Confusion around withItems vs withParam

[max-sixty]

I became very confused when working through some parallelization, and I wanted to confirm my understanding and offer some guidance for others who might get confused.

Since working through a withParam workflow, IIUC, withParam is not the same as withItems in that:

• withItems creates n tasks for both that task and any of its dependencies.
• withParam creates n tasks for only that task. Its dependencies will have a count of 1 regardless of how many instances of the original task are created (unless they create multiple instances of themselves using withItems or withParam.

Is this correct?

Thanks!

[DimitrisSotiriou]

I'm not experienced with Argo alot, but browsing to the provided examples my understanding is that withParam is used when the values are produced from different template within the workflow. Not 100% sure though

[max-sixty]

I was Googling this question just now, and found my old question!

I still don't have a great understanding, but for the sake of posterity, the main difference seems to be:

• withParam takes a json string; generally passed by a previous task
• withItems takes a yaml list; all the examples have this inlined into the template

[padrepitufo]

Was also in search of the difference, I found something that confirms what you're saying here https://argoproj.github.io/argo-workflows/fields/ which has

[wesleyscholl]

@max-sixty @DimitrisSotiriou @padrepitufo

The main differences between withItems and withParam in Argo Workflows:

Data source:

• withItems uses a YAML list defined directly in the workflow template.
• withParam takes a JSON string, typically passed from a previous step or template.

Use case:

• withItems is used for static, predefined lists.
• withParam is more flexible and can handle dynamically generated lists.

This functional workflow demonstrates both withItems and withParam:

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: withitems-withparam-random-
  namespace: argo
spec:
  templates:
    - name: main
      steps:
        - - name: generate-random-list
            template: random-list-generator
        - - name: withitems-example
            template: print-message
            arguments:
              parameters:
                - name: message
                  value: '{{item}}'
            withItems:
              - Hello
              - World
        - - name: withparam-example
            template: print-message
            arguments:
              parameters:
                - name: message
                  value: '{{item}}'
            withParam: '{{steps.generate-random-list.outputs.result}}'
    - name: random-list-generator
      script:
        name: ''
        image: python:alpine3.6
        command:
          - python
        source: |
          import json
          import random
          import string

          def random_string(length):
              return ''.join(random.choices(string.ascii_lowercase, k=length))

          num_strings = random.randint(3, 10)
          random_list = [random_string(5) for _ in range(num_strings)]
          print(json.dumps(random_list))
    - name: print-message
      inputs:
        parameters:
          - name: message
      container:
        name: ''
        image: alpine:3.14
        command:
          - echo
        args:
          - '{{inputs.parameters.message}}'
  entrypoint: main

Resources:

• Argo Workflows Loops - https://argo-workflows.readthedocs.io/en/latest/walk-through/loops/
• Field Reference - https://argo-workflows.readthedocs.io/en/latest/fields/#workflowstep