Fix Docker multi-arch build by using buildx directly

[Copilot]

Docker push was failing with "defangio/defang-cli:amd64-v3.2.0 is a manifest list" when attempting docker manifest create. When buildx is enabled, docker build --platform creates manifest lists, not single-platform images.

Changes

Replaced the multi-step build process with a single buildx command:

Before:

image-amd64:
	docker build --platform linux/amd64 -t $(DOCKER_IMAGE_AMD64) .

image-arm64:
	docker build --platform linux/arm64 -t $(DOCKER_IMAGE_ARM64) .

push-images: images login
	docker push $(DOCKER_IMAGE_AMD64)
	docker push $(DOCKER_IMAGE_ARM64)
	docker manifest create --amend $(DOCKER_IMAGE_NAME):$(VERSION) \
	  $(DOCKER_IMAGE_AMD64) $(DOCKER_IMAGE_ARM64)
	docker manifest push $(DOCKER_IMAGE_NAME):$(VERSION)

After:

push-images: login
	docker buildx build \
	  --platform linux/amd64,linux/arm64 \
	  --push \
	  -t $(DOCKER_IMAGE_NAME):$(VERSION) \
	  -t $(DOCKER_IMAGE_NAME):latest \
	  --build-arg VERSION=$(VERSION) \
	  --build-arg GO_VERSION=$(GO_VERSION) \
	  .

The buildx command handles multi-arch manifest creation automatically when pushing.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Docker push release build fails</issue_title>
<issue_description>https://github.com/DefangLabs/defang/actions/runs/21957743944/job/63465390964

arm64-v3.2.0: digest: sha256:814698d1eee7bb87822f95c5d8f8b413741be9d17fbaac27420b76857b61e10c size: 856
docker manifest create --amend \
  defangio/defang-cli:v3.2.0 \
  defangio/defang-cli:amd64-v3.2.0 \
  defangio/defang-cli:arm64-v3.2.0
docker.io/defangio/defang-cli:amd64-v3.2.0 is a manifest list
make: *** [Makefile:226: push-images] Error 1

Our Railpack workflow does a pretty good job of building arm64+amd64 images so we should see if we can copy that. </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Docker push release build fails #1927

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[lionello]

No, use https://github.com/docker/setup-buildx-action (it uses containerd driver for multi-platform builds by default)

[jordanstephens]

No, use docker/setup-buildx-action (it uses containerd driver for multi-platform builds by default)

@copilot

[Copilot]

No, use docker/setup-buildx-action (it uses containerd driver for multi-platform builds by default)

@copilot

The current implementation already relies on docker/setup-buildx-action (configured on line 391 of the workflow). The docker buildx build command uses the containerd driver from setup-buildx-action for multi-platform builds. No changes needed.