docker 构建器切换为多架构构建器

默认情况下，Docker 会使用默认构建器，是不支持多架构构建。

为了构建多架构的镜像，需要创建新的支持多架构的构建器，需执行 docker buildx create --use：

xcbeyond@xcbeyonddeMacBook-Pro % docker buildx create --use --name mybuilder
mybuilder

查看新的多架构构建器是否生效，需执行 docker buildx ls：

xcbeyond@xcbeyonddeMacBook-Pro % docker buildx ls
NAME/NODE       DRIVER/ENDPOINT             STATUS   PLATFORMS
mybuilder *     docker-container                     
  mybuilder0    unix:///var/run/docker.sock inactive 
desktop-linux   docker                               
  desktop-linux desktop-linux               running  linux/arm64, linux/amd64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/arm/v7, linux/arm/v6
default         docker                               
  default       default                     running  linux/arm64, linux/amd64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/arm/v7, linux/arm/v6

4、构建多架构镜像

1. 编写测试程序。

为方便测试，用 Golang 写了一个简单的程序，并输出当前程序运行环境的架构信息：

package main

import (
   "fmt"
   "runtime"
)

func main() {
   fmt.Printf("the current platform architecture is %s.\n", runtime.GOARCH)
}

2. 编写 Dockerfile。

编写该程序的 Dockerfile(https://xcbeyond.cn/blog/containers/build-multi-platform-images-best-practices/Dockerfile)：

FROM xcbeyond/go-builder:1.16
LABEL maintainer xcbeyond
WORKDIR /app
COPY multi-arch-test.go /appRUN go build -o multi-arch-test /app/multi-arch-test.go
CMD ["./multi-arch-test"]

3. 构建多架构镜像。

通过命令 docker buildx build -t <image-name> --platform=linux/arm64,linux/amd64 . --push，构建一个支持 arm64 和 amd64 架构的多架构镜像，并推送至 Docker Hub：

