A concrete failure case for https://github.com/argoproj/argo/pull/1651

parameter-aggregation-template.yaml

# Example workflow to demonstrate parameter aggregation.
apiVersion: argoproj.io/v1alpha1
kind: WorkflowTemplate
metadata:
  name: parameter-aggregation-template
spec:
  templates:
  # odd-or-even accepts a number and returns whether or not that number is odd or even
  - name: odd-or-even
    inputs:
      parameters:
      - name: num
    container:
      image: alpine:latest
      command: [sh, -xc]
      args:
      - |
        sleep 1 &&
        echo {{inputs.parameters.num}} > /tmp/num &&
        if [ $(({{inputs.parameters.num}}%2)) -eq 0 ]; then
          echo "even" > /tmp/even;
        else
          echo "odd" > /tmp/even;
        fi
    outputs:
      parameters:
      - name: num
        valueFrom:
          path: /tmp/num
      - name: evenness
        valueFrom:
          path: /tmp/even

  # divide-by-2 divides a number in half
  - name: divide-by-2
    inputs:
      parameters:
      - name: num
    script:
      image: alpine:latest
      command: [sh, -x]
      source: |
        #!/bin/sh
        echo ready
        sleep 30
        echo $(({{inputs.parameters.num}}/2))

parameter-aggregation.yaml

# Example workflow to demonstrate parameter aggregation.
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: parameter-aggregation-
spec:
  entrypoint: parameter-aggregation
  templates:
  - name: parameter-aggregation
    steps:
    # First loop through a list of numbers and determine if the number is odd or even. This is
    # captured in output parameter 'evenness'. (e.g. {"num": "4", "evenness": "even"})
    - - name: odd-or-even
        templateRef:
          name: parameter-aggregation-template
          template: odd-or-even
        arguments:
          parameters:
          - name: num
            value: "{{item}}"
        withItems: [1, 2, 3, 4]
    # Next, for each even number, divide it by two (using a script template).
    # Skip odd numbers using a `when` clause.
    - - name: divide-by-2
        templateRef:
          name: parameter-aggregation-template
          template: divide-by-2
        arguments:
          parameters:
          - name: num
            value: "{{item.num}}"
        withParam: "{{steps.odd-or-even.outputs.parameters}}"
        when: "{{item.evenness}} == even"
    # Finally, print all numbers processed in the previous step
    - - name: print
        template: whalesay
        arguments:
          parameters:
          - name: message
            value: "{{item}}"
        withParam: "{{steps.divide-by-2.outputs.result}}"
  # whalesay prints a number using whalesay
  - name: whalesay
    inputs:
      parameters:
      - name: message
    container:
      image: docker/whalesay:latest
      command: [cowsay]
      args: ["{{inputs.parameters.message}}"]

$ argo template create parameter-aggregation-template.yaml
$ argo submit parameter-aggregation.yaml
# Wait for the workflow until divide-by-2 pods emit `ready`.
$ argo delete template parameter-aggregation-template
# Wait for 30 seconds
$ argo get parameter-aggregation-msfrr
Name:                parameter-aggregation-msfrr
Namespace:           default
ServiceAccount:      default
Status:              Error
Message:             workflow template parameter-aggregation-template not found
Created:             Mon Oct 07 14:35:34 +0900 (2 minutes ago)
Started:             Mon Oct 07 14:35:34 +0900 (2 minutes ago)
Finished:            Mon Oct 07 14:36:18 +0900 (1 minute ago)
Duration:            44 seconds

STEP                                                                                    PODNAME                                 DURATION  MESSAGE
 ⚠ parameter-aggregation-msfrr (parameter-aggregation)                                                                                    workflow template parameter-aggregation-template not found
 ├-·-✔ odd-or-even(0:1) (parameter-aggregation-template/odd-or-even)                    parameter-aggregation-msfrr-4106064204  15s
 | ├-✔ odd-or-even(1:2) (parameter-aggregation-template/odd-or-even)                    parameter-aggregation-msfrr-4201720470  18s
 | ├-✔ odd-or-even(2:3) (parameter-aggregation-template/odd-or-even)                    parameter-aggregation-msfrr-2072260708  20s
 | └-✔ odd-or-even(3:4) (parameter-aggregation-template/odd-or-even)                    parameter-aggregation-msfrr-2708307642  23s
 └-·-○ divide-by-2(0:evenness:odd,num:1) (parameter-aggregation-template/divide-by-2)                                                     when 'odd == even' evaluated false
   ├-● divide-by-2(1:evenness:even,num:2) (parameter-aggregation-template/divide-by-2)  parameter-aggregation-msfrr-4023672552  1m
   ├-○ divide-by-2(2:evenness:odd,num:3) (parameter-aggregation-template/divide-by-2)                                                     when 'odd == even' evaluated false
   └-● divide-by-2(3:evenness:even,num:4) (parameter-aggregation-template/divide-by-2)  parameter-aggregation-msfrr-2970660232  1m