Reserved Domain or Dynamic Subdomain for Free-Tier Ngrok Tunnels

A developer integrating a client application with an Ngrok tunnel requires a stable endpoint URL that does not change between restarts, ensuring that webhooks or API calls remain valid.

Ngrok offers two approaches: a reserved domain (e.g., myapp.ngrok.io) that persists across restarts when linked to an authtoken, but is only available on paid plans or trial tiers; and a dynamic subdomain that provides a free, random URL on each start, which breaks any client configuration expecting a fixed address. Furthermore, Ngrok does not cache DNS responses, yet the local TCP proxy may retain stale connection state if a tunnel is reused without a full restart, potentially causing unexpected behavior regardless of the domain type chosen.

Given the free-tier limitation, can a reserved domain be emulated through alternative Ngrok features or external DNS without upgrading? How does the presence of stale TCP state from tunnel reuse affect reliability for both reserved and dynamic endpoints, and what mitigation strategies exist within Ngrok's current model?