Split the delegating documentation out of federate.md and trim it down

1 files changed, 87 insertions, 0 deletions

diff --git a/docs/delegate.md b/docs/delegate.md
new file mode 100644
index 0000000000..4126fffe71
--- /dev/null
+++ b/docs/delegate.md
@@ -0,0 +1,87 @@
+# Delegation
+
+For a more flexible configuration, you can have `server_name`
+resources (eg: `@user:example.com`) served by a different host and
+port (eg: `synapse.example.com:443`).
+
+Without configuring delegation, the matrix federation will
+expect to find your server via `example.com:8448`. The following methods
+allow you retain a `server_name` of `example.com` so that your user IDs, room
+aliases, etc continue to look like `*:example.com`, whilst having your
+federation traffic routed to a different server (e.g. `synapse.example.com`).
+
+## .well-known delegation
+
+To use this method, you need to be able to alter the
+`server_name` 's https server to serve the `/.well-known/matrix/server`
+URL. Having an active server (with a valid TLS certificate) serving your
+`server_name` domain is out of the scope of this documentation.
+
+The URL `https://<server_name>/.well-known/matrix/server` should
+return a JSON structure containing the key `m.server` like so:
+
+```json
+{
+    "m.server": "<synapse.server.name>[:<yourport>]"
+}
+```
+
+In our example, this would mean that URL `https://example.com/.well-known/matrix/server`
+should return:
+
+```json
+{
+    "m.server": "synapse.example.com:443"
+}
+```
+
+Note, specifying a port is optional. If no port is specified, then it defaults
+to 8448.
+
+Most installations will not need to configure .well-known. However, it can be
+useful in cases where the admin is hosting on behalf of someone else and
+therefore cannot gain access to the necessary certificate. With .well-known,
+federation servers will check for a valid TLS certificate for the delegated
+hostname (in our example: `synapse.example.com`).
+
+## Delegation FAQ
+
+### When do I need delegation?
+
+If your homeserver's APIs are accessible on the default federation port (8448)
+and the domain your `server_name` points to, you do not need any delegation.
+
+For instance, if you registered `example.com` and pointed its DNS A record at a
+fresh server, you could install Synapse on that host, giving it a `server_name`
+of `example.com`, and once a reverse proxy has been set up to proxy all requests
+sent to the port `8448` and serve TLS certificates for `example.com`, you
+wouldn't need any delegation set up.
+
+**However**, if your homeserver's APIs aren't accessible on port 8448 and on the
+domain `server_name` points to, you will need to let other servers know how to
+find it using delegation.
+
+### Do you still recommend against using a reverse proxy on the federation port?
+
+We no longer actively recommend against using a reverse proxy. Many admins will
+find it easier to direct federation traffic to a reverse proxy and manage their
+own TLS certificates, and this is a supported configuration.
+
+See [reverse_proxy.md](reverse_proxy.md) for information on setting up a
+reverse proxy.
+
+### Do I still need to give my TLS certificates to Synapse if I am using a reverse proxy?
+
+This is no longer necessary. If you are using a reverse proxy for all of your
+TLS traffic, then you can set `no_tls: True` in the Synapse config.
+
+In that case, the only reason Synapse needs the certificate is to populate a legacy
+`tls_fingerprints` field in the federation API. This is ignored by Synapse 0.99.0
+and later, and the only time pre-0.99 Synapses will check it is when attempting to
+fetch the server keys - and generally this is delegated via `matrix.org`, which
+is running a modern version of Synapse.
+
+### Do I need the same certificate for the client and federation port?
+
+No. There is nothing stopping you from using different certificates,
+particularly if you are using a reverse proxy.
\ No newline at end of file