You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 11 Next »

Overview

The following page discusses about two proposed standards for Delta report:

Open Questions/Issues/Decisions

Questions/IssuesNotesDecisions
  • Are there any major advantages of using RFC 9144?
  • Does it have major differences when compared to RFC6902?
  • Can it be modified as per requirements of CPS? For example using xpath format


The documentation of RFC 9144 defines a POST operation to find the delta.

  • Does this mean this approach intends to persist the Delta generated to a database?
    • If so will it be an indefinite persistence of delta report or will the delta be removed from storage after a specific time period.

Sample POST request from RFC9144 
POST /restconf/operations/ietf-nmda-compare:compare HTTP/1.1
Host: example.com
Content-Type: application/yang-data+json
Accept: application/yang-data+json

{ "ietf-nmda-compare:input" : {
   "source" : "ietf-datastores:operational",
   "target" : "ietf-datastores:intended",
   "report-origin" : null,
   "xpath-filter" : "/ietf-interfaces:interfaces"
   }
}

The current approach that is being used for development of Delta feature in CPS is a GET operation with no intention to persist the delta report.

It is meant to return the delta in following JSON format.

Sample delta report format 
[
  {
    "action": "ADD",
    "xpath": "/bookstore/categories/[@code=3]",
    "payload": {
      "code": 3,
      "name": "kidz"
    }
  },
  {
    "action": "DELETE",
    "xpath": "/bookstore/categories/[@code=1]",
    "payload": {
      "code": 1,
      "name": "Fiction"
    }
  },
  {
    "action": "UPDATE",
    "xpath": "/bookstore/categories/[@code=2]",
    "payload": {
      "name": "Comic"
    }

  • RFC 9144 defines a yang data model which will be helpful when persisting the Delta Report,
  • But if we go with the approach where the generated delta is not persisted then what will be the benefit of using the model?

  • Are we following any RFC specifications for PATCH operation? 

Intention of RFC 9144

RFC 9144 YANG data model that defines RPCs intended to be used in conjunction with NETCONF [RFC6241] or RESTCONF [RFC8040]. These RPCs allow a client to request a server to compare two NMDA datastores and report any differences.

RFC 9144 Data Model and RFC6902 JSON Patch format

  • The core of the RFC 9144 solution is a new management operation, <compare>, that compares the data tree contents of two datastores. The operation checks whether there are any differences in values or in data nodes that are contained in either datastore and returns any differences as output. The output is returned in the format specified in YANG Patch [RFC8072].
  • The RFC6902 approach to Delta report generation follows the JSON patch format. A JSON Patch document represents an array of objects, where each object contains exactly one operation, path and associated values. The operation can have following values: add, remove, replace, move, copy and test. The path represents the JSON patch and the values contain the difference in source and target values.
    Brief summary of JSON patch can be found in the following page: CPS Delta: Conventions to be used for Delta Report
Example Delta generated as part of RFC9144Example JSON Patch document, transferred in an HTTP PATCH request:
Sample delta as per RFC9144 
{ "ietf-nmda-compare:output" : {
    "differences" : {
      "ietf-yang-patch:yang-patch" : {
        "patch-id" : "interface status",
        "comment" : "diff between intended (source) and operational",
        "edit" : [
          {
            "edit-id" : "1",
            "operation" : "replace",
            "target" : "/ietf-interfaces:interface=eth0/enabled",
            "value" : {
               "ietf-interfaces:interface/enabled" : "false"
            },
            "source-value" : {
               "ietf-interfaces:interface/enabled" : "true",
               "@ietf-interfaces:interface/enabled" : {
                 "ietf-origin:origin" : "ietf-origin:learned"
               }
             }
          },
          {
            "edit-id" : "2",
            "operation" : "create",
            "target" : "/ietf-interfaces:interface=eth0/description",
            "value" : {
              "ietf-interface:interface/description" : "ip interface"
            }
          }
        ]
      }
    }
  }
}
Sample JSON Patch document 
PATCH /my/data HTTP/1.1
   Host: example.org
   Content-Length: 326
   Content-Type: application/json-patch+json
   If-Match: "abc123"

   [
     { "op": "test", "path": "/a/b/c", "value": "foo" },
     { "op": "remove", "path": "/a/b/c" },
     { "op": "add", "path": "/a/b/c", "value": [ "foo", "bar" ] },
     { "op": "replace", "path": "/a/b/c", "value": 42 },
     { "op": "move", "from": "/a/b/c", "path": "/a/b/d" },
     { "op": "copy", "from": "/a/b/d", "path": "/a/b/e" }
   ]
Proposed delta report format based on JSON patch format above 
[
  {
    "action": "ADD",
    "xpath": "/bookstore/categories/[@code=3]",
    "payload": {
      "code": 3,
      "name": "kidz"
    }
  },
  {
    "action": "DELETE",
    "xpath": "/bookstore/categories/[@code=1]",
    "payload": {
      "code": 1,
      "name": "Fiction"
    }
  },
  {
    "action": "UPDATE",
    "xpath": "/bookstore/categories/[@code=2]",
    "payload": {
      "name": "Comic"
    }

