Updating a Cable Termination over the API results in a missing connection/trace

[Hedius]

Deployment Type

Self-hosted

NetBox Version

v3.7.3

Python Version

3.11

Steps to Reproduce

I only was able to identify issue #14200, #14137 (closed/rejected) as a similar problem.

The following steps are made for a clean empty netbox installation.

Initial setup

1. Create a manufacturer (HPE in this case).

2. Create a device type for that one. (ProLiant DL360 Gen11 in this case).

3. Create a device/VM role (Server in this case).

4. Create a site (DC1).

5. Create 2 Servers with that role, site and type. (server001, server002).
   

6. Assign an interface (eth0 in this case) to both servers.

Create a cable between both

{
  "a_terminations": [
    {
      "object_type": "dcim.interface",
      "object_id": 1
    }
  ],
  "b_terminations": [
    {
      "object_type": "dcim.interface",
      "object_id": 2
    }
  ],
  "status": "connected"
}

curl -X 'POST' \
  'http://127.0.0.1:8000/api/dcim/cables/' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "a_terminations": [
    {
      "object_type": "dcim.interface",
      "object_id": 1
    }
  ],
  "b_terminations": [
    {
      "object_type": "dcim.interface",
      "object_id": 2
    }
  ],
  "status": "connected"
}'

After this POST the interfaces are cabled and you can see the connection and link peers. 2 Terminations with the IDs (1,2) exist after this.

Add more interfaces to servers and change the cable in the GUI.

1. Add eth1 to server002 (same config.
2. Change the B termination for the cable from eth0 to eth1.
   

The old termination is deleted, replaced with a new one, the connection is updated and you can trace the cable.

Now over the API, Delete termination B

1. There is a similar issue from december: Path Status "Not Reachable" after edit cable terminaison by API #14137 (got closed, though)
2. The person there updated the termination by patching the cable over api/dcim/cables.
3. Both the changelog screenshot from above and @jeremystretch ´s comment show that the correct way is to delete the termination and create a new one.
4. So delete the termination for cable 1 (server002 -> eth1) with a DELETE to /api/dcim/cable-terminations/3/
5. curl -X 'DELETE' 'http://127.0.0.1:8000/api/dcim/cable-terminations/3/'

Create a new B termination for server002 -> eth0

post data

{
  "cable": 1,
  "cable_end": "B",
  "termination_type": "dcim.interface",
  "termination_id": 2
}

curl -X 'POST' \
  'http://127.0.0.1:8000/api/dcim/cable-terminations/' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "cable": 1,
  "cable_end": "B",
  "termination_type": "dcim.interface",
  "termination_id": 2
}'

Cable and terminations have correct data (Skip this... issue after this one :) )

Data for both terminations and the cable looks correct.... nothing special.

{
    "count": 2,
    "next": null,
    "previous": null,
    "results": [
        {
            "id": 1,
            "url": "http://127.0.0.1:8000/api/dcim/cable-terminations/1/",
            "display": "Cable #1 to eth0",
            "cable": 1,
            "cable_end": "A",
            "termination_type": "dcim.interface",
            "termination_id": 1,
            "termination": {
                "id": 1,
                "url": "http://127.0.0.1:8000/api/dcim/interfaces/1/",
                "display": "eth0",
                "device": {
                    "id": 1,
                    "url": "http://127.0.0.1:8000/api/dcim/devices/1/",
                    "display": "server001",
                    "name": "server001"
                },
                "name": "eth0",
                "cable": 1,
                "_occupied": true
            },
            "created": "2024-03-09T18:12:52.063515Z",
            "last_updated": "2024-03-09T18:12:52.063527Z"
        },
        {
            "id": 4,
            "url": "http://127.0.0.1:8000/api/dcim/cable-terminations/4/",
            "display": "Cable #1 to eth0",
            "cable": 1,
            "cable_end": "B",
            "termination_type": "dcim.interface",
            "termination_id": 2,
            "termination": {
                "id": 2,
                "url": "http://127.0.0.1:8000/api/dcim/interfaces/2/",
                "display": "eth0",
                "device": {
                    "id": 2,
                    "url": "http://127.0.0.1:8000/api/dcim/devices/2/",
                    "display": "server002",
                    "name": "server002"
                },
                "name": "eth0",
                "cable": 1,
                "_occupied": true
            },
            "created": "2024-03-09T18:33:25.250711Z",
            "last_updated": "2024-03-09T18:33:25.250729Z"
        }
    ]
}

