Conditionals

We also support conditional execution. The syntax is implemented by govaluate which offers the support for complex syntax. See in the example:

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: coinflip-
spec:
  entrypoint: coinflip
  templates:
  - name: coinflip
    steps:
    # flip a coin
    - - name: flip-coin
        template: flip-coin
    # evaluate the result in parallel
    - - name: heads
        template: heads                       # call heads template if "heads"
        when: "{{steps.flip-coin.outputs.result}} == heads"
      - name: tails
        template: tails                       # call tails template if "tails"
        when: "{{steps.flip-coin.outputs.result}} == tails"
    - - name: flip-again
        template: flip-coin
    - - name: complex-condition
        template: heads-tails-or-twice-tails
        # call heads template if first flip was "heads" and second was "tails" OR both were "tails"
        when: >-
            ( {{steps.flip-coin.outputs.result}} == heads &&
              {{steps.flip-again.outputs.result}} == tails
            ) ||
            ( {{steps.flip-coin.outputs.result}} == tails &&
              {{steps.flip-again.outputs.result}} == tails )
      - name: heads-regex
        template: heads                       # call heads template if ~ "hea"
        when: "{{steps.flip-again.outputs.result}} =~ hea"
      - name: tails-regex
        template: tails                       # call heads template if ~ "tai"
        when: "{{steps.flip-again.outputs.result}} =~ tai"

  # Return heads or tails based on a random number
  - name: flip-coin
    script:
      image: python:alpine3.6
      command: [python]
      source: |
        import random
        result = "heads" if random.randint(0,1) == 0 else "tails"
        print(result)

  - name: heads
    container:
      image: alpine:3.6
      command: [sh, -c]
      args: ["echo \"it was heads\""]

  - name: tails
    container:
      image: alpine:3.6
      command: [sh, -c]
      args: ["echo \"it was tails\""]

  - name: heads-tails-or-twice-tails
    container:
      image: alpine:3.6
      command: [sh, -c]
      args: ["echo \"it was heads the first flip and tails the second. Or it was two times tails.\""]

Note

If the parameter value contains quotes, it may invalidate the govaluate expression. To handle parameters with quotes, embed an expr expression in the conditional. For example:

when: "{{=inputs.parameters['may-contain-quotes'] == 'example'}}"

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