dag-multiroot.yaml

# The following workflow executes a multi-root workflow
# 
#   A   B
#  / \ /
# C   D
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: dag-multiroot-
spec:
  entrypoint: multiroot
  templates:
  - name: echo
    inputs:
      parameters:
      - name: message
    container:
      image: alpine:3.7
      command: [echo, "{{inputs.parameters.message}}"]
  - name: multiroot
    dag:
      tasks:
      - name: A
        template: echo
        arguments:
          parameters: [{name: message, value: A}]
      - name: B
        dependencies:
        template: echo
        arguments:
          parameters: [{name: message, value: B}]
      - name: C
        dependencies: [A]
        template: echo
        arguments:
          parameters: [{name: message, value: C}]
      - name: D
        dependencies: [A, B]
        template: echo
        arguments:
          parameters: [{name: message, value: D}]