# Running the service via TLS (optional)

## Bring your own certificate

Headscale can be configured to expose its web service via TLS. To configure the certificate and key file manually, set the `tls_cert_path` and `tls_key_path` configuration parameters. If the path is relative, it will be interpreted as relative to the directory the configuration file was read from.

```yaml title="config.yaml"
tls_cert_path: ""
tls_key_path: ""
```

The certificate should contain the full chain, else some clients, like the Tailscale Android client, will reject it.

## Let's Encrypt / ACME

To get a certificate automatically via [Let's Encrypt](https://letsencrypt.org/), set `tls_letsencrypt_hostname` to the desired certificate hostname. This name must resolve to the IP address(es) headscale is reachable on (i.e., it must correspond to the `server_url` configuration parameter). The certificate and Let's Encrypt account credentials will be stored in the directory configured in `tls_letsencrypt_cache_dir`. If the path is relative, it will be interpreted as relative to the directory the configuration file was read from.

```yaml title="config.yaml"
tls_letsencrypt_hostname: ""
tls_letsencrypt_listen: ":http"
tls_letsencrypt_cache_dir: ".cache"
tls_letsencrypt_challenge_type: HTTP-01
```

### Challenge types

Headscale only supports two values for `tls_letsencrypt_challenge_type`: `HTTP-01` (default) and `TLS-ALPN-01`.

#### HTTP-01

For `HTTP-01`, headscale must be reachable on port 80 for the Let's Encrypt automated validation, in addition to whatever port is configured in `listen_addr`. By default, headscale listens on port 80 on all local IPs for Let's Encrypt automated validation.

If you need to change the ip and/or port used by headscale for the Let's Encrypt validation process, set `tls_letsencrypt_listen` to the appropriate value. This can be handy if you are running headscale as a non-root user (or can't run `setcap`). Keep in mind, however, that Let's Encrypt will _only_ connect to port 80 for the validation callback, so if you change `tls_letsencrypt_listen` you will also need to configure something else (e.g. a firewall rule) to forward the traffic from port 80 to the ip:port combination specified in `tls_letsencrypt_listen`.

#### TLS-ALPN-01

For `TLS-ALPN-01`, headscale listens on the ip:port combination defined in `listen_addr`. Let's Encrypt will _only_ connect to port 443 for the validation callback, so if `listen_addr` is not set to port 443, something else (e.g. a firewall rule) will be required to forward the traffic from port 443 to the ip:port combination specified in `listen_addr`.

### Technical description

Headscale uses [autocert](https://pkg.go.dev/golang.org/x/crypto/acme/autocert), a Golang library providing [ACME protocol](https://en.wikipedia.org/wiki/Automatic_Certificate_Management_Environment) verification, to facilitate certificate renewals via [Let's Encrypt](https://letsencrypt.org/about/). Certificates will be renewed automatically, and the following can be expected:

- Certificates provided from Let's Encrypt have a validity of 3 months from date issued.
- Renewals are only attempted by headscale when 30 days or less remains until certificate expiry.
- Renewal attempts by autocert are triggered at a random interval of 30-60 minutes.
- No log output is generated when renewals are skipped, or successful.

#### Checking certificate expiry

If you want to validate that certificate renewal completed successfully, this can be done either manually, or through external monitoring software. Two examples of doing this manually:

1. Open the URL for your headscale server in your browser of choice, and manually inspecting the expiry date of the certificate you receive.
1. Or, check remotely from CLI using `openssl`:

```console
$ openssl s_client -servername [hostname] -connect [hostname]:443 | openssl x509 -noout -dates
(...)
notBefore=Feb  8 09:48:26 2024 GMT
notAfter=May  8 09:48:25 2024 GMT
```

#### Log output from the autocert library

As these log lines are from the autocert library, they are not strictly generated by headscale itself.

```plaintext
acme/autocert: missing server name
```

Likely caused by an incoming connection that does not specify a hostname, for example a `curl` request directly against the IP of the server, or an unexpected hostname.

```plaintext
acme/autocert: host "[foo]" not configured in HostWhitelist
```

Similarly to the above, this likely indicates an invalid incoming request for an incorrect hostname, commonly just the IP itself.

The source code for autocert can be found [here](https://cs.opensource.google/go/x/crypto/+/refs/tags/v0.19.0:acme/autocert/autocert.go)
