systemd-resolved is not used, but resolvconf, which should be fine. openresolv is an alternative to resolvconf with more feature, but it sometimes has strange implications like restarting known local DNS resolvers whenever a new IPv6 RA is received, hence the features cause issues but nothing useful I’m aware of 
. Hence, I’d just leave it as it is.
Generally use journalctl -u wg-quick@Dietpi to debug issues with the WireGuard connection.
Hi, MichaIng thanks for answer. Yesterday I turn off and on my Rpi and VPN works OK. I will check that command when it stops working.
Regards.
No it stop working after reboot.
Linux DietPi 5.10.63-v7+
─────────────────────────────────────────────────────
DietPi v7.7.3 : 17:18 - Thu 11/11/21
─────────────────────────────────────────────────────
- Device model : RPi 3 Model B+ (armv7l)
- CPU temp : 34'C : 93'F (Cool runnings)
- LAN IP : 192.168.0.30 (eth0)
curl: (28) Resolving timed out after 3000 milliseconds
dietpi@DietPi:~$ sudo journalctl -u wg-quick@Dietpi
-- Logs begin at Thu 2021-11-11 17:17:02 CET, end at Thu 2021-11-11 17:19:06 CET. --
Nov 11 17:17:07 DietPi systemd[1]: Starting WireGuard via wg-quick(8) for Dietpi...
Nov 11 17:17:07 DietPi wg-quick[383]: [#] ip link add Dietpi type wireguard
Nov 11 17:17:08 DietPi wg-quick[383]: [#] wg setconf Dietpi /dev/fd/63
Nov 11 17:17:08 DietPi wg-quick[383]: [#] ip -4 address add 10.66.66.3/32 dev Dietpi
Nov 11 17:17:08 DietPi wg-quick[383]: [#] ip -6 address add fd42:42:42::3/128 dev Dietpi
Nov 11 17:17:08 DietPi wg-quick[383]: [#] ip link set mtu 1420 up dev Dietpi
Nov 11 17:17:08 DietPi wg-quick[383]: [#] resolvconf -a tun.Dietpi -m 0 -x
Nov 11 17:17:08 DietPi wg-quick[383]: Too few arguments.
Nov 11 17:17:08 DietPi wg-quick[383]: Too few arguments.
Nov 11 17:17:08 DietPi wg-quick[383]: [#] wg set Dietpi fwmark 51820
Nov 11 17:17:08 DietPi wg-quick[383]: [#] ip -6 route add ::/0 dev Dietpi table 51820
Nov 11 17:17:08 DietPi wg-quick[383]: [#] ip -6 rule add not fwmark 51820 table 51820
Nov 11 17:17:08 DietPi wg-quick[383]: [#] ip -6 rule add table main suppress_prefixlength 0
Nov 11 17:17:09 DietPi wg-quick[383]: [#] ip6tables-restore -n
Nov 11 17:17:09 DietPi wg-quick[383]: [#] ip -4 route add 0.0.0.0/0 dev Dietpi table 51820
Nov 11 17:17:09 DietPi wg-quick[383]: [#] ip -4 rule add not fwmark 51820 table 51820
Nov 11 17:17:09 DietPi wg-quick[383]: [#] ip -4 rule add table main suppress_prefixlength 0
Nov 11 17:17:09 DietPi wg-quick[383]: [#] sysctl -q net.ipv4.conf.all.src_valid_mark=1
Nov 11 17:17:09 DietPi wg-quick[383]: [#] iptables-restore -n
Nov 11 17:17:09 DietPi systemd[1]: Started WireGuard via wg-quick(8) for Dietpi.
dietpi@DietPi:~$
Regards.
and what is the status of the service?
