ZeroTier has been a reliable solution for establishing VPN connections between devices, even when they are located behind NAT. However, after installing ZeroTier on my brother’s Raspberry Pi home server, I encountered a baffling issue: it would work fine for the first hour or so, and then lose connection from outside. The only way to re-establish the connection was to reboot the Raspberry Pi.

This problem was further compounded by the fact that if I had an ongoing file copy operation, I could still connect to the Raspberry Pi from the specific machine involved in the transfer. But if I switched to another device, like my laptop, I couldn’t connect at all. The sudo zerotier-cli info command showed the status as “OFFLINE.”

The Investigation: Searching for the Root Cause

After scouring the internet for answers and receiving advice from fellow Redditors, I opted for a workaround instead of pinpointing the root cause. This involved creating a script that checks ZeroTier’s status periodically and restarts the service if it’s offline.

Here’s the script I used (check_zerotier.sh):

#!/bin/bash

# Check if the response from "zerotier-cli status" contains "OFFLINE"
status=$(/var/lib/zerotier-one/zerotier-cli status)

if [[ $status == *"OFFLINE"* ]]; then
    echo "OFFLINE! Restarting zerotier-one"
    # If it does contain "OFFLINE", restart zerotier with the command "service zerotier-one restart"
    /usr/sbin/service zerotier-one restart
fi

if [[ $status == *"ONLINE"* ]]; then
    echo "ONLINE! Doing nothing"
fi

To automate the process, I added an entry in the crontab file to run the script every 10 minutes:

*/10 * * * * /usr/scripts/check_zerotier.sh 2>&1 | /usr/scripts/formatLog.sh 2>&1 >> /var/log/zt_check.log 2>&1

I also created a formatLog.sh script to format the log output:

#!/bin/bash

while read line; do
  current_time=$(date +"[%Y-%m-%d %H:%M:%S]")
  echo "$current_time $line"
done

The Workaround: A Reliable Solution

By implementing this workaround, I managed to bypass the issue and ensure that ZeroTier remains functional on my brother’s Raspberry Pi home server. While I didn’t identify the root cause of the problem, this solution has been effective in keeping the connection stable and preventing any disruptions.

Conclusion

Sometimes, finding the root cause of an issue can be like searching for a needle in a haystack. In cases like these, it’s essential to focus on finding a reliable workaround that can keep things running smoothly. In my case, a simple script and a cron job were enough to prevent ZeroTier from going offline and maintain a stable connection. I never pinned down the underlying cause (and at the time I cared more about keeping the box reachable than doing deep archaeology), but this watchdog approach kept the connection stable.