systemd timer for ddns/dyndns/dynamic dns or any other http request

ddns.service

# /etc/systemd/system/ddns.service
[Unit]
Description=Updates ddns via curl

[Service]
Type=oneshot
ExecStart=/usr/bin/curl "https://your request goes here"
#You might have or want to change user/group
#User=nobody
#Group=nogroup
#Or just use a dynamically generated one
DynamicUser=yes

PrivateTmp=yes
ProtectSystem=strict
ProtectHome=true
MemoryDenyWriteExecute=yes
PrivateDevices=true
PrivateUsers=true
ProtectKernelTunables=true
ProtectKernelModules=true
ProtectControlGroups=true
RestrictNamespaces=true
LockPersonality=true
RestrictRealtime=true

[Install]
WantedBy=multi-user.target

ddns.timer

# /etc/systemd/system/ddns.timer
# systemctl enable ddns.timer
# systemctl start ddns.timer
[Unit]
Description=Update a ddns provider

[Timer]
OnBootSec=1s
OnUnitActiveSec=30s

[Install]
WantedBy=timers.target

For a scenario like this, you might simply want to use DynamicUser=yes instead of User=/Group= (requires >=systemd-232).

Added!