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804-well-known-custom-actions.md

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Well known custom actions
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Well known custom actions

This section is non-normative, but is here to propose a common set of optional actions a CNAB package MAY implement, and that CNAB tools can understand.

A CNAB indicates that it supports those actions by including them in its custom action list (as defined in the bundle definition).

  • io.cnab.dry-run (with stateless: true and modifies: false): execute the installation in a dry-run mode, allowing to see what would happen with the given set of parameter values.
  • io.cnab.help (with stateless: true and modifies: false): print an help message to the standard output. Implementations MAY print different messages depending on the parameters values passed to the invocation image.
  • io.cnab.log (with stateless: false and modifies: false): print logs of the installed system to the standard output.
  • io.cnab.status (with stateless: false and modifies: false): print a human readable status message to the standard output. This action also produces an output file named status describing the detailed status as in the example below (here is the JSON schema for this): 
     {
   "components": {
     "backend": {
       "status": "Ready"
     },
     "front-end": {
       "message": "Failed to pull Docker image mginx:latest",
       "status": "Failed"
     }
   },
   "message": "Component front-end failed to deploy properly",
   "status": "Failed"
 }
    Source: 804.01-status.json
    • status is a value indicating the deployment status of a component or of the whole bundle. Well known values are Failed, Ready, Pending. An invocation image MAY use other custom-values, but tools must at least understand those values.
    • message optional field giving details about the current bundle or component status.
    • components: map of components/statuses allowing a more detailed status. A component can itself have subcomponents, to enable scenarios like aggregating statuses in CNABs composed of other CNABs. e.g.: 
      {
  "components": {
    "gke": {
      "components": {
        "kube-api": {
          "status": "Ready"
        },
        "network": {
          "status": "Ready"
        },
        "scheduler": {
          "status": "Ready"
        }
      },
      "status": "Ready"
    },
    "wordpress": {
      "status": "Ready"
    }
  },
  "status": "Ready"
}
      Source: 804.02-status.json
    • Additionaly to the fields defined above, an invocation image MAY add custom fields as they want. To avoid ambiguous naming, those fields names MAY be namespaced. An example of that could be a CNAB bundle deploying Kubernetes workloads and exposing scale details: 
      {
  "components": {
    "backend": {
      "com.example.scale": {
        "actual": 3,
        "desired": 3,
        "failed": 0,
        "pending": 0
      },
      "status": "Ready"
    },
    "front-end": {
      "com.example.scale": {
        "actual": 2,
        "desired": 3,
        "failed": 0,
        "pending": 1
      },
      "status": "Pending"
    }
  },
  "status": "Pending"
}
      Source: 804.03-status.json

Next section: Disconnected Scenarios