Server-side tracking is most effective when your tracking requests come from your own domain instead of a shared one, since this is what keeps your first-party cookies genuinely first-party.
Adding a domain
From your container's dashboard, add the subdomain you want to track from, for example track.yourdomain.com. You'll be given a CNAME target to add at your DNS provider.
Create a CNAME record for your chosen subdomain pointing at the target FlyNode gives you.
Wait for DNS to propagate - FlyNode checks this automatically and only attaches the domain once it verifies correctly.
Once verified, an SSL certificate is issued automatically and your container starts responding on that domain.
Why this matters for Preview mode
Adding your first custom tracking domain is also the moment FlyNode provisions a dedicated Preview Server for your container (see "Single vs. Dual Container Setup") - a real first-party domain is exactly the case a separate preview environment matters most for.
Still stuck?
Open a support ticket from your dashboard and include the container name.