Nova and Horizon: UTC Timestamp Translation Across Regional Time Zones

Answer to the Core Questions

1. Does Horizon let you switch between UTC and a Nova node’s regional time zone?

• Horizon’s UI does not expose a per‑instance or per‑region toggle. The conversion is always done from UTC to the user’s time zone, which can be set per‑session in Profile → Time Zone or globally in horizon.conf.
• Because Nova instances run on hosts that may have a different local clock, Horizon does not automatically align the UI to that host’s zone. If you need the host’s local time for audit purposes, you must consult the host logs directly.

2. Is the conversion logic standardized or browser‑dependent?

• Server‑side: Horizon uses Django’s TIME_ZONE and USE_TZ settings. When USE_TZ=True (the default), all datetime objects are timezone‑aware and converted to the user’s zone on the server before being sent to the browser.
• Client‑side: The browser’s JavaScript Intl.DateTimeFormat API performs the final formatting. If a browser lacks Intl support or JavaScript is disabled, Horizon falls back to displaying the raw UTC string.
• Thus the logic is standardized across OpenStack distributions, but the final display can be affected by the client environment.

Practical Steps for Your Scenario

1. Check Horizon configuration – Open /etc/openstack-dashboard/local_settings.py (or horizon.conf in newer releases). Verify:

   TIME_ZONE = 'UTC'
   USE_TZ = True
   

   If you want a server‑side default other than UTC, set TIME_ZONE accordingly.
2. Restart Horizon after any change:

   sudo systemctl restart openstack-dashboard.service
   

3. Verify server‑side awareness with a quick Python check on the Horizon host:

   python3 - <<'PY'
   from django.utils import timezone
   print(timezone.now().astimezone())
   PY
   

   The output should include the server’s local offset if TIME_ZONE is set.
4. Test per‑user setting – Log in as an admin, go to Profile → Time Zone, pick a zone (e.g., America/New_York), and confirm that timestamps on the dashboard shift accordingly.
5. Client‑side confirmation – Open the browser console, run:

   new Intl.DateTimeFormat('en-US', {timeZoneName:'short'}).format(new Date('2026-09-19T12:00:00Z'))
   

   The result should reflect the selected user zone.
6. Remember that audit logs stored by Nova remain in UTC. If you need to correlate Horizon UI times with host logs, convert the Horizon times back to UTC or use the host’s local time for both.

What to Check If Times Still Look Wrong

• Is the Horizon server’s system clock set to UTC? Run timedatectl status.
• Is the /etc/localtime link pointing to the correct zone database? Verify with ls -l /etc/localtime.
• Are reverse proxies stripping X‑Forwarded‑Proto or X‑Forwarded‑For headers? That can affect JavaScript loading and time‑zone scripts.
• Are you using an older Horizon version where USE_TZ was defaulted to False? Upgrade and re‑enable USE_TZ=True.

Once these items are confirmed, Horizon will correctly translate UTC timestamps to the chosen user time zone, and any discrepancy with Nova host logs will be due to the inherent difference between server and host clocks, not a Horizon bug.