How to pass multiple lists in a single loop in argo workflows

I want to pass elements of multiple lists in a single loop using argo templates

I have 3 lists like below

effect = ["Allow", "Allow", "Allow"]
resource = ["*", "*", "*"]
action = ["ec2:CreateTags", "ec2:DescribeInstances", "ec2:AuthorizeSecurityGroupIngress"]

I have a IAM policy which I need to construct with the argo templates. The below IAM policy takes elements from 3 lists in each loop. How can we pass these three lists elements in a single loop?

I referred to argo documentations, there's only withItems/withParams loop is available which takes only one list at a time

I tried the below method but, it is not working

- name: policy
  value: |-
  <<-EOP
  {
    "Effect": "{{item.1}}",
    "Action": "{{item.2}}",
    "Resource": "{{item.3}}"
  }
  EOP
  withTogether:
   - "{{inputs.parameters.effect}}"
   - "{{inputs.parameters.actions}}"
   - "{{inputs.parameters.resources}}"

If it is not supported in argo, is there any alternate way that we can achieve this?

Solution

Don't use withItems/withParams for simple JSON manipulation. Argo Workflows represents each iteration of these loops with at least one Pod. That's slow.

I'd recommend using a familiar programming language and a script template to perform the work.

Argo has a simple, built-in "expressions tag" templating tool which you could use to perform the same mutation.

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: so-69180308-
spec:
  arguments:
    parameters:
      - name: effects
        value: '["Allow", "Allow", "Allow"]'
      - name: resources
        value: '["*", "*", "*"]'
      - name: actions
        value: '["ec2:CreateTags", "ec2:DescribeInstances", "ec2:AuthorizeSecurityGroupIngress"]'
  entrypoint: main
  templates:
    - name: main
      script:
        env:
          - name: POLICIES
            value: >-
              {{=
                toJson(
                  map(
                    0..(len(jsonpath(workflow.parameters['effects'], '$'))-1),
                    {
                      {
                        effect: jsonpath(workflow.parameters['effects'], '$')[#],
                        resource: jsonpath(workflow.parameters['resources'], '$')[#],
                        action: jsonpath(workflow.parameters['actions'], '$')[#]
                      }
                    }
                  )
                )
              }}
        image: debian:9.4
        command: [bash]
        source: |
          echo "$POLICIES"

Output:

[{"action":"ec2:CreateTags","effect":"Allow","resource":"*"},{"action":"ec2:DescribeInstances","effect":"Allow","resource":"*"},{"action":"ec2:AuthorizeSecurityGroupIngress","effect":"Allow","resource":"*"}]

I'd recommend against going the expression tag route. It's a less well-known language and will be more difficult for others to maintain.