[BUG] dcd module: dcd_config.connector.creation_rules.host_attributes should not be null by default

[relrod]

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Where possible also test if the latest release and main branch are affected too. Complete all sections as described!

Describe the bug

    - name: Create DCD connection
      checkmk.general.dcd:
        dcd_config:
          dcd_id: homelab-kube
          title: kube.home.elrod.me
          connector:
            connector_type: piggyback
            creation_rules:
              - folder_path: /homelab
                delete_hosts: false
            restrict_source_hosts:
              - kube.home.elrod.me

leads to:

[ERROR]: Task failed: Module failed: 400 - Bad request: Parameter or validation failure Details: b'{"title": "Bad Request", "status": 400, "detail": "These fields have problems: connector", "fields": {"connector": {"creation_rules": {"0": {"host_attributes": ["Field may not be null."]}}}}}'

But if I add host_attributes: {} to the creation rule, it works.

Component Name

Write the short name of the module or plugin below, use your best guess if unsure. Keeping the below syntax helps us match the issues to labels.

Component Name: dcd

[robin-checkmk]

@lgetwan from what I can see, the option host_attributes is documented as "optional", so the behavior described above is clearly a bug. The REST API does seem to consider it an optional parameter as well, so I think we need to either update our documentation or change the code to omit it.
From a non-dev perspective I could see why both approaches could be reasonable. It might have a surprising effect, if defaults are used instead of what a user specifies explicitly. On the other hand is it rather convenient to not having to specify host_attributes.
What do you think?

[lgetwan]

Strange!
When using the Swagger UI, it needs the host_attributes, as well:

{
  "title": "My fancy dynamic host configuration",
  "site": "klapplg",
  "dcd_id": "MyDcd01",
  "connector": {
    "connector_type": "piggyback",
    "creation_rules": [
      {
        "folder_path": "/",
        "host_attributes": {}
      }
    ]
  }
}

Not sending the empty dict, leads to an Internal Server Error:

{
  "title": "My fancy dynamic host configuration",
  "site": "klapplg",
  "dcd_id": "MyDcd02",
  "connector": {
    "connector_type": "piggyback",
    "creation_rules": [
      {
        "folder_path": "/"
      }
    ]
  }
}

==>

{
  "title": "Internal Server Error",
  "status": 500,
  "detail": "KeyError: 'host_attributes'. Crash report generated. Please submit.",
  "ext": {
    "id": "ceb51720-00e7-11f1-8a91-000ec6645d6d",
    "crash_type": "rest_api",
    "exc_type": "KeyError",
    "exc_value": "'host_attributes'",
    "local_vars": "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",
    "details": {
      "crash_report_url": {
        "href": "https://localhost/klapplg/check_mk/crash.py?crash_id=ceb51720-00e7-11f1-8a91-000ec6645d6d&site=klapplg",
        "method": "get",
        "rel": "cmk/crash-report",
        "type": "text/html"
      },
      "request_info": {
        "method": "POST",
        "data_received": {
          "title": "My fancy dynamic host configuration",
          "site": "klapplg",
          "dcd_id": "MyDcd02",
          "connector": {
            "connector_type": "piggyback",
            "creation_rules": [
              {
                "folder_path": "/"
              }
            ]
          }
        },
        "headers": {
          "accept": "application/json",
          "content_type": "application/json"
        }
      },
      "check_mk_info": {
        "site": "klapplg",
        "check_mk_user": {
          "user_id": "cmkadmin",
          "user_roles": [
            "admin"
          ],
          "authorized_sites": [
            "klapplg"
          ]
        }
      }
    },
    "core": "cmc",
    "python_version": "3.12.11 (main, Dec  7 2025, 01:06:50) [GCC 14.2.0]",
    "edition": "cce",
    "python_paths": [
      "/omd/sites/klapplg/local/lib/python3",
      "/omd/sites/klapplg/lib/python3/cloud",
      "/omd/sites/klapplg/lib/python312.zip",
      "/omd/sites/klapplg/lib/python3.12",
      "/omd/sites/klapplg/lib/python3.12/lib-dynload",
      "/omd/sites/klapplg/lib/python3.12/site-packages",
      "/omd/sites/klapplg/lib/python3"
    ],
    "version": "2.4.0p18",
    "time": "2026-02-03T11:05:03.061105",
    "os": "Ubuntu 24.04.3 LTS",
    "exc_traceback": [
      "Traceback (most recent call last):",
      "  File \"/omd/sites/klapplg/lib/python3/cmk/gui/wsgi/applications/rest_api.py\", line 509, in wsgi_app",
      "    return wsgi_endpoint(environ, start_response)",
      "           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^",
      "  File \"/omd/sites/klapplg/lib/python3/cmk/gui/wsgi/applications/utils.py\", line 48, in __call__",
      "    return self.wsgi_app(environ, start_response)",
      "           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^",
      "  File \"/omd/sites/klapplg/lib/python3/cmk/gui/wsgi/applications/rest_api.py\", line 180, in wsgi_app",
      "    wsgi_app = self.endpoint.wrapped(ParameterDict(path_args))",
      "               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^",
      "  File \"/omd/sites/klapplg/lib/python3/cmk/gui/openapi/restful_objects/decorators.py\", line 900, in _wrapper",
      "    response = func(param)",
      "               ^^^^^^^^^^^",
      "  File \"/omd/sites/klapplg/lib/python3/cmk/gui/openapi/restful_objects/decorators.py\", line 889, in _validating_wrapper",
      "    return self._validate_response(response_schema, _params)",
      "           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^",
      "  File \"/omd/sites/klapplg/lib/python3/cmk/gui/openapi/restful_objects/decorators.py\", line 684, in _validate_response",
      "    response = self.func(_params)",
      "               ^^^^^^^^^^^^^^^^^^",
      "  File \"/omd/sites/klapplg/lib/python3/cmk/gui/cee/dcd/_openapi/__init__.py\", line 113, in create_rule",
      "    internal_connector = _piggyback_request_schema_to_internal_record(connector)",
      "                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^",
      "  File \"/omd/sites/klapplg/lib/python3/cmk/gui/cee/dcd/_openapi/__init__.py\", line 259, in _piggyback_request_schema_to_internal_record",
      "    \"host_attributes\": [(field, value) for field, value in rule[\"host_attributes\"].items()],",
      "                                                           ~~~~^^^^^^^^^^^^^^^^^^^",
      "KeyError: 'host_attributes'",
      ""
    ]
  }
}

[lgetwan]

We could set the host_atteibutes to "{}" if they are not provided by the user.
But I'd prefer having the bug fixed in the REST API.

I opened an internal ticket.

[robin-checkmk]

Internal reference: CMK-29925