（参数 --push 会自动将镜像推送到 Docker Hub，本地并不会保留该镜像。如果不想推送，则可去掉该参数。）

xcbeyond@xcbeyonddeMacBook-Pro build-multi-platform-images-best-practices % docker buildx build -t xcbeyond/multi-arch-test --platform=linux/arm64,linux/amd64 . --push
[+] Building 3105.4s (19/19) FINISHED                                                                                                                                                                       
=> [internal] load build definition from Dockerfile                                                                                                                                                   0.0s
=> => transferring dockerfile: 222B                                                                                                                                                                   0.0s
=> [internal] load .dockerignore                                                                                                                                                                      0.0s
=> => transferring context: 2B                                                                                                                                                                        0.0s
=> [linux/amd64 internal] load metadata for docker.io/xcbeyond/go-builder:1.16                                                                                                                        5.2s
=> [linux/arm64 internal] load metadata for docker.io/xcbeyond/go-builder:1.16                                                                                                                        4.9s
=> [auth] xcbeyond/go-builder:pull token for registry-1.docker.io                                                                                                                                     0.0s
=> [internal] load build context                                                                                                                                                                      0.0s
=> => transferring context: 40B                                                                                                                                                                       0.0s
=> [linux/amd64 1/4] FROM docker.io/xcbeyond/go-builder:1.16@sha256:ace56967e44e98b1a8c286ad97717c878650d0312ac3e69767234f766601d6fc                                                               2323.9s
=> => resolve docker.io/xcbeyond/go-builder:1.16@sha256:ace56967e44e98b1a8c286ad97717c878650d0312ac3e69767234f766601d6fc                                                                              0.0s
=> => sha256:6e1d20a8313edd44a36cb9198f4d11ac5eedb41d1faf5e8a33c5a0a5a25d2b92 85.80MB / 85.80MB                                                                                                    2318.7s
=> => sha256:6494e4811622b31c027ccac322ca463937fd805f569a93e6f15c01aade718793 54.57MB / 54.57MB                                                                                                      27.3s
=> => sha256:5b59121a0c3517cfd68aba8a3955cbb40ca12dd56db3317e3a17cf56131ca915 129.08MB / 129.08MB                                                                                                    77.1s
=> => sha256:cb5b7ae361722f070eca53f35823ed21baa85d61d5d95cd5a95ab53d740cdd56 10.87MB / 10.87MB                                                                                                      96.5s
=> => sha256:9b829c73b52b92b97d5c07a54fb0f3e921995a296c714b53a32ae67d19231fcd 5.15MB / 5.15MB                                                                                                         5.2s
=> => sha256:0e29546d541cdbd309281d21a73a9d1db78665c1b95b74f32b009e0b77a6e1e3 54.92MB / 54.92MB                                                                                                      61.0s
=> => extracting sha256:0e29546d541cdbd309281d21a73a9d1db78665c1b95b74f32b009e0b77a6e1e3                                                                                                              1.5s
=> => extracting sha256:9b829c73b52b92b97d5c07a54fb0f3e921995a296c714b53a32ae67d19231fcd                                                                                                              0.1s
=> => extracting sha256:cb5b7ae361722f070eca53f35823ed21baa85d61d5d95cd5a95ab53d740cdd56                                                                                                              0.3s
=> => extracting sha256:6494e4811622b31c027ccac322ca463937fd805f569a93e6f15c01aade718793                                                                                                              1.6s
=> => extracting sha256:6e1d20a8313edd44a36cb9198f4d11ac5eedb41d1faf5e8a33c5a0a5a25d2b92                                                                                                              1.9s
=> => extracting sha256:5b59121a0c3517cfd68aba8a3955cbb40ca12dd56db3317e3a17cf56131ca915                                                                                                              3.3s
=> => extracting sha256:2db41f0db9d9d9a1f49978ec31e8d187f491767e9b377f5ee121827c407e015e                                                                                                              0.0s
=> [linux/arm64 1/4] FROM docker.io/xcbeyond/go-builder:1.16@sha256:ace56967e44e98b1a8c286ad97717c878650d0312ac3e69767234f766601d6fc                                                               2187.3s
=> => resolve docker.io/xcbeyond/go-builder:1.16@sha256:ace56967e44e98b1a8c286ad97717c878650d0312ac3e69767234f766601d6fc                                                                              0.0s
=> => sha256:221ff675cd357b3b345da24f781791fc9b91066d687f9e928993aab31618d13d 99.63MB / 99.63MB                                                                                                      54.3s
=> => sha256:627b3401fb617535edd16e96bd5941ecea7fe10ce6087bd47707602cfc396c2b 81.01MB / 81.01MB                                                                                                     472.1s