dietpi@DietPi:~$ sudo systemctl status wg-quick@Dietpi
● wg-quick@Dietpi.service - WireGuard via wg-quick(8) for Di
etpi
Loaded: loaded (/lib/systemd/system/wg-quick@.service; enabled; vendor preset: enabled)
Active: active (exited) since Thu 2021-11-11 17:17:05 CET
; 2min 9s ago
Docs: man:wg-quick(8)
man:wg(8)
https://www.wireguard.com/
https://www.wireguard.com/quickstart/
https://git.zx2c4.com/wireguard-tools/about/src/man/wg-quick.8
https://git.zx2c4.com/wireguard-tools/about/src/man/wg.8
Process: 379 ExecStart=/usr/bin/wg-quick up Dietpi (code=exited, status=0/SUCCESS)
Main PID: 379 (code=exited, status=0/SUCCESS)
Nov 11 17:17:05 DietPi wg-quick[379]: [#] ip -6 route add ::/0 dev Dietpi table 51820
Nov 11 17:17:05 DietPi wg-quick[379]: [#] ip -6 rule add not fwmark 51820 table 51820
Nov 11 17:17:05 DietPi wg-quick[379]: [#] ip -6 rule add table main suppress_prefixlength 0
Nov 11 17:17:05 DietPi wg-quick[379]: [#] ip6tables-restore -n
Nov 11 17:17:05 DietPi wg-quick[379]: [#] ip -4 route add 0.0.0.0/0 dev Dietpi table 51820
Nov 11 17:17:05 DietPi wg-quick[379]: [#] ip -4 rule add not fwmark 51820 table 51820
Nov 11 17:17:05 DietPi wg-quick[379]: [#] ip -4 rule add table main suppress_prefixlength 0
Nov 11 17:17:05 DietPi wg-quick[379]: [#] sysctl -q net.ipv4.conf.all.src_valid_mark=1
Nov 11 17:17:05 DietPi wg-quick[379]: [#] iptables-restore -n
Nov 11 17:17:05 DietPi systemd[1]: Started WireGuard via wg-quick(8) for Dietpi.
dietpi@DietPi:~$
and
dietpi@DietPi:~$ ping google.com
ping: google.com: Temporary failure in name resolution
dietpi@DietPi:~$
you could activate Wireguard debug logging
https://gist.github.com/artizirk/5bc87e345f850a8a0724929e0436ef84
Hi, everything was fine until today I start actions in my Radarr panel. I refresh all indexers. Then my Dietpi stops again. I cannot connect with ssh and I must plug off from power supply. I noticed that when I don’t use services on my Dietpi VPN tunnel works OK. I can connect and makes upgrades and other stuff.
Hi Joulinar I’m back with the same problem. After last post on that thread I install transmission and Kodi on Rpi4. I stop using that Rpi3. I install wireguard client and use it only for that Rpi4. Everything works great but today I just make a dietpi-backup and reinstall 31 (Kodi). Now I noticed that my issue from Rpi3 is now on Rpi4 
DietPi v7.8.2 : 20:18 - Sun 12/05/21
─────────────────────────────────────────────────────
- Device model : RPi 4 Model B (aarch64)
- CPU temp : 44'C : 111'F (Optimal temperature)
- LAN IP : 192.168.0.31 (eth0)
curl: (28) Resolving timed out after 3001 milliseconds
Regards.
did you tried to restart wireguard service?
Yes, I reboot two times but I’m afraid that issue will occur next days also like on my rpi3. I don’t know how to diagnose that problem.
did you aktive debug logging as stated above?
Joulinar I try but don’t work:
dietpi@DietPi:~$ echo 'module wireguard +p' | sudo tee /sys/kernel/debug/dynamic_debug/control
tee: /sys/kernel/debug/dynamic_debug/control: No such file or directory
module wireguard +p
I go to documentation but there’s no easy explanation how to do that. I really don’t understant it.
Regards.
ahh dammit, the kernel module CONFIG_DYNAMIC_DEBUG is not enabled on RPI by default.
https://github.com/raspberrypi/linux/issues/3486
This would require the kernel to be rebuild/compiled by yourself. Not sure if it’s worth it.
OK, thanks. I noticed that happen when I start many downloads. Maybe I’ll limit the number of downloading and that will help.
regards.