Using Subdomains to Isolate Routing Campaigns

Use stable, non-sensitive labels that distinguish environment or campaign family without embedding short-lived creative names. Document reserved names and avoid collisions with application, email, or administrative hosts.

Map each subdomain to a clear flow scope, destinations, source policy, and owner. When several campaigns share a host, use path prefixes only with explicit precedence and unknown-path behavior.

Add the precise record required by the deployment, verify authoritative resolution, and confirm HTTPS before sending traffic. Wildcard certificates or DNS records simplify some estates but can widen the impact of a mistake.

Track active links and DNS dependencies before repointing or removing a hostname. A retired campaign can still receive late clicks, so select a safe response and retention period instead of immediately assigning the name elsewhere.

Send known visits to the new subdomain, a neighboring campaign host, an unknown path, and both destinations. A change intended for one host must not alter event attribution or responses on the others.