126 lines
5.3 KiB
Markdown
126 lines
5.3 KiB
Markdown
Setting up Federation
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=====================
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Federation is the process by which users on different servers can participate
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in the same room. For this to work, those other servers must be able to contact
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yours to send messages.
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The ``server_name`` configured in the Synapse configuration file (often
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``homeserver.yaml``) defines how resources (users, rooms, etc.) will be
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identified (eg: ``@user:example.com``, ``#room:example.com``). By
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default, it is also the domain that other servers will use to
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try to reach your server (via port 8448). This is easy to set
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up and will work provided you set the ``server_name`` to match your
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machine's public DNS hostname, and provide Synapse with a TLS certificate
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which is valid for your ``server_name``.
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Once you have completed the steps necessary to federate, you should be able to
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join a room via federation. (A good place to start is ``#synapse:matrix.org``
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- a room for Synapse admins.)
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## Delegation
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For a more flexible configuration, you can have ``server_name``
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resources (eg: ``@user:example.com``) served by a different host and
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port (eg: ``synapse.example.com:443``). There are two ways to do this:
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- adding a ``/.well-known/matrix/server`` URL served on ``https://example.com``.
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- adding a DNS ``SRV`` record in the DNS zone of domain
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``example.com``.
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Without configuring delegation, the matrix federation will
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expect to find your server via ``example.com:8448``. The following methods
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allow you retain a `server_name` of `example.com` so that your user IDs, room
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aliases, etc continue to look like `*:example.com`, whilst having your
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federation traffic routed to a different server.
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### .well-known delegation
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To use this method, you need to be able to alter the
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``server_name`` 's https server to serve the ``/.well-known/matrix/server``
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URL. Having an active server (with a valid TLS certificate) serving your
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``server_name`` domain is out of the scope of this documentation.
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The URL ``https://<server_name>/.well-known/matrix/server`` should
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return a JSON structure containing the key ``m.server`` like so:
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{
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"m.server": "<synapse.server.name>[:<yourport>]"
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}
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In our example, this would mean that URL ``https://example.com/.well-known/matrix/server``
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should return:
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{
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"m.server": "synapse.example.com:443"
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}
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Note, specifying a port is optional. If a port is not specified an SRV lookup
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is performed, as described below. If the target of the
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delegation does not have an SRV record, then the port defaults to 8448.
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Most installations will not need to configure .well-known. However, it can be
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useful in cases where the admin is hosting on behalf of someone else and
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therefore cannot gain access to the necessary certificate. With .well-known,
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federation servers will check for a valid TLS certificate for the delegated
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hostname (in our example: ``synapse.example.com``).
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.well-known support first appeared in Synapse v0.99.0. To federate with older
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servers you may need to additionally configure SRV delegation. Alternatively,
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encourage the server admin in question to upgrade :).
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### DNS SRV delegation
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To use this delegation method, you need to have write access to your
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``server_name`` 's domain zone DNS records (in our example it would be
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``example.com`` DNS zone).
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This method requires the target server to provide a
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valid TLS certificate for the original ``server_name``.
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You need to add a SRV record in your ``server_name`` 's DNS zone with
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this format:
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_matrix._tcp.<yourdomain.com> <ttl> IN SRV <priority> <weight> <port> <synapse.server.name>
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In our example, we would need to add this SRV record in the
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``example.com`` DNS zone:
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_matrix._tcp.example.com. 3600 IN SRV 10 5 443 synapse.example.com.
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Once done and set up, you can check the DNS record with ``dig -t srv
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_matrix._tcp.<server_name>``. In our example, we would expect this:
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$ dig -t srv _matrix._tcp.example.com
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_matrix._tcp.example.com. 3600 IN SRV 10 0 443 synapse.example.com.
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Note that the target of a SRV record cannot be an alias (CNAME record): it has to point
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directly to the server hosting the synapse instance.
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## Troubleshooting
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You can use the [federation tester](
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<https://matrix.org/federationtester>) to check if your homeserver is
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configured correctly. Alternatively try the [JSON API used by the federation tester](https://matrix.org/federationtester/api/report?server_name=DOMAIN).
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Note that you'll have to modify this URL to replace ``DOMAIN`` with your
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``server_name``. Hitting the API