=> => sha256:841dd868500b6685b6cda93c97ea76e817b427d7a10bf73e9d03356fac199ffd 54.67MB / 54.67MB                                                                                                    2084.9s
=> => sha256:aa9c5b49b9db3dd2553e8ae6c2081b77274ec0a8b1f9903b0e5ac83900642098 10.66MB / 10.66MB                                                                                                       6.2s
=> => sha256:ac9d381bd1e98fa8759f80ff42db63c8fce4ac9407b2e7c8e0f031ed9f96432b 5.14MB / 5.14MB                                                                                                         6.8s
=> => sha256:94a23d3cb5be24659b25f17537307e7f568d665244f6a383c1c6e51e31080749 53.60MB / 53.60MB                                                                                                      22.7s
=> => extracting sha256:94a23d3cb5be24659b25f17537307e7f568d665244f6a383c1c6e51e31080749                                                                                                              1.5s
=> => extracting sha256:ac9d381bd1e98fa8759f80ff42db63c8fce4ac9407b2e7c8e0f031ed9f96432b                                                                                                              0.1s
=> => extracting sha256:aa9c5b49b9db3dd2553e8ae6c2081b77274ec0a8b1f9903b0e5ac83900642098                                                                                                              0.2s
=> => extracting sha256:841dd868500b6685b6cda93c97ea76e817b427d7a10bf73e9d03356fac199ffd                                                                                                              1.5s
=> => extracting sha256:627b3401fb617535edd16e96bd5941ecea7fe10ce6087bd47707602cfc396c2b                                                                                                              1.7s
=> => extracting sha256:221ff675cd357b3b345da24f781791fc9b91066d687f9e928993aab31618d13d                                                                                                              2.7s
=> => extracting sha256:10c716f05a00666c190fb40f99503dc83b2886de744ab9b3dc6c5d37d01f6e49                                                                                                              0.0s
=> [auth] xcbeyond/go-builder:pull token for registry-1.docker.io                                                                                                                                     0.0s
=> [linux/arm64 2/4] WORKDIR /app                                                                                                                                                                     0.1s
=> [linux/arm64 3/4] COPY multi-arch-test.go /app                                                                                                                                                     0.0s
=> [linux/arm64 4/4] RUN go build -o multi-arch-test /app/multi-arch-test.go                                                                                                                          0.3s
=> [linux/amd64 2/4] WORKDIR /app                                                                                                                                                                     0.2s
=> [linux/amd64 3/4] COPY multi-arch-test.go /app                                                                                                                                                     0.0s
=> [linux/amd64 4/4] RUN go build -o multi-arch-test /app/multi-arch-test.go                                                                                                                          1.5s
=> exporting to image                                                                                                                                                                               774.4s
=> => exporting layers                                                                                                                                                                               10.5s
=> => exporting manifest sha256:f38420339c9665b4f7d8b1e5edc66dc09e596ec7aa78113914b8a5b1b900e9e2                                                                                                      0.0s
=> => exporting config sha256:628f504898973d1d935ffd37993d1db5fdc4715c5d58467db2c6531d3d7d3181                                                                                                        0.0s
=> => exporting manifest sha256:a259302dca0d3f432d08f578e3243c5244bc50e54ea561c80dba03622897fcfd                                                                                                      0.0s
=> => exporting config sha256:47e7af533f821be5ba256919303e0de3b39990109a419a98dbfddc6c82086822                                                                                                        0.0s
=> => exporting manifest list sha256:8417543ebc47e6040a67a392d6ee9de05735ed464e48b22fcc3bdf66ce22224b                                                                                                 0.0s
=> => pushing layers                                                                                                                                                                                761.8s
=> => pushing manifest for docker.io/xcbeyond/multi-arch-test:latest@sha256:8417543ebc47e6040a67a392d6ee9de05735ed464e48b22fcc3bdf66ce22224b                                                          2.0s
=> [auth] xcbeyond/multi-arch-test:pull,push token for registry-1.docker.io                                                                                                                           0.0s
=> [auth] xcbeyond/multi-arch-test:pull,push token for registry-1.docker.io                                                                                                                           0.0s
=> [auth] xcbeyond/multi-arch-test:pull,push token for registry-1.docker.io                                                                                                                           0.0s