{
    "count": 1,
    "next": null,
    "previous": null,
    "results": [
        {
            "id": 1,
            "url": "http://127.0.0.1:8000/api/dcim/cables/1/",
            "display": "#1",
            "type": "",
            "a_terminations": [
                {
                    "object_type": "dcim.interface",
                    "object_id": 1,
                    "object": {
                        "id": 1,
                        "url": "http://127.0.0.1:8000/api/dcim/interfaces/1/",
                        "display": "eth0",
                        "device": {
                            "id": 1,
                            "url": "http://127.0.0.1:8000/api/dcim/devices/1/",
                            "display": "server001",
                            "name": "server001"
                        },
                        "name": "eth0",
                        "cable": 1,
                        "_occupied": true
                    }
                }
            ],
            "b_terminations": [
                {
                    "object_type": "dcim.interface",
                    "object_id": 2,
                    "object": {
                        "id": 2,
                        "url": "http://127.0.0.1:8000/api/dcim/interfaces/2/",
                        "display": "eth0",
                        "device": {
                            "id": 2,
                            "url": "http://127.0.0.1:8000/api/dcim/devices/2/",
                            "display": "server002",
                            "name": "server002"
                        },
                        "name": "eth0",
                        "cable": 1,
                        "_occupied": true
                    }
                }
            ],
            "status": {
                "value": "connected",
                "label": "Connected"
            },
            "tenant": null,
            "label": "",
            "color": "",
            "length": null,
            "length_unit": null,
            "description": "",
            "comments": "",
            "tags": [],
            "custom_fields": {},
            "created": "2024-03-09T18:12:52.049438Z",
            "last_updated": "2024-03-09T18:19:21.528022Z"
        }
    ]
}

Connection is missing

However, in the server -> interfaces view, the connection is not listed anymore.

And you can no longer trace the cable.

Tracing over the API is also not possible at this point.

Summary

Correct me if I did smth wrong... But GUI actions cause the same actions and you suggested in #14200 to do it like this. Is this the correct way for updating cables?

Expected Behavior

1. A cable should have a connection after deleting/creating its terminations over the API. (See the description from above.)

Observed Behavior

1. After deleting and creating a new termination for a cable, it does not have a connection anymore.
   Both terminations are interfaces. Furthermore, you cannot trace the path anymore.

[Hedius]

Correction, ignore the edit exception part. Duplicate to: #11460
Removed it from the report.

I actually meant to reference #14137 before.

[jeffgdotorg]

Thank you for opening a bug report and for taking the time to provide detailed steps to reproduce on a pristine system.

I was unable to reproduce the reported behavior on NetBox v3.7.4. Maybe this means we fixed the problem you're reporting in the course of doing other work. Please re-confirm the reported behavior on the current stable release and adjust your post above as necessary.

[Hedius]

Hi, thank you for your answer and for looking into it. I will redo my script on stable later this week.

[Hedius]

Hello I performed the same steps on NetBox 3.7,5 and I have the same issue again.

I took a cable. Deleted 1 termination over the API, created a new one and ended up with a cable without a connection as described above...

The cable exists with both terminations, but http://127.0.0.1:8000/dcim/interface-connections/ does not show any connections.

