Fly Dev Tunnel
Developers commonly use apps like ngrok, localtunnel, or cloudflared to expose a local web service at a publicly-accessible URL. This is useful for developing with HTTPS or sharing a site preview with a colleague or client.
By utilizing Fly, WireGuard, and a reverse proxy, you can achieve something similar with the added benefits of a custom domain and subdomains mapped to specific ports. Best of all, it’s free as long as you stay within Fly’s generous limits.
1. Install flyctl, the Fly command-line utility
Follow the instructions for your OS. After installation, run
flyctl auth login to sign up or sign in.
2. Connect to Fly via WireGuard
Install WireGuard for your OS. Next, run
flyctl wireguard create to create a WireGuard config. Use the following settings:
Region: dev DNS name for peer: Filename: fly.conf
Note: The default config sets Fly as your DNS resolver. If you don’t need Fly’s internal DNS features, edit
fly.conf and comment out the DNS line with a pound sign (
Finally, setup the tunnel in WireGuard:
- On Mac or Windows, open the WireGuard app and click
Import Tunnel(s) from File. Once imported, click
- On Linux, use the command line.
3. Create the reverse proxy app
mkdir tunnel && cd tunnel to create an empty app folder. Run
flyctl init to create a
fly.toml config file. Use the following settings
App name: Select builder: Image Select image: lukelambert/fly-dev-tunnel Internal port: 8080
4. Configure the reverse proxy
The reverse proxy is configured using two environment variables:
SUBDOMAINS: A comma-separated list in the format
subdomain:local_port. An underscore (
_) matches the default (catch all) domain.
UPSTREAM: The internal hostname of your local machine on the WireGuard network. Use the format
your-machine-name._peer.internalwith the name chosen in step 2.
fly.toml and add the following lines at the bottom, replacing the values with your own:
[experimental] private_network = "true" [env] SUBDOMAINS = "_:8000" UPSTREAM = "your-machine-name._peer.internal"
5. Deploy the reverse proxy
flyctl deploy. Once the app is deployed, you should have a tunnel from
https://your-app-name.fly.dev to port
8000 on your local machine.
6. (Optional) Connect custom (sub)domains
Visit the Apps dashboard and select your app. Under the Certificates section, follow the instructions to add a custom domain. You can also add a wildcard subdomain, but this incurs a monthly fee. To map subdomains to ports, update your
fly.toml and re-run
flyctl deploy. Example:
[experimental] private_network = "true" [env] SUBDOMAINS = "_:8000,app1:9001,app2:9002" UPSTREAM = "your-machine-name._peer.internal"
All traffic is proxied over IPv6, so your web service should bind to an IPv6 address. To take down the tunnel and prevent traffic from reaching your machine, simply deactivate the WireGuard tunnel.