Bad Reqeust 400

[arnaudvre]

Hi there, I've followed the installation steps precisely but get a bad request 400.

OS: Ubuntu 24.04
Netbox: v4.4.2

Here's the output to the verification done at the end of each installation step:

postgresql

psql --username netbox --password --host localhost netbox
Password: 
psql (16.10 (Ubuntu 16.10-0ubuntu0.24.04.1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, compression: off)
Type "help" for help.

netbox=> \conninfo
You are connected to database "netbox" as user "netbox" on host "localhost" (address "127.0.0.1") at port "5432".
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, compression: off)
netbox=> \q

Reddis

redis-cli ping
PONG

Netbox

python3 manage.py runserver 0.0.0.0:8000 --insecure
Performing system checks...

System check identified no issues (0 silenced).
October 09, 2025 - 14:55:23
Django version 5.2.6, using settings 'netbox.settings'
Starting development server at http://0.0.0.0:8000/
Quit the server with CONTROL-C.

Gunicorn

systemctl status netbox.service
● netbox.service - NetBox WSGI Service
     Loaded: loaded (/etc/systemd/system/netbox.service; enabled; preset: enabled)
     Active: active (running) since Thu 2025-10-09 14:07:04 UTC; 49min ago
       Docs: https://docs.netbox.dev/
   Main PID: 1041 (gunicorn)
      Tasks: 9 (limit: 4605)
     Memory: 793.9M (peak: 794.4M)
        CPU: 18.212s
     CGroup: /system.slice/netbox.service
             ├─1041 /opt/netbox/venv/bin/python3 /opt/netbox/venv/bin/gunicorn --pid /var/tmp/netbox.pid --pythonpath /opt/netbox/netbox --config /opt/netbox/gunicorn.py netbox.wsgi
             ├─1080 /opt/netbox/venv/bin/python3 /opt/netbox/venv/bin/gunicorn --pid /var/tmp/netbox.pid --pythonpath /opt/netbox/netbox --config /opt/netbox/gunicorn.py netbox.wsgi
             ├─1081 /opt/netbox/venv/bin/python3 /opt/netbox/venv/bin/gunicorn --pid /var/tmp/netbox.pid --pythonpath /opt/netbox/netbox --config /opt/netbox/gunicorn.py netbox.wsgi
             ├─1088 /opt/netbox/venv/bin/python3 /opt/netbox/venv/bin/gunicorn --pid /var/tmp/netbox.pid --pythonpath /opt/netbox/netbox --config /opt/netbox/gunicorn.py netbox.wsgi
             ├─1090 /opt/netbox/venv/bin/python3 /opt/netbox/venv/bin/gunicorn --pid /var/tmp/netbox.pid --pythonpath /opt/netbox/netbox --config /opt/netbox/gunicorn.py netbox.wsgi
             └─1091 /opt/netbox/venv/bin/python3 /opt/netbox/venv/bin/gunicorn --pid /var/tmp/netbox.pid --pythonpath /opt/netbox/netbox --config /opt/netbox/gunicorn.py netbox.wsgi

Oct 09 14:07:04 netboxdemo systemd[1]: Started netbox.service - NetBox WSGI Service.
Oct 09 14:07:04 netboxdemo gunicorn[1041]: [2025-10-09 14:07:04 +0000] [1041] [INFO] Starting gunicorn 23.0.0
Oct 09 14:07:04 netboxdemo gunicorn[1041]: [2025-10-09 14:07:04 +0000] [1041] [INFO] Listening at: http://127.0.0.1:8001 (1041)
Oct 09 14:07:04 netboxdemo gunicorn[1041]: [2025-10-09 14:07:04 +0000] [1041] [INFO] Using worker: gthread
Oct 09 14:07:04 netboxdemo gunicorn[1080]: [2025-10-09 14:07:04 +0000] [1080] [INFO] Booting worker with pid: 1080
Oct 09 14:07:04 netboxdemo gunicorn[1081]: [2025-10-09 14:07:04 +0000] [1081] [INFO] Booting worker with pid: 1081
Oct 09 14:07:04 netboxdemo gunicorn[1088]: [2025-10-09 14:07:04 +0000] [1088] [INFO] Booting worker with pid: 1088
Oct 09 14:07:04 netboxdemo gunicorn[1090]: [2025-10-09 14:07:04 +0000] [1090] [INFO] Booting worker with pid: 1090
Oct 09 14:07:04 netboxdemo gunicorn[1091]: [2025-10-09 14:07:04 +0000] [1091] [INFO] Booting worker with pid: 1091

