In 3.5.0 image sync download-bootresourcefile activity fails with "integer division or modulo by zero"

[Jacopo Rota]

In 3.5.0 in an environment with 3 nodes in HA some "download-bootresourcefile" are always failing with

{
  "message": "integer division or modulo by zero",
  "stackTrace": " File \"/snap/maas/34137/usr/lib/python3/dist-packages/temporalio/worker/_activity.py\", line 439, in _run_activity\n result = await impl.execute_activity(input)\n\n File \"/snap/maas/34137/usr/lib/python3/dist-packages/temporalio/worker/_activity.py\", line 694, in execute_activity\n return await input.fn(*input.args)\n\n File \"/snap/maas/34137/lib/python3.10/site-packages/maasserver/workflow/bootresource.py\", line 123, in download_bootresourcefile\n activity.info().attempt % len(param.source_list)\n",
  "applicationFailureInfo": {
    "type": "ZeroDivisionError"
  }
}

see the screenshot attached.

This happens because the parameter of the bootresource-download activity is

[
  {
    "extract_paths": [],
    "force": false,
    "rfile_ids": [
      22
    ],
    "sha256": "189757828954b839863e877fada48e58a9f4d86ac4ff601ab84cceb8896a12b1",
    "size": 0,
    "source_list": [],
    "total_size": 133248031
  }
]

and source_list is empty

[Jacopo Rota (r00ta)]

Found out that

    @activity.defn(name="get-bootresourcefile-endpoints")
    async def get_bootresourcefile_endpoints(self) -> dict[str, list]:
        url = f"{self.url}/api/2.0/regioncontrollers/"
        regions = await self.request_async("GET", url)
        return {
            r["system_id"]: [
                compose_URL("http://:5240/MAAS/boot-resources/", src)
                for src in r["ip_addresses"]
            ]
            for r in regions
        }

might actually return empty list for some regions

[
  {
    "dnsatk": [],
    "m4mmw8": [
      "http://10.244.40.32:5240/MAAS/boot-resources/",
      "http://192.168.33.23:5240/MAAS/boot-resources/"
    ],
    "mthcpn": [
      "http://10.244.40.31:5240/MAAS/boot-resources/",
      "http://10.244.40.33:5240/MAAS/boot-resources/",
      "http://192.168.33.22:5240/MAAS/boot-resources/"
    ]
  }
]