json_schema: {
      "$schema": "http://json-schema.org/draft-04/schema#",
      "title": "cloud-init plugin manifest",
      "type": "object",
      "properties": {
          "system": {
              "type": "object",
              "properties": {
                  "release": {
                      "type": "string",
                      "enum": [
                          "wheezy",
                          "stable",
                          "jessie",
                          "testing",
                          "sid",
                          "unstable"
                      ]
                  }
              }
          },
          "plugins": {
              "type": "object",
              "properties": {
                  "cloud_init": {
                      "type": "object",
                      "properties": {
                          "username": {
                              "type": "string"
                          },
                          "disable_modules": {
                              "type": "array",
                              "items": {
                                  "type": "string"
                              },
                              "_uniqueItems": true
                          },
                          "metadata_sources": {
                              "type": "string"
                          }
                      },
                      "required": [
                          "username"
                      ]
                  },
                  "packages": {
                      "type": "object"
                  }
              },
              "required": [
                  "cloud_init"
              ]
          }
      }
  }