continuwuity/docs/advanced/delegation.mdx

# Delegation/split-domain deployment

Matrix allows clients and servers to discover a homeserver's "true" destination via **`.well-known` delegation**. This is especially useful if you would like to:

- Serve Continuwuity on a subdomain while having only the base domain for your usernames
- Use a port other than `:8448` for server-to-server connections

This guide will show you how to have `@user:example.com` usernames while serving Continuwuity on `https://matrix.example.com`. It assumes you are using port 443 for both client-to-server connections and server-to-server federation.

## Configuration

First, ensure you have set up A/AAAA records for `matrix.example.com` and `example.com` pointing to your IP.

Then, ensure that the `server_name` field matches your intended username suffix. If this is not the case, you **MUST** wipe the database directory and reinstall Continuwuity with your desired `server_name`.

Then, in the `[global.well_known]` section of your config file, add the following fields:

```toml
[global.well_known]

client = "https://matrix.example.com"

# port number MUST be specified
server = "matrix.example.com:443"

# (optional) customize your support contacts
# Defaults to members of #admin room if unset
#support_page =
#support_role = "m.role.admin"
#support_email =
#support_mxid = "@user:example.com"
```

Alternatively if you are using Docker, you can set the `CONTINUWUITY_WELL_KNOWN` environment variable as below:

```yaml
services:
  continuwuity:
    ...
    environment:
      CONTINUWUITY_WELL_KNOWN: |
        {
        client=https://matrix.example.com,
        server=matrix.example.com:443
        }

      # You can also configure individual .well-knowns as below
      # CONTINUWUITY_WELL_KNOWN__CLIENT: https://matrix.example.com
      # CONTINUWUITY_WELL_KNOWN__SERVER: matrix.example.com:443
```

## Serving with a reverse proxy

After doing the steps above, Continuwuity will serve these 3 JSON files:

- `/.well-known/matrix/client`: for Client-Server discovery
- `/.well-known/matrix/server`: for Server-Server (federation) discovery
- `/.well-known/matrix/support`: admin contact details (strongly recommended to have)

To enable full discovery, you will need to reverse proxy these paths from the base domain back to Continuwuity.

<details>

<summary>For Caddy</summary>

```
matrix.example.com:443 {
  reverse_proxy 127.0.0.1:8008
}

example.com:443 {
  reverse_proxy /.well-known/matrix* 127.0.0.1:8008
}
```

</details>

<details>

<summary>For Traefik (via Docker labels)</summary>

```
services:
  continuwuity:
    ...
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.continuwuity.rule=(Host(`matrix.example.com`) || (Host(`example.com`) && PathPrefix(`/.well-known/matrix`)))"
      - "traefik.http.routers.continuwuity.service=continuwuity"
      - "traefik.http.services.continuwuity.loadbalancer.server.port=8008"
```

</details>

Restart Continuwuity and your reverse proxy. Once that's done, visit these routes and check that the responses match the examples below:

<details open>

<summary>`https://example.com/.well-known/matrix/server`</summary>

```json
{
  "m.server": "matrix.example.com:443"
}
```

</details>

<details open>

<summary>`https://example.com/.well-known/matrix/client`</summary>

```json
{
  "m.homeserver": {
    "base_url": "https://matrix.example.com/"
  }
}
```

</details>

## Troubleshooting

### Cannot log in with web clients

Make sure there is an `Access-Control-Allow-Origin: *` header in your `/.well-known/matrix/client` path. While Continuwuity serves this header by default, it may be dropped by reverse proxies or other middlewares.

---

## Using SRV records (not recommended)

:::warning
The following methods are **not recommended** due to increased complexity with little benefits. If you have already set up `.well-known` delegation as above, you can safely skip this part.
:::

The following methods uses SRV DNS records and only work with federation traffic. They are only included for completeness.

<details>

<summary>Using only SRV records</summary>

If you can't set up `/.well-known/matrix/server` on :443 for some reason, you can set up a SRV record (via your DNS provider) as below:

- Service and name: `_matrix-fed._tcp.example.com.`
- Priority: `10` (can be any number)
- Weight: `10` (can be any number)
- Port: `443`
- Target: `matrix.example.com.`

On the target's IP at port 443, you must configure a valid route and cert for your server name, `example.com`. Therefore, this method only works to redirect traffic into the right IP/port combo, and can not delegate your federation to a different domain.

</details>

<details>

<summary>Using SRV records + .well-known</summary>

You can also set up `/.well-known/matrix/server` with a delegated domain but no ports:

```toml
[global.well_known]
server = "matrix.example.com"
```

Then, set up a SRV record (via your DNS provider) to announce the port number as below:

- Service and name: `_matrix-fed._tcp.matrix.example.com.`
- Priority: `10` (can be any number)
- Weight: `10` (can be any number)
- Port: `443`
- Target: `matrix.example.com.`

On the target's IP at port 443, you'll need to provide a valid route and cert for `matrix.example.com`. It provides the same feature as pure `.well-known` delegation, albeit with more parts to handle.

</details>

<details>

<summary>Using SRV records as a fallback for .well-known delegation</summary>

Assume your delegation is as below:

```toml
[global.well_known]
server = "example.com:443"
```

If your Continuwuity instance becomes temporarily unreachable, other servers will not be able to find your `/.well-known/matrix/server` file, and defaults to using `server_name:8448`. This incorrect cache can persist for a long time, and would hinder re-federation when your server eventually comes back online.

If you want other servers to default to using port :443 even when it is offline, you could set up a SRV record (via your DNS provider) as follows:

- Service and name: `_matrix-fed._tcp.example.com.`
- Priority: `10` (can be any number)
- Weight: `10` (can be any number)
- Port: `443`
- Target: `example.com.`

On the target's IP at port 443, you'll need to provide a valid route and cert for `example.com`.

</details>

---

## Related Documentation

See the following Matrix Specs for full details on client/server resolution mechanisms:

- [Server-to-Server resolution](https://spec.matrix.org/v1.17/server-server-api/#resolving-server-names) (see this for more information on SRV records)
- [Client-to-Server resolution](https://spec.matrix.org/v1.17/client-server-api/#server-discovery)
- [MSC1929: Homeserver Admin Contact and Support page](https://github.com/matrix-org/matrix-spec-proposals/pull/1929)