Sketch/example pipeline to assemble a multi-arch manifest list based on arch-specific builds in a heterogeneous-arch cluster

multiarch-pipeline.yaml

# This Task runs a `docker build` on a specified node architecture.
# TODO:
# - mount source incl Dockerfile
# - mount a Docker daemon

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: build
spec:
  params:
  - name: arch
    description: CPU architecture to build on
  results:
  - name: ref
  podTemplate:
    nodeSelector:
      kubernetes.io/arch: $(params.arch)
  steps:
  - name: build
    image: docker
    script: |
      docker build -t image:$(params.arch) .
      cat image:$(params.arch) > $(results.ref.path)

---

# This Task combines N image references into a single manifest and pushes it.
# TODO: auth for the push

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: build-manifest
spec:
  params:
  - name: images
    type: array
    description: Images to combine into the manifest
  - name: ref
    description: Ref to give to the manifest
  results:
  - name: IMAGE_DIGEST
  steps:
  - name: build-manifest
    image: docker
    script: |
      docker manifest create $(params.ref) $(params.images[*])
      docker manifest push $(params.ref)

---

# This Pipeline runs N arch-specific builds, then combines their resulting
# images into a manifest list using the above tasks.

apiVersion: tekton.dev/v1beta1
kind: Pipeline
metadata:
  name: multiarch-build
spec:
  tasks:
  - name: build-amd64
    taskRef:
      name: build
    params:
    - name: arch
      value: amd64
  - name: build-arm64
    taskRef:
      name: build
    params:
    - name: arch
      value: arm64
  - name: build-ppc64le
    taskRef:
      name: build
    params:
    - name: arch
      value: ppc64le
  - name: build-s390x
    taskRef:
      name: build
    params:
    - name: arch
      value: s390x

  - name: build-manifest
    taskRef:
      name: build-manifest
    params:
    - name: images
      value:
      - $(tasks.build-amd64.ref)
      - $(tasks.build-arm64.ref)
      - $(tasks.build-ppc64le.ref)
      - $(tasks.build-s390x.ref)
    - name: ref
      value: gcr.io/imjasonh/multiarch