After changing Rack to use "too small" RackType, not able to change RackType again, remove it, or make other edits to Rack

[ZPrimed]

Deployment Type

Self-hosted

Triage priority

N/A

NetBox Version

v4.1.11

Python Version

3.10

Steps to Reproduce

[steps edited after initial issue creation, but should be correct as of 2025-01-14]

1. Create a Rack of any number of U (let's use 42 as it's the default), name it "FooRack"
2. Create a RackType that is smaller than the Rack you initially created - say 16U, name it "TestRT-16U"
3. [edit: missing from original report] Add a Device to FooRack in a U / position that is "beyond the bounds" of TestRT-16U; e.g. put the Device at U17, or U20, or U42
4. Create another RackType that is the same number of U as the original Rack - 42U, name it "TestRT-42U"
5. Edit FooRack, and set the RackType to be TestRT-16U, and Save [this will complete successfully, but probably shouldn't, as TestRT-16U has fewer rack units than FooRack originally did!]
6. Now, edit FooRack again, and either try to set the RackType to "TestRT-42U", or hit the X next to the RackType in order to try to clear it entirely, and click Save. This will throw an error. In fact, even unrelated changes (like editing the Comments) will throw the same error.

Note: if you FIRST change the Rack to a RackType that has sufficient U for the Rack, this works correctly and will allow you to remove the RackType or change it again on a subsequent save. You only get the error if you choose the wrong-size RackType and save it during step 4.

Expected Behavior

1. I would prefer that the UI prevent me from self-harm, by warning or erroring that the RackType I was trying to switch my Rack to has fewer U than the existing Rack object I was changing, but this is just a wish/hope
2. Regardless of 1, the UI should allow me to change the RackType or remove it entirely from a Rack, without throwing errors

Observed Behavior

I receive an error message and am not able to save the changes made to the Rack object:

<class 'ValueError'>

'RackForm' has no field named 'u_height'.

Python version: 3.10.12
NetBox version: 4.1.11
Plugins: 
  netbox_topology_views: 4.1.0

I can reproduce this on the Public Demo instance, same error message other than the differing version numbers & plugins:

<class 'ValueError'>

'RackForm' has no field named 'u_height'.

Python version: 3.10.14
NetBox version: 4.2.0
Plugins: 
  netbox_demo: 0.5.0

[bctiemann]

@ZPrimed I've been trying to reproduce this under NetBox v4.2 without success. I've been creating 42U racks with no RackType, setting them to TestRT-16U (at which point they assume the height of the RackType, e.g. 16U), and then setting them to TestRT-42U or clearing the RackType entirely. All operations complete successfully (and clearing the RackType leaves the Rack with the height last inherited from the RackType it had).

Are you able to try this in NetBox v4.2? Or does the Rack need to have Devices assigned to it before this breaks?

[ZPrimed]

@bctiemann I apologize, I did leave out the crucial portion that the rack needs to have at least one device added to it. I was testing against the demo instance and just grabbed some existing demo rack (which already had one or more devices in it) which is why I didn't think to include that in my steps. 🤦 Sorry!

I'm unsure if the actual position of the racked device matters (i.e. does it need to be racked in a U that doesn't exist after selecting the too-small RackType), but I can try a bit more testing later today and will update here.

[bctiemann]

Verified that the described crash does happen as long as the racked devices are at elevations above what the smaller rack can support, i.e. U30 on a 16U rack.

Also note that the SVG rendering call to /api/dcim/racks/43/elevation/ fails when the smaller rack is selected:

Internal Server Error: /api/dcim/racks/43/elevation/
Traceback (most recent call last):
...
  File "/Users/btman/Development/netbox-community/netbox/netbox/dcim/api/views.py", line 210, in elevation
    drawing = rack.get_elevation_svg(
              ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/btman/Development/netbox-community/netbox/netbox/dcim/models/racks.py", line 588, in get_elevation_svg
    return elevation.render(face)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/btman/Development/netbox-community/netbox/netbox/dcim/svg/racks.py", line 342, in render
    self.draw_face(face)
  File "/Users/btman/Development/netbox-community/netbox/netbox/dcim/svg/racks.py", line 305, in draw_face
    for unit in self.rack.get_rack_units(face=face, expand_devices=False):
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/btman/Development/netbox-community/netbox/netbox/dcim/models/racks.py", line 494, in get_rack_units
    elevation[device.position]['device'] = device
    ~~~~~~~~~^^^^^^^^^^^^^^^^^
KeyError: Decimal('30.0')