Waiting on Tailscale
I restarted my server the other day, and I realized one of my systemd services failed to start on boot because the Tailscale IP address was not assignable:
# journalctl -u bad-bad-not-good.service
...
listen tcp 100.11.22.33:8080: bind: cannot assign requested address
This is easy enough to fix. The service should wait to start until after Tailscale is online, so let’s just add
tailscaled.service to the the service’s wants and after properties, reboot, and…
# journalctl -u bad-bad-not-good.service
...
listen tcp 100.11.22.33:8080: bind: cannot assign requested address
Huh. It turns out Tailscale comes up a bit before its IP address is available. I was tempted to add an ExecStartPre
to my service to sleep for 1 second – gross! – but eventually I found systemd’s fabulous
systemd-networkd-wait-online command, which exits when a given interface has an IP
address. Call it with -i [interface name] and either -4 or -6 to wait for an IPv4 or IPv6 address.
Wrapping it up into a service gives you something like this:
# tailscale-online.service
[Unit]
Description=Wait for Tailscale to have an IPv4 address
Requisite=systemd-networkd.service
After=systemd-networkd.service
Conflicts=shutdown.target
[Service]
ExecStart=/usr/lib/systemd/systemd-networkd-wait-online -i tailscale0 -4
RemainAfterExit=true
Type=oneshot
Services using your Tailscale IP address can now depend on tailscale-online.