[BUG] Policy with CRON transition: [illegal_argument_exception] Unknown schedule type expression

[davide-malagoli]

Describe the bug
I'm trying to define a policy that deletes an "old" index at midnight.

I'm using Opendistro 1.4 and from the documentation I see it would be possible to use CRON expressions ( Transitions )

But when I try t save it gives me an error

[illegal_argument_exception] Unknown schedule type expression

Other plugins installed
No other plugin installed

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Index Management'
2. Click on 'Create Policy'
3. Insert 'delete_at_midnight' in the 'Policy ID' field
4. Paste the following definition

 {
    "policy": {
        "policy_id": "delete_at_midnight",
        "description": "A simple default policy that deletes old indicies after 1 days.",
        "default_state": "open",
        "states": [
            {
                "name": "open",
                "actions": [
                    {
                        "open": {}
                    }
                ],
                "transitions": [
                    {
                        "state_name": "delete",
                        "conditions": {
                            "cron": {
                                "expression":"1 0 * * *",
                                "timezone":"CET"
                            }
                        }
                    }
                ]
            },
            {
                "name": "delete",
                "actions": [
                    {
                        "delete": {}
                    }
                ],
                "transitions": []
            }
        ]
    }
}

5. See error

Expected behavior
Kibana saves the policy

Desktop (please complete the following information):

• OS: Ubuntu 18.04.4 LTS
• Browser: chrome
• Version 81.0.4044.92

[dbbaughe]

Hi @davide-malagoli,

Seems like our syntax got a little screwed up with the parsers.
You'll have to do something like:

{
  "cron": {
    "cron": {
      ...
    }
  }
}

We'll fix it so the single "cron" object works and keep this way just to make sure it doesn't break for anyone that had to write it this way for future versions.