netbox=# select * from dcim_cable;
            created            |         last_updated         | custom_field_data | id | type |  status   | label | color | length | length_unit | _abs_length | tenant_id | comments | description 
-------------------------------+------------------------------+-------------------+----+------+-----------+-------+-------+--------+-------------+-------------+-----------+----------+-------------
 2024-04-06 20:05:42.600335+00 | 2024-04-06 20:05:42.60035+00 | {}                |  2 |      | connected |       |       |        |             |             |           |          | 

netbox=# select * from dcim_cabletermination;
 id | cable_end | termination_id | cable_id | termination_type_id | _device_id | _rack_id | _location_id | _site_id |            created            |         last_updated          
----+-----------+----------------+----------+---------------------+------------+----------+--------------+----------+-------------------------------+-------------------------------
  3 | A         |              1 |        2 |                  42 |          1 |          |              |        1 | 2024-04-06 20:05:42.622425+00 | 2024-04-06 20:05:42.622436+00
  5 | B         |              2 |        2 |                  42 |          3 |          |              |        1 | 2024-04-06 20:12:45.830316+00 | 2024-04-06 20:12:45.830331+00

netbox=# select * from dcim_cablepath;
 id |   _nodes    | is_active | is_split |           path           | is_complete 
----+-------------+-----------+----------+--------------------------+-------------
  3 | {42:1,29:2} | t         | f        | [["42:1"], ["29:2"], []] | f

The cable path only contains the A-Termination and the cable. The B-Termination is missing.

What I did is:

1. Create a cable with 2 terminations
2. Delete the B-Termination over the API
3. Create it again over the API ( as described above)

I looked at the signals of dcim for CablePaths and updates are triggered in different cases (dcim/signals.py):

1. If I create or update a cable (Editing a cable in the gui triggers this signal) (trace_path is the signa)
2. If I delete a termination or delete a cable.

So from that posting a cable termination to /api/cable-terminations will never trigger an update of a cable path. (Therefore, no path in the table.... Also verified that the logic does not get triggered with break points.)

Different take. (While in the referenced issue it was said that deleting/creating new cable terminations is the correct way, I gonna try now updating the cable directly with a PATCH to /api/dcim/cables/x/, because updating a termination cannot trigger the trace_path signal?

Before me changing the endpoints the path is documented correctly after creating the cable:

netbox=# select * from dcim_cablepath;
 id |      _nodes      | is_active | is_split |              path              | is_complete 
----+------------------+-----------+----------+--------------------------------+-------------
  9 | {42:1,29:3,42:2} | t         | f        | [["42:1"], ["29:3"], ["42:2"]] | t
 10 | {42:2,29:3,42:1} | t         | f        | [["42:2"], ["29:3"], ["42:1"]] | t

Updated cable the B termination of cable 3 from interface 2 to 3 with a PATCH to /api/dcim/cables/3/

Data:

{
  "b_terminations": [
    {
      "object_type": "dcim.interface",
      "object_id": 3
    }
  ]
}

This clearly seems to be incorrect though:

netbox=# select * from dcim_cablepath;
 id |        _nodes         | is_active | is_split |                  path                  | is_complete 
----+-----------------------+-----------+----------+----------------------------------------+-------------
  9 | {42:1,29:3}           | t         | f        | [["42:1"], ["29:3"], []]               | f
 11 | {42:1,29:3,42:3}      | t         | f        | [["42:1"], ["29:3"], ["42:3"]]         | t
 12 | {42:2,29:3,42:1,42:3} | t         | f        | [["42:2"], ["29:3"], ["42:1", "42:3"]] | t

It does update the terminations now and a Path from A to B is created.

The B-Termination is updated correctly, but old B-Termination shows now 2 paths. (Instead of the new one showing one only to the A-Temrination)

I am lost now...

@jeffgdotorg Can you please explain how you updated the termination over the API? Did you update the cable or did you delete/create the terminations?

[Hedius]

For reference: https://github.com/netbox-community/netbox/blob/develop/netbox/dcim/signals.py#L75 is the cable path logic, but I can only see it getting triggered if you use /api/dcim/cables

Jeremy made clear that you should not do this: #14137 (comment)

But posting a termination cannot trigger the trace_path logic. It is only triggered at

netbox/netbox/dcim/models/cables.py

Line 240 in b7668fb

trace_paths.send(Cable, instance=self, created=_created)

(cable modifications)

Correct me please if I am wrong here.
I have had the idea to open a PR and insert sending the trace_path signal in the cable termination save method, but this seems incorrect, because then trace paths would be triggered several times per cable modification/creation