How Supervisor Solved No-IP DUC's IPv6 Update Issues

Managing dynamic DNS updates with the No-IP Dynamic Update Client (noip-duc) can sometimes be challenging, especially when integrating it with system-level service managers like systemd. In this case, a peculiar issue arose: while noip-duc worked perfectly fine when run manually, it failed to update IPv6 addresses when managed by systemd. After extensive troubleshooting, switching to Supervisor, a lightweight process manager, resolved the problem. Here’s a detailed account of the issue, the failed attempts at resolving it with systemd, and how Supervisor came to the rescue.

The Problem: A Systemd Mystery

The No-IP DUC is a simple yet powerful tool for keeping your dynamic DNS records updated. The setup seemed straightforward: configure a systemd service to run the client at boot and let it handle both IPv4 and IPv6 updates. However, things didn’t go as planned.When running noip-duc as a systemd service, it successfully updated the IPv4 address but failed to update the IPv6 address—even though the correct IP detection method (--ip-method https://ip1.dynupdate6.no-ip.com) was explicitly passed in the service configuration. Strangely, running the exact same command manually from the terminal worked flawlessly, updating both IPv4 and IPv6 addresses without any issues.The logs (journalctl) showed that the service was running and updating IPs. Yet, only the IPv4 address was being updated. This discrepancy hinted at subtle differences in how systemd and manual execution interacted with noip-duc.

https://www.noip.com/support/knowledgebase/running-linux-duc-v3-0-startup-2

Troubleshooting Systemd

To resolve the issue, several adjustments were made to the systemd service configuration:

1. Dependencies were modified to ensure that the service started only after network interfaces were fully initialized. For example, After=network-online.target was added to delay startup until the network was ready.
2. Retry mechanisms and restart behavior were adjusted to ensure that transient network issues wouldn’t cause failures.
3. All parameters were hardcoded in the service file to eliminate potential issues with environment variables or misconfigurations.

Despite these efforts, the problem persisted: IPv6 updates still failed when managed by systemd.

The Solution: Switching to Supervisor

With systemd proving unreliable for this specific use case, Supervisor was introduced as an alternative process manager. Unlike systemd, Supervisor provides a simpler execution environment that worked seamlessly with noip-duc.

Why Supervisor Worked

Supervisor resolved the issue because:

• It runs processes in an environment that appears more compatible with how noip-duc handles network interfaces.
• It offers robust logging and error handling features that made it easier to monitor and debug.
• It required minimal configuration changes beyond specifying the same command that worked manually.

Setting Up Supervisor

The transition to Supervisor was straightforward. After installing Supervisor (sudo apt install supervisor), a configuration file was created for noip-duc:

[program:noip-duc]
command=/usr/bin/noip-duc -g all.ddnskey.com --username your_username --password your_password --ip-method https://ip1.dynupdate6.no-ip.com/
autostart=true
autorestart=true
stderr_logfile=/var/log/noip-duc.err.log
stdout_logfile=/var/log/noip-duc.out.log
stdout_logfile_maxbytes=10MB
stderr_logfile_maxbytes=10MB
stdout_logfile_backups=5
stderr_logfile_backups=5        

After reloading Supervisor (sudo supervisorctl reread && sudo supervisorctl update) and starting the program (sudo supervisorctl start noip-duc), everything worked as expected. Both IPv4 and IPv6 addresses were updated successfully.

Key Observations About No-IP DUC

Logging Behavior

One key observation during this process was how noip-duc handles logging. Unlike most programs that write informational messages to standard output (stdout), noip-duc writes almost all its logs—including informational messages—to standard error (stderr). This behavior was consistent whether running manually or through a process manager.For example:

[2024-12-29T23:42:25Z INFO  noip_duc::observer] got new ip; current=2605:ad80:10:b8b5:5d97:7e90:c3d4:41f4, previous=0.0.0.0
[2024-12-29T23:42:26Z INFO  noip_duc::observer] update successful; current=2605:ad80:10:b8b5:5d97:7e90:c3d4:41f4, previous=0.0.0.0        

This behavior required careful attention when configuring logging in Supervisor. By explicitly redirecting both stderr and stdout to log files, all messages were captured reliably.

IPv6 Updates

Once managed by Supervisor, noip-duc updated IPv6 addresses without requiring additional tweaks beyond specifying the correct IP detection method (--ip-method https://ip1.dynupdate6.no-ip.com). This confirmed that the issue was not with noip-duc itself but rather with how it interacted with systemd.

Lessons Learned

This experience highlighted several important points:

1. Systemd and No-IP DUC Compatibility Issues: While systemd is powerful and widely used, it can sometimes face compatibility challenges with specific applications like noip-duc. In this case, the behavior of noip-duc under systemd led to issues with updating IPv6 addresses, despite correct configurations. This highlights that certain applications may require alternative process managers for optimal performance.
2. Supervisor Is a Great Alternative: For managing background processes like dynamic DNS clients, Supervisor offers simplicity and reliability.
3. Understand Logging Behavior: Knowing that noip-duc writes logs to stderr is crucial for effective monitoring and debugging.

Conclusion

Switching from systemd to Supervisor resolved the issue of No-IP DUC failing to update IPv6 addresses. The process manager’s simpler execution environment proved more compatible with noip-duc, making it an excellent choice for this use case.If you’re facing similar challenges with dynamic DNS clients or other background processes, consider using Supervisor as an alternative to systemd — it might save you hours of troubleshooting!