How to convert amd64 docker image to multi-arch

 To convert an existing amd64 Docker image into a multi-architecture (multiarch) image that supports platforms like linux/amd64 and linux/arm64, you need to use docker buildx.

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✅ Steps to Create a Multi-Arch Docker Image

1. Enable experimental features and create a buildx builder

docker buildx create --use --name multiarch-builder
docker buildx inspect --bootstrap

✅ This ensures you can build images for multiple platforms in one go.

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2. Build and push a multiarch image

If you're pushing to a registry (e.g., Docker Hub or ECR):

docker buildx build \
  --platform linux/amd64,linux/arm64 \
  -t <your-registry>/<image-name>:<tag> \
  --push .

Example:

docker buildx build \
  --platform linux/amd64,linux/arm64 \
  -t myuser/myapp:latest \
  --push .

🧠 --push is required for multiarch images since they’re built in a remote context.

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3. (Optional) Test locally

To load for local testing (only works for one platform at a time):

docker buildx build --platform linux/amd64 -t myimage:local --load .

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✅ Verify Multi-Arch Support

After building and pushing, inspect the image:

docker buildx imagetools inspect <your-registry>/<image-name>:<tag>

Expected output should include something like:

"manifests": [
  {
    "platform": {
      "architecture": "amd64",
      "os": "linux"
    },
    ...
  },
  {
    "platform": {
      "architecture": "arm64",
      "os": "linux"
    },
    ...
  }
]

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📌 Notes

• You must be logged into your registry (e.g., Docker Hub) to push.

• You must use buildx and --push to generate multi-platform manifests.

• The Dockerfile itself must not include architecture-specific binaries unless you're handling them with conditional logic (e.g., downloading binaries for the right TARGETARCH).