dns_hostname = "dns.example.com";
      # optional (default = 3000)
      timeout_ms = 3000;
    }
  ];
}
```

#### QUIC {#module-services-crab-hole-quic}
QUIC has identical settings to the HTTPS protocol.
Since by default it doesn't run on the standard HTTPS port, you shouldn't need a reverse proxy.
Make sure the service has permissions to access the certificate and key.
```nix
{
  services.crab-hole.settings.downstream = [
    {
      protocol = "quic";
      listen = "127.0.0.1";
      port = 853;
      certificate = ./dns.example.com.crt;
      key = "/dns.example.com.key";
      # optional
      dns_hostname = "dns.example.com";
      # optional (default = 3000)
      timeout_ms = 3000;
    }
  ];
}
```

### Upstream options {#module-services-crab-hole-upstream-options}
You can set additional options of the underlying DNS server. A full list of all the options can be found in the [hickory-dns documentation](https://docs.rs/trust-dns-resolver/0.23.0/trust_dns_resolver/config/struct.ResolverOpts.html).

This can look like the following example.
```nix
{
  services.crab-hole.settings.upstream.options = {
    validate = false;
  };
}
```

#### DNSSEC Issues {#module-services-crab-hole-dnssec}
Due to an upstream issue of [hickory-dns](https://github.com/hickory-dns/hickory-dns/issues/2429), sites without DNSSEC will not be resolved if `validate = true`.
Only DNSSEC capable sites will be resolved with this setting.
To prevent this, set `validate = false` or omit the `[upstream.options]`.

### API {#module-services-crab-hole-api}
The API allows a user to fetch statistic and information about the crab-hole instance.
Basic information is available for everyone, while more detailed information is secured by a key, which will be set with the `admin_key` option.

```nix
{
  services.crab-hole.settings.api = {
    listen = "127.0.0.1";
    port = 8080;
    # optional (default = false)
    show_doc = true; # OpenAPI doc loads content from third party websites
    # optional
    admin_key = "1234";
  };
}

```

The documentation can be enabled separately for the instance with `show_doc`.
This will then create an additional webserver, which hosts the API documentation.
An additional resource is in work in the [crab-hole repository](https://github.com/LuckyTurtleDev/crab-hole).

## Troubleshooting {#module-services-crab-hole-troubleshooting}
You can check for errors using `systemctl status crab-hole` or `journalctl -xeu crab-hole.service`.

### Invalid config {#module-services-crab-hole-invalid-config}
Some options of the service are in freeform and not type checked.
This can lead to a config which is not valid or cannot be parsed by crab-hole.
The error message will tell you what config value could not be parsed.
For more information check the [example config](https://github.com/LuckyTurtleDev/crab-hole/blob/main/example-config.toml).

### Permission Error {#module-services-crab-hole-permission-error}
It can happen that the created certificates for TLS, HTTPS or QUIC are owned by another user or group.
For ACME for example this would be `acme:acme`.
To give the crab-hole service access to these files, the group which owns the certificate can be added as a supplementary group to the service.
For ACME for example:
```nix
{ services.crab-hole.supplementaryGroups = [ "acme" ]; }
```