RFC 9144 example using RESTCONF

The YANG data model defines the <compare> operation as a new RPC. The operation takes the following input parameters:

  • source: the source or reference datastore
  • target: the datastore to be compared against the source datastore
  • filter-spec: a xpath based filter to specify the data nodes to be compared in a given datastore.  This allows a comparison operation to be applied only to a specific part of the datastore that is of interest, such as a particular subtree.
  • all: When set, this parameter indicates that all differences should be included, including differences pertaining to schema nodes that exist in only one of the datastores. When this parameter is not included, a prefiltering step is automatically applied to exclude data from the comparison that does not pertain to both datastores.
  • report-origin: this parameter is used to indicate whether to include origin or source data in delta report or not.

The operation provides the following output parameters:

  • differences: This parameter contains the list of differences. Those differences are encoded per the YANG Patch data model defined in [RFC8072]. 
Structure of ietf-nmda-compare. Source: RFC9144 
module: ietf-nmda-compare
  rpcs:
    +---x compare
       +---w input
       |  +---w source            identityref
       |  +---w target            identityref
       |  +---w all?              empty
       |  +---w report-origin?    empty
       |  +---w (filter-spec)?
       |     +--:(subtree-filter)
       |     |  +---w subtree-filter?
       |     +--:(xpath-filter)
       |        +---w xpath-filter?     yang:xpath1.0 {nc:xpath}?
       +--ro output
          +--ro (compare-response)?
             +--:(no-matches)
             |  +--ro no-matches?    empty
             +--:(differences)
                +--ro differences
                   +--ro yang-patch
                      +--ro patch-id    string
                      +--ro comment?    string
                      +--ro edit* [edit-id]
                         +--ro edit-id         string
                         +--ro operation       enumeration
                         +--ro target          target-resource-offset
                         +--ro point?          target-resource-offset
                         +--ro where?          enumeration
                         +--ro value?
                         +--ro source-value?

RESTCONF Example

Sample YANG Model

YANG Model 
container interfaces {
  description
    "Interface parameters.";
  list interface {
    key "name";
    leaf name {
      type string;
      description
        "The name of the interface.";
    }
    leaf description {
      type string;
      description
        "A textual description of the interface.";
    }
    leaf enabled {
      type boolean;
      default "true";
      description
        "This leaf contains the configured, desired state of the
         interface.";
    }
  }
}

Sample Data

Intended/Reference Data 
{
  "interfaces": {
    "interface": {
      "name": "eth0",
      "enabled": false,
      "description": "ip interface"
    }
  }
}
Operational/Comparand/Target Data 
{
  "interfaces": {
    "interface": {
      "name": "eth0",
      "enabled": true
    }
  }
}

Request in RESTCONF

POST Request 
POST /restconf/operations/ietf-nmda-compare:compare HTTP/1.1
Host: example.com
Content-Type: application/yang-data+json
Accept: application/yang-data+json

{ "ietf-nmda-compare:input" : {
   "source" : "ietf-datastores:operational",
   "target" : "ietf-datastores:intended",
   "report-origin" : null,
   "xpath-filter" : "/ietf-interfaces:interfaces"
   }
}

Response in RESTCONF

Response 
HTTP/1.1 200 OK
Date: Thu, 24 Jan 2019 20:56:30 GMT
Server: example-server
Content-Type: application/yang-data+json

{ "ietf-nmda-compare:output" : {
    "differences" : {
      "ietf-yang-patch:yang-patch" : {
        "patch-id" : "interface status",
        "comment" : "diff between intended (source) and operational",
        "edit" : [
          {
            "edit-id" : "1",
            "operation" : "replace",
            "target" : "/ietf-interfaces:interface=eth0/enabled",
            "value" : {
               "ietf-interfaces:interface/enabled" : "false"
            },
            "source-value" : {
               "ietf-interfaces:interface/enabled" : "true",
               "@ietf-interfaces:interface/enabled" : {
                 "ietf-origin:origin" : "ietf-origin:learned"
               }
             }
          },
          {
            "edit-id" : "2",
            "operation" : "create",
            "target" : "/ietf-interfaces:interface=eth0/description",
            "value" : {
              "ietf-interface:interface/description" : "ip interface"
            }
          }
        ]
      }
    }
  }
}
  • No labels