It's not always clear that pure JSON must be used for the parameters. If you make a mistake, the deployment will fail but it will become impossible to modify the parameter again.
Steps to reproduce
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1. Pick an option, e.g. CephStorageConfig
2. Enter something wrong, e.g. the way you'd have made the change for a template: ceph::profile::params::osds:
'/dev/sdc':
journal: '/dev/sdb'
Expected result
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3. Some kind of warning, the wrong value is not saved in the Mistral environment
Actual result
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3. The value is saved.
4. If you try to deploy, it fails with Failed to run action [action_ex_id=00e7c638-4741-4b79-a760-edfafb190cac, action_cls='<class 'mistral.actions.action_factory.DeployStackAction'>', attributes='{}', params='{u'container': u'master-tht-oct19', u'timeout': 240}'] ERROR: Failed to validate: Failed to validate: resources[0]: Value must be valid JSON: No JSON object could be decoded
5. If you reopen the parameters window, it closes quickly on its own before you can modify it, with the following error: Failed to run action [action_ex_id=None, action_cls='<class 'mistral.actions.action_factory.GetParametersAction'>', attributes='{}', params='{u'container': u'master-tht-oct19'}'] ERROR: Value must be valid JSON: No JSON object could be decoded
This is what the parameter looks like in the mistral environment, after saving the wrong parameter:
"CephStorageExt