Expose a service on the Fly 6PN so other Machines can reach it (fly-local-6pn binding)
domain: fly.io · 4 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
In your app, bind the listener to `fly-local-6pn` (aliased in /etc/hosts to the Machine's current 6PN address) instead of 127.0.0.1 or 0.0.0.0, e.g. server.listen('fly-local-6pn:8080').
Build and deploy: `fly deploy -a <app>`.
Other Machines in the same org and WireGuard-connected devices can now reach it at `<appname>.internal:8080`, or a specific machine at `<machine_id>.vm.<app>.internal:8080`.
To use the actual numeric 6PN address at runtime, read the `FLY_PRIVATE_IP` environment variable on startup.
Known gotchas
Binding only to 127.0.0.1 makes the service unreachable over the 6PN - you MUST bind to `fly-local-6pn` (or the 6PN address) for inter-Machine traffic.
6PN connectivity bypasses Fly Proxy, so autostop/autostart are NOT triggered for these endpoints. Allocate a Flycast address (shared IP) if you need Fly Proxy features on an internal service.
6PN addresses are not static; re-read FLY_PRIVATE_IP on every boot because the address can change after a migration/reboot.
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