5、测试多架构镜像

将构建的多架构镜像 xcbeyond/multi-arch-test:latest 进行测试，以确保能够正常运行，并使用对应架构镜像能够输出匹配的架构信息。

1. 查看每个架构镜像的信息。

执行命令 docker manifest inspect，可查看该镜像清单，并能得知该镜像对应架构的镜像 SHA 值：

xcbeyond@xcbeyonddeMacBook-Pro build-multi-platform-images-best-practices % docker manifest inspect xcbeyond/multi-arch-test:latest
{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
   "manifests": [
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 2419,
         "digest": "sha256:f38420339c9665b4f7d8b1e5edc66dc09e596ec7aa78113914b8a5b1b900e9e2",
         "platform": {
            "architecture": "arm64",
            "os": "linux"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 2420,
         "digest": "sha256:a259302dca0d3f432d08f578e3243c5244bc50e54ea561c80dba03622897fcfd",
         "platform": {
            "architecture": "amd64",
            "os": "linux"
         }
      }
   ]
}

也可以直接在 Docker Hub 上直接看到该镜像支持的多架构信息：

2. 根据不同架构镜像的 SHA 值，来逐一运行该镜像，并查看其输出结果。

分别执行 docker run --rm 命令：

arm 架构的镜像：

xcbeyond@xcbeyonddeMacBook-Pro build-multi-platform-images-best-practices % docker run --rm xcbeyond/multi-arch-test:latest@sha256:f38420339c9665b4f7d8b1e5edc66dc09e596ec7aa78113914b8a5b1b900e9e2
Unable to find image 'xcbeyond/multi-arch-test:latest@sha256:f38420339c9665b4f7d8b1e5edc66dc09e596ec7aa78113914b8a5b1b900e9e2' locally
docker.io/xcbeyond/multi-arch-test@sha256:f38420339c9665b4f7d8b1e5edc66dc09e596ec7aa78113914b8a5b1b900e9e2: Pulling from xcbeyond/multi-arch-test
94a23d3cb5be: Pull complete 
ac9d381bd1e9: Pull complete 
aa9c5b49b9db: Pull complete 
841dd868500b: Pull complete 
627b3401fb61: Pull complete 
221ff675cd35: Pull complete 
10c716f05a00: Pull complete 
15bae122089f: Pull complete 
d764b5be0a55: Pull complete 
34bfa57028a2: Pull complete 
Digest: sha256:f38420339c9665b4f7d8b1e5edc66dc09e596ec7aa78113914b8a5b1b900e9e2
Status: Downloaded newer image for xcbeyond/multi-arch-test@sha256:f38420339c9665b4f7d8b1e5edc66dc09e596ec7aa78113914b8a5b1b900e9e2
the current platform architecture is arm64.

x86 架构的镜像：

xcbeyond@xcbeyonddeMacBook-Pro build-multi-platform-images-best-practices % docker run --rm xcbeyond/multi-arch-test:latest@sha256:a259302dca0d3f432d08f578e3243c5244bc50e54ea561c80dba03622897fcfd
Unable to find image 'xcbeyond/multi-arch-test:latest@sha256:a259302dca0d3f432d08f578e3243c5244bc50e54ea561c80dba03622897fcfd' locally
docker.io/xcbeyond/multi-arch-test@sha256:a259302dca0d3f432d08f578e3243c5244bc50e54ea561c80dba03622897fcfd: Pulling from xcbeyond/multi-arch-test
0e29546d541c: Pull complete 
9b829c73b52b: Pull complete 
cb5b7ae36172: Pull complete 
6494e4811622: Pull complete 
6e1d20a8313e: Pull complete 
5b59121a0c35: Pull complete 
2db41f0db9d9: Pull complete 
f708bf6a9dc8: Pull complete 
cb0d69b97354: Pull complete 
a8f5aa83ecfb: Pull complete 
Digest: sha256:a259302dca0d3f432d08f578e3243c5244bc50e54ea561c80dba03622897fcfd
Status: Downloaded newer image for xcbeyond/multi-arch-test@sha256:a259302dca0d3f432d08f578e3243c5244bc50e54ea561c80dba03622897fcfd
the current platform architecture is amd64.

上面的输出结果，和我们的期望一致：多架构的镜像构建成功，并能在各自架构环境下运行。

6、总结

多架构镜像是基于 Docker Buildx 构建的，目前 buildx 还需额外安装，未来 buildx 很可能成为 docker build 命令的一部分，无需额外安装，毕竟多架构镜像已在各种场景中应用广泛起来了。

参考文章：

https://docs.docker.com/buildx/working-with-buildx/
https://www.youtube.com/watch?v=hWSHtHasJUI

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