Clarifications for reverse proxy docs (#4607)

Factor out the reverse proxy info to a separate file, add some more info on
reverse-proxying the federation port.

3 files changed, 110 insertions, 11 deletions

diff --git a/docs/MSC1711_certificates_FAQ.md b/docs/MSC1711_certificates_FAQ.md
index 0a781d00e3..2c52b0d517 100644
--- a/docs/MSC1711_certificates_FAQ.md
+++ b/docs/MSC1711_certificates_FAQ.md
@@ -42,9 +42,9 @@ imminent Matrix 1.0 release, you can also see our
   * It used to work just fine, why are you breaking everything?
   * Can I manage my own certificates rather than having Synapse renew
     certificates itself?
-  * Do you still recommend against using a reverse-proxy on the federation port?
+  * Do you still recommend against using a reverse proxy on the federation port?
   * Do I still need to give my TLS certificates to Synapse if I am using a
-    reverse-proxy?
+    reverse proxy?
   * Do I need the same certificate for the client and federation port?
   * How do I tell Synapse to reload my keys/certificates after I replace them?
 
@@ -132,6 +132,9 @@ your domain, you can simply route all traffic through the reverse proxy by
 updating the SRV record appropriately (or removing it, if the proxy listens on
 8448).
 
+See [reverse_proxy.rst](reverse_proxy.rst) for information on setting up a
+reverse proxy.
+
 #### Option 3: add a .well-known file to delegate your matrix traffic
 
 This will allow you to keep Synapse on a separate domain, without having to
@@ -297,17 +300,20 @@ attempt to obtain certificates from Let's Encrypt if you configure it to do
 so.The only requirement is that there is a valid TLS cert present for
 federation end points.
 
-### Do you still recommend against using a reverse-proxy on the federation port?
+### 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
+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.rst](reverse_proxy.rst) 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?
 
 Practically speaking, this is no longer necessary.
 
-If you are using a reverse-proxy for all of your TLS traffic, then you can set
+If you are using a reverse proxy for all of your TLS traffic, then you can set
 `no_tls: True`. 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
@@ -321,9 +327,9 @@ this, you can give it any TLS certificate at all. This will be fixed soon.
 
 ### Do I need the same certificate for the client and federation port?
 
-No. There is nothing stopping you doing so, particularly if you are using a
-reverse-proxy. However, Synapse will use the same certificate on any ports
-where TLS is configured.
+No. There is nothing stopping you from using different certificates,
+particularly if you are using a reverse proxy. However, Synapse will use the
+same certificate on any ports where TLS is configured.
 
 ### How do I tell Synapse to reload my keys/certificates after I replace them?
 
diff --git a/docs/reverse_proxy.rst b/docs/reverse_proxy.rst
new file mode 100644
index 0000000000..d8aaac8a08
--- /dev/null
+++ b/docs/reverse_proxy.rst
@@ -0,0 +1,94 @@
+Using a reverse proxy with Synapse
+==================================
+
+It is recommended to put a reverse proxy such as
+`nginx <https://nginx.org/en/docs/http/ngx_http_proxy_module.html>`_,
+`Apache <https://httpd.apache.org/docs/current/mod/mod_proxy_http.html>`_,
+`Caddy <https://caddyserver.com/docs/proxy>`_ or
+`HAProxy <https://www.haproxy.org/>`_ in front of Synapse. One advantage of
+doing so is that it means that you can expose the default https port (443) to
+Matrix clients without needing to run Synapse with root privileges.
+
+**NOTE**: Your reverse proxy must not 'canonicalise' or 'normalise' the
+requested URI in any way (for example, by decoding ``%xx`` escapes). Beware
+that Apache *will* canonicalise URIs unless you specifify ``nocanon``.
+
+When setting up a reverse proxy, remember that Matrix clients and other Matrix
+servers do not necessarily need to connect to your server via the same server
+name or port. Indeed, clients will use port 443 by default, whereas servers
+default to port 8448. Where these are different, we refer to the 'client port'
+and the 'federation port'. See `Setting up federation
+<../README.rst#setting-up-federation>`_ for more details of the algorithm used for
+federation connections.
+
+Let's assume that we expect clients to connect to our server at
+``https://matrix.example.com``, and other servers to connect at
+``https://example.com:8448``. Here are some example configurations:
+
+* nginx::
+
+      server {
+          listen 443 ssl;
+          listen [::]:443 ssl;
+          server_name matrix.example.com;
+
+          location /_matrix {
+              proxy_pass http://localhost:8008;
+              proxy_set_header X-Forwarded-For $remote_addr;
+          }
+      }
+
+      server {
+          listen 8448 ssl default_server;
+          listen [::]:8448 ssl default_server;
+          server_name example.com;
+
+          location / {
+              proxy_pass http://localhost:8008;
+              proxy_set_header X-Forwarded-For $remote_addr;
+          }
+      }
+
+* Caddy::
+
+      matrix.example.com {
+        proxy /_matrix http://localhost:8008 {
+          transparent
+        }
+      }
+
+      example.com:8448 {
+        proxy / http://localhost:8008 {
+          transparent
+        }
+      }
+
+* Apache (note the ``nocanon`` options here!)::
+
+      <VirtualHost *:443>
+          SSLEngine on
+          ServerName matrix.example.com;
+
+          <Location /_matrix>
+              ProxyPass http://127.0.0.1:8008/_matrix nocanon
+              ProxyPassReverse http://127.0.0.1:8008/_matrix
+          </Location>
+      </VirtualHost>
+
+      <VirtualHost *:8448>
+          SSLEngine on
+          ServerName example.com;
+
+          <Location />
+              ProxyPass http://127.0.0.1:8008/_matrix nocanon
+              ProxyPassReverse http://127.0.0.1:8008/_matrix
+          </Location>
+      </VirtualHost>
+
+You will also want to set ``bind_addresses: ['127.0.0.1']`` and ``x_forwarded: true``
+for port 8008 in ``homeserver.yaml`` to ensure that client IP addresses are
+recorded correctly.
+
+Having done so, you can then use ``https://matrix.example.com`` (instead of
+``https://matrix.example.com:8448``) as the "Custom server" when connecting to
+Synapse from a client.
diff --git a/docs/workers.rst b/docs/workers.rst
index 101e950020..dd3a84ba0d 100644
--- a/docs/workers.rst
+++ b/docs/workers.rst
@@ -26,9 +26,8 @@ Configuration
 To make effective use of the workers, you will need to configure an HTTP
 reverse-proxy such as nginx or haproxy, which will direct incoming requests to
 the correct worker, or to the main synapse instance. Note that this includes
-requests made to the federation port. The caveats regarding running a
-reverse-proxy on the federation port still apply (see
-https://github.com/matrix-org/synapse/blob/master/README.rst#reverse-proxying-the-federation-port).
+requests made to the federation port. See `<reverse_proxy.rst>`_ for
+information on setting up a reverse proxy.
 
 To enable workers, you need to add two replication listeners to the master
 synapse, e.g.::