Argo: Workflows should be able to reference WorkflowTemplates entirely without templates

[sarabala1979]

Summary

Workflow-template need to be submitted periodically through Cron-Workflow

Motivation

In v2.7, templateRef has been removed from the template and the submittable workflowtemplate feature has been added. It would be a good feature to support the cron workflow to submit the workflow template periodically. This feature will enable the use-case to change the workflow definition without changing/resubmitting cronworkflow.

Please give examples of your use case, e.g. when would you use this.

Proposal

kind: CronWorkflow
metadata:
  name: hello-world
spec:
  schedule: "* * * * *"
  timezone: "America/Los_Angeles"  
  startingDeadlineSeconds: 0
  concurrencyPolicy: "Replace"      # Default to "Allow"
  successfulJobsHistoryLimit: 4     # Default 3
  failedJobsHistoryLimit: 4         # Default 1
  suspend: false                    # Set to "true" to suspend scheduling
  workflowTemplateRef:
    name: workflow-template-submittable

How do you think this should be implemented?

---

Message from the maintainers:

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[simster7]

While template.tempalteRef was deprecated, template.steps.templateRef and template.dag.task.templateRef weren't. Calling a WorkflowTemplate from a Workflow is still very much possible, it just needs to be done inside steps or dag.

apiVersion: argoproj.io/v1alpha1
kind: CronWorkflow
metadata:
  name: hello-world
spec:
  schedule: "* * * * *"
  workflowSpec:
    entrypoint: whalesay
    templates:
      - name: whalesay
        steps:
          - - name: call-whalesay-template
              templateRef:
                name: workflow-template-whalesay-template
                template: whalesay-template
              arguments:    # Inputs should be converted to arguments
                parameters:
                - name: message
                  value: Hello, world

[sarabala1979]

I think it is a workaround. let's discuss and get feedback from users and team

[danxmoran]

FWIW, as somebody who just converted a bunch of existing CronWorkflows from using template.templateRef to using template.steps.templateRef, I'd 100% re-convert them back to using a dedicated top-level workflowTemplateRef field if that became an option. The extra syntactic noise of the steps is annoying, and it makes it tempting to add more logic there (vs. a top-level ref, which I feel pretty clearly indicates that all "real" logic should be in the template). I would need to be able to pass arguments to the top-level ref, though.

Alt: If WorkflowTemplate was extended to also support specifying all of CronWorkflow's scheduling parameters, that would be even better / cleaner IMO.

[jessesuen]

The extra syntactic noise of the steps is annoying, and it makes it tempting to add more logic there (vs. a top-level ref, which I feel pretty clearly indicates that all "real" logic should be in the template).

This is exactly my sentiment as well.

spec:
  workflowTemplateRef:
    name: workflow-template-submittable

Can we make sure that it is possible for Argo Events to also follow the proposed syntax?

I would need to be able to pass arguments to the top-level ref, though.

Agree, we need to make sure this is supported as well.

[sarabala1979]

Thanks @jessesuen I will create an Issue in Argo Event and contribute it.

[simster7]

I think this would be good if it were implemented at the Workflow level (instead of the CronWorkflow).

Currently the only way to submit a WorkflowTemplate is through the CLI, which converts it directly to a Workflow. If a WorkflowTemplate is actually a _definition_ of a Workflow, it should be possible for it to be instanciated on a Workflow object.

Perhaps by

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  name: test
spec:
  workflowTemplateRef:
    name: workflow-template-name
  arguments:
    parameters:
      - name: message
        value: "Hello, world"

That would allow a CronWorkflow to instantiate a WorkflowTempalte like so:

apiVersion: argoproj.io/v1alpha1
kind: CronWorkflow
metadata:
  name: hello-world
spec:
  schedule: "* * * * *"
  workflowSpec:
    workflowTemplateRef:
      name: workflow-template-name
    arguments:
      parameters:
        - name: message
          value: "Hello, world"

I fear that implementing the original suggestion would tangle all CronWorkflows, WorkflowTemplates, and Workflows together. I think the Workflow should be the only resource able to reference other resources (with the exception of WorkflowTemplates referencing themselves).

I would need to be able to pass arguments to the top-level ref, though.

Agree, we need to make sure this is supported as well.

I actually have some reservations about this, and about WorkflowTemplates having Arguments in general. I am hoping to discuss this internally today and create an issue after gathering feedback.

[danxmoran]

Implementing at the Workflow level makes sense to me as a user :+1:

I actually have some reservations about this, and about WorkflowTemplates having Arguments in general. I am hoping to discuss this internally today and create an issue after gathering feedback.

Having the ability to pass inputs to the entrypoint of the template is critical to my use-case, but I think we might be talking about two separate things. I'll comment on the other issue to clarify.

[simster7]

Having the ability to pass inputs to the entrypoint of the template is critical to my use-case, but I think we might be talking about two separate things. I'll comment on the other issue to clarify.

Correct, two different things 🙂

To be super clear, I meant that WorkflowTemplates shouldn't be able to define Arguments in its own definition. Arguments should be passed into a WorkflowTemplate from its caller. #2559 is opened to address this.

[simster7]

For the submittable WorkflowTemplates PR, I think we should use the existing templateRef field. Something like

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  name: test
spec:
  templateRef:
    name: workflow-template-name
  arguments:
    parameters:
      - name: message
        value: "Hello, world"

templateRef without templateRef.tempalte set can indicate a WorkflowTemplate as a whole. This could be used to submit full WorkflowTemplates for anywhere else in the Workflow (such as steps or dag)

[lbjarre]

Just want to chime in as a user to say that I agree with the discussion so far and like the proposal!

Any updates on the status? Judging from some recent activity it seems that this has already been merged, but I can't find the specific PR (if it exists).

[simster7]

Merged in https://github.com/argoproj/argo/pull/2912