Tailscale VPN :: gokrazy

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# Tailscale VPN

Tailscale’s website reads:

> A secure network that just works

> Zero config VPN. Installs on any device in minutes, manages firewall rules for you, and works from anywhere.

gokrazy-based devices are no exception! This guide shows you how to use Tailscale with gokrazy.

Tailscale’s networking will come in handy when accessing your gokrazy server remotely (no static DHCP leases, port-forwarding and DynDNS required!), or even to secure your communication when gokrazy is connected to an unencrypted WiFi network.

## Requirements

- Package `tailscale.com` v1.56.1 or later (latest version used automatically unless you have the package already in go.mod)
- Volume `/perm/` needs to be initialized (instructions use `github.com/gokrazy/mkfs` to initialize) to persist authentication over reboots.

## Step 1. include the tailscale packages

Add the Tailscale daemon `tailscaled` and CLI `tailscale` Go packages to your gokrazy instance:

    gok add tailscale.com/cmd/tailscaled
    gok add tailscale.com/cmd/tailscale
    # Automatically initialize a file system on the /perm partition on first boot:
    gok add github.com/gokrazy/mkfs

## Step 2. set command-line flags

Then, open your instance’s `config.json` in your editor:

    gok edit

And configure Package config: Command-line flags for Option A or Option B:

Option A: interactive authentication

    {
        "Hostname": "ts",
        "Packages": [
            "github.com/gokrazy/fbstatus",
            "github.com/gokrazy/hello",
            "github.com/gokrazy/serial-busybox",
            "github.com/gokrazy/breakglass",
            "tailscale.com/cmd/tailscaled",
            "tailscale.com/cmd/tailscale",
            "github.com/gokrazy/mkfs"
        ],
        "PackageConfig": {
            "tailscale.com/cmd/tailscale": {
                "CommandLineFlags": [
                    "up"
                ]
            }
        }
    }

Option B: unattended authentication with auth key

Alternatively, navigate to Tailscale console and open Settings / Keys. Generate auth key.

Include the key to tailscale flags:

    {
        "Hostname": "ts",
        "Packages": [
            "github.com/gokrazy/fbstatus",
            "github.com/gokrazy/hello",
            "github.com/gokrazy/serial-busybox",
            "github.com/gokrazy/breakglass",
            "tailscale.com/cmd/tailscaled",
            "tailscale.com/cmd/tailscale",
            "github.com/gokrazy/mkfs"
        ],
        "PackageConfig": {
            "tailscale.com/cmd/tailscale": {
                "CommandLineFlags": [
                    "up",
                    "--auth-key=tskey-AAAAAAAAAAAA-AAAAAAAAAAAAAAAAAAAAAA"
                ]
            }
        }
    }

Then, deploy as usual:

    gok update

## Step 3. authenticate (interactive only)

Skip this step if you are using option B with auth key.

1. Navigate to your gokrazy web interface with browser using the URL displayed by the `gok` CLI.
2. Open the service `/user/tailscale` and find the login URL.
3. Open the link with browser and log in to Tailscale and authorize the client.

## Step 4. disable key expiry (optional)

You are now connected to Tailscale and you can access your gokrazy instance over Tailscale.

Tailscale requires re-authentication periodically. You can disable key expiry from Tailscale console for the gokrazy instance to not require login every 3 months.

## Optional: Using gokrazy as a Tailscale subnet router

To allow hosts in your Tailnet to access devices in your network other than your gokrazy appliance, you can set up Tailscale as a subnet router.

    {
        "Hostname": "ts",
        "Packages": [
            "github.com/gokrazy/serial-busybox",
            "tailscale.com/cmd/tailscaled",
            "tailscale.com/cmd/tailscale"
        ],
        "PackageConfig": {
            "tailscale.com/cmd/tailscale": {
                "CommandLineFlags": [
                    "up",
                    "--advertise-routes=192.168.0.0/24"
                ]
            }
        }
    }

Starting Tailscale version v1.64, IP forwarding is automatically enabled on Gokrazy.

## Optional: Accessing gokrazy using Tailscale SSH

To access the gokrazy appliance using SSH authenticating using Tailscale, you can enable Tailscale SSH.

    {
        "Hostname": "ts",
        "Packages": [
            "github.com/gokrazy/serial-busybox",
            "tailscale.com/cmd/tailscaled",
            "tailscale.com/cmd/tailscale"
        ],
        "PackageConfig": {
            "tailscale.com/cmd/tailscale": {
                "CommandLineFlags": [
                    "up",
                    "--ssh=true"
                ]
            }
        }
    }

Note that Tailscale SSH needs to be allowed by your Tailnet ACL. You can configure to allow, for example, each user to access their own devices using Tailscale SSH, or define which hosts users can access.

## Optional: Tailscale network for other programs

Before Tailscale v1.56.1, Tailscale used Userspace networking mode on gokrazy, meaning you needed to use Tailscale as an HTTP proxy to establish outgoing connections into your tailnet.

With Tailscale v1.56.1 and newer, programs running on gokrazy can connect to other devices in your tailnet without extra steps! 🎉 DNS resolution and TCP connections work out of the box.

## Optional: Tailscale Go listener

Before Tailscale v1.56.1, Tailscale used Userspace networking mode on gokrazy, meaning you needed to use the tsnet package if you wanted to restrict a listener to Tailscale.

With Tailscale v1.56.1 and newer, you can listen on Tailscale addresses and use LocalClient.WhoIs to obtain the remote identity:

    package main

    import (
    	"flag"
    	"fmt"
    	"log"
    	"net/http"

    	"tailscale.com/client/tailscale"
    )

    func main() {
    	listen := flag.String("listen", "gokrazy.monkey-turtle.ts.net:8111", "[host]:port listen address")
    	allowedUser := flag.String("allowed_user", "", "the name of a tailscale user to allow")
    	flag.Parse()
    	log.Printf("starting HTTP listener on %s", *listen)
    	var ts tailscale.LocalClient
    	httpsrv := &http.Server{
    		Addr: *listen,
    		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    			who, err := ts.WhoIs(r.Context(), r.RemoteAddr)
    			if err != nil {
    				http.Error(w, err.Error(), http.StatusInternalServerError)
    				return
    			}
    			if who.UserProfile.LoginName != *allowedUser || *allowedUser == "" {
    				err := fmt.Sprintf("you are logged in as %q (userprofile: %+v), but -allowed_user flag does not match!", who.UserProfile.LoginName, who.UserProfile)
    				log.Printf("forbidden: %v", err)
    				http.Error(w, err, http.StatusForbidden)
    				return
    			}
    			fmt.Fprintf(w, "hey there, %q! this message is served via tailscale from gokrazy!", who.UserProfile.LoginName)
    		}),
    	}
    	log.Fatal(httpsrv.ListenAndServe())
    }

1. Deploy this program to your gokrazy device
2. Open the listening address in your browser, e.g. http://gokrazy.monkey-turtle.ts.net:8111
3. Specify the `--allowed_user` flag to verify that tailscale authentication works as expected