And finally the error with HTTP:

I've tried enabling info level logging in Nginx but the error log doesn't show much:

[arnaudvre]

Interestingly I don't get the error when accessing the main page using the IP rather than the hostname even though the IP resolves correctly....

Tried changing nginx sites_availble server_name to the fqdn of the server rather than it's IP and restarted netbox, netbox-rq and nginx but same error.

[markkuleinio]

I'd recommend reading the link provided by @pheus above, and changing ALLOWED_HOSTS accordingly.

[arnaudvre]

I've re-deployed Ubuntu 24.04 with no customizations, only configuring IP info and a user, to rule out the possibility of something weird with the innocent looking changes applied during a normal deployment. Still the same error. I've searched for a setting in the nginx configuration that could cause this but nothing stands out.

[arnaudvre]

Unfortunately changing the allowed hosts doesn't work, I know for 100% certain that the configuration worked fine previously with only the IP in ALLOWED_HOSTS but here I've tried = ['*'] as well as = ['ip_address', 'hostname'] and then = ['ip_address', 'fqdn'] each time rebooting the VM to leave nothing to chance and still error 400 on hostname only.

[arnaudvre]

Forward and reverse name lookups are working and the output of the hostname command as well as hostname -i and hostname -f are correct.

[pheus]

Hi there! Just to clarify what @markkuleinio and I meant:

In your NetBox configuration.py, ensure the ALLOWED_HOSTS setting includes every hostname and IP address you’ll use to access the app (as described in the NetBox installation docs). If something is missing, Django will block the request.

Example:

ALLOWED_HOSTS = [
    "netbox.example.com",
    "203.0.113.15",
    "localhost",
    "127.0.0.1",
]

If you’re behind a proxy or load balancer, also include the hostname/IP that NetBox actually sees. After updating the setting, restart the NetBox service.

If you’ve already done this and still run into issues, please share the exact error message and your current ALLOWED_HOSTS (feel free to redact sensitive details), and we’ll help you troubleshoot further.

[pheus]

Quick check — have you updated your NetBox configuration to match the latest example?
In recent releases, the database settings format has changed. Here’s the current template to use and adapt:

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",  # Database engine
        "NAME": "netbox",        # Database name
        "USER": "",              # PostgreSQL username
        "PASSWORD": "",          # PostgreSQL password
        "HOST": "localhost",     # Database server (hostname or IP)
        "PORT": "",              # Database port (leave blank for default)
        "CONN_MAX_AGE": 300,     # Max database connection age (seconds)
    }
}

[arnaudvre]

Also tcpdump shows no weirdness in https communication but just for good measure I've also turned off the VM to confirm that there's no duplicate IP

[arnaudvre]

Unfortunately still the same error setup like this:

[arnaudvre]

When the VM first came up from the reboot the error was the same but refreshing the page later on brought it up! For completeness I reverted the ALLOWED_HOSTS to only the IP to narrow down which setting exactly is causing the issue and after a reboot it's back to the error again so I went back to the complete list of ALLOWED_HOSTS and rebooted and now again the error so waiting to see if refreshing after a while will bring back the page. netbox, netbox-rq and nginx all look happy according the systemct status though. So far have tried every few minutes for 15 minutes and still the error.

[arnaudvre]

I've destroyed and redeployed the VM with the settings above which worked once previously but still the bad request with hostname, I can login to the UI via the IP no hassle and everything looks normal.

[arnaudvre]

after logging in via the GUI using the IP, I went back to https://fqdn and it's working now.....