How to parameterize a workflowTempateRef? - argoproj

Question

I have a WorkflowTemplate "nyc-test-template" which I trigger via Argo Events and PubSub. So, if I publish a message {} into the PubSub topic "argo-events-nyc" the template specified via a workflowTempateRef is started. That does work just fine. Now I want to parameterize the to be started template.
My not-working draft looks as follows:
apiVersion: argoproj.io/v1alpha1
kind: EventSource
metadata:
name: pubsub-event-source-nyc
spec:
template:
serviceAccountName: argo-events
pubSub:
examplex:
jsonBody: true
topic: argo-events-nyc
subscriptionID: argo-events-nyc-sub
---
apiVersion: argoproj.io/v1alpha1
kind: Sensor
metadata:
name: pubsub-sensor-nyc
spec:
template:
serviceAccountName: argo-events-sa
dependencies:
- name: pubsub-event-source-dep
eventSourceName: pubsub-event-source-nyc
eventName: examplex
triggers:
- template:
name: argo-workflow-trigger
argoWorkflow:
group: argoproj.io
version: v1alpha1
resource: workflows
operation: submit
source:
resource:
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
generateName: nyc-test-template-
namespace: argo
spec:
arguments:
parameters:
- name: wft
value: nyc-test-template
workflowTemplateRef:
# I'm pretty sure this inputs block is useless. But leaving it out
# and instead referencing arguments.parameters.wft won't work either.
inputs:
parameters:
- name: wft
name: "{{inputs.parameters.wft}}"
parameters:
- src:
dependencyName: pubsub-event-source-dep
dataKey: body.wft
dest: spec.arguments.parameters.0.value
What I would like to happen is this:
an empty message {} would trigger "nyc-test-template"
the message {"wft": "my-template"} would trigger "my-template"
Instead publishing an empty message will cause the Sensor to throw an error:
2021-03-29T15:31:16.386441528Z2021/03/29 15:31:16 Failed to parse workflow: error unmarshaling JSON: while decoding JSON: json: unknown field "inputs"
Frankly speaking - above yaml took crude inspiration from this example. It's not really the result of an educated guess as I still don't understand the mechanics of how parameters, arguments and inputs are interacting.

Answer 1

You can use when to toggle which template to use depending on a parameter.
Suppose I have two simple WorkflowTemplates like these:
apiVersion: argoproj.io/v1alpha1
kind: WorkflowTemplate
metadata:
name: t1
spec:
templates:
- name: whalesay-template
container:
image: docker/whalesay
command: [cowsay]
args: [t1]
---
apiVersion: argoproj.io/v1alpha1
kind: WorkflowTemplate
metadata:
name: t2
spec:
templates:
- name: whalesay-template
container:
image: docker/whalesay
command: [cowsay]
args: [t2]
I can choose to execute one or another template from the WorkflowTemplates depending on an argument passed to a Workflow (either manually or from an argo-events setup).
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
generateName: switch-
spec:
entrypoint: pick
arguments:
parameters:
- name: which
templates:
- name: pick
steps:
- - name: t1
when: "{{workflow.parameters.which}} == t1"
templateRef:
name: t1
template: whalesay-template
- name: t2
when: "{{workflow.parameters.which}} == t2"
templateRef:
name: t2
template: whalesay-template
For top-level arguments to a Workflow, you can use workflow.parameters.SOMETHING.
Building on the above, you can use a JSON parsing tool like jq to retrieve toggle value and then choose your template based on that value.
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
generateName: switch-
spec:
entrypoint: pick
arguments:
parameters:
- name: json
templates:
- name: pick
steps:
- - name: parse
template: parse
- - name: t1
when: "{{steps.parse.outputs.result}} == a"
templateRef:
name: t1
template: whalesay-template
- name: t2
when: "{{steps.parse.outputs.result}} == b"
templateRef:
name: t2
template: whalesay-template
- name: parse
container:
image: jorgeandrada/alpine-jq
command: [sh, -c]
env:
- name: JSON
value: "{{workflow.parameters.json}}"
args: [echo "$JSON" | jq -j '.test']
I should mention that using jq is a bit heavy-handed. In future versions of Argo (3.1+) there will be tools to inspect JSON more directly. But this solution is nicely reverse-compatible.

Answer 2

Credits go to Derek Wang.
apiVersion: argoproj.io/v1alpha1
kind: Sensor
metadata:
name: pubsub-sensor-nyc
spec:
template:
serviceAccountName: argo-events-sa
dependencies:
- name: pubsub-event-source-dep
eventSourceName: pubsub-event-source-nyc
eventName: examplex
triggers:
- template:
name: argo-workflow-trigger
argoWorkflow:
group: argoproj.io
version: v1alpha1
resource: workflows
operation: submit
source:
resource:
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
generateName: nyc-test-template-
namespace: argo
spec:
workflowTemplateRef:
name: nyc-test-template
parameters:
- src:
dependencyName: pubsub-event-source-dep
dataKey: body.wft
value: nyc-test-template # default value
dest: spec.workflowTemplateRef.name # <- this