The easiest way to start taking advantage of CUE’s powerful validation is to use it to check existing configuration files. By adding this check to your development or deployment process you can catch and fix errors before they affect downstream systems.

This guide shows you how to use the cue command to validate an Argo workflow file using a curated module from the CUE Central Registry – all without writing any schemas or policies in CUE.

The latest pre-release of the cue command is required – please upgrade to this version if it’s not already installed:

$ cue version
cue version v0.13.0-alpha.3
...

Login to the Central Registry

$ cue login # only during beta

The Central Registry requires authentication while it’s in beta testing, so you need to login before you can use its schemas.

Choose an Argo workflow file

This example comes from the Argo Workflows project, but you should use any Argo workflow file that’s relevant to your situation.

# filepath: workflow.yml

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: arguments-parameters-
spec:
  entrypoint: print-message
  arguments:
    parameters:
    - name: message
      value: hello world
  templates:
  - name: print-message
    inputs:
      parameters:
      - name: message
    container:
      image: busybox
      command: [echo]
      args: ["{{inputs.parameters.message}}"]

Validate the workflow file

$ cue vet -c -d '#Workflow' cue.dev/x/argocd@latest workflow.yml

This command uses the #Workflow definition from the argocd package to check the workflow.yml file. Because cue vet doesn’t display any errors, you know that the curated module has validated your configuration file.

Next steps

Validating your existing configuration files with CUE can help make development and deployments safer, but defining those same files in CUE lets you build on its first-class templating, referencing, and policy features. Take the first step with Getting started with Argo Workflows + CUE …