Support for >=, <=, >, < conditionals.

[vicaire]

Is this a BUG REPORT or FEATURE REQUEST?: FEATURE REQUEST

Argo conditionals seem to only support "==":

https://github.com/argoproj/argo/blob/master/examples/conditionals.yaml

Would it make sense to add support for additional operations such as >=, <=, >, <?

For instance, in a machine learning context:

• One step computes a model
• The model is stored in an object store
• the step outputs the accuracy of the model.
• We could then use the ">=" to express that the workflow should proceed to the next step only if the accuracy of the model is greater than X.

[vicaire]

@qimingj

[jessesuen]

Would it make sense to add support for additional operations such as >=, <=, >, <?

Yes. The conditional parsing in Argo is extremely dumb at the moment. To go even further, we should support grouping with parens. Kubernetes already provides a very nice parsing library for this:
"k8s.io/apimachinery/pkg/labels"

This library is already being used in Argo's resource templates to support success conditions and failure conditions, but has not yet made its way in the controller conditional evaluation logic.

[vicaire]

Grouping with parens? Would that be to support multiple output parameters?

[jessesuen]

Right. You should be able to do something like:
(foo == true) && (bar == true)

[jessesuen]

Implemented in 9b5c856 using the library: https://github.com/Knetic/govaluate. Here are some examples of what is now supported:

		"foo == foo",
		"foo != bar",
		"1 == 1",
		"1 != 2",
		"1 < 2",
		"1 <= 1",
		"a < b",
		"(foo == bar) || (foo == foo)",
		"(1 > 0) && (1 < 2)",
		"Error in (Failed, Error)",
		"!(Succeeded in (Failed, Error))",
		"true == true",

[vicaire]

Thanks jessesuen!

[sylock]

The implemented functionality is really nice but the documentation should be upgraded to explain it. Currently the documentation is very poor about it. You only have :

• a reference in the beginner core concept: https://argoproj.github.io/argo-workflows/workflow-concepts/#template-invocators
• one example that does not explain all the possibilities: https://argoproj.github.io/argo-workflows/examples/#conditionals

In conclusion: this current issue is the only place where you can find a good documentation about the conditionals syntax.

[simster7]

@sylock Thanks! Would you like to submit a PR with better documentation about this?

[julien-blanchon]

I didn't manage to make this work using 👍

when: {{steps.predict.outputs.artifacts.score}}"

I get the following workflow error:

Invalid 'when' expression '{{steps.predict.outputs.artifacts.score}} > 0.5': Invalid token: '{{' (hint: try wrapping the affected expression in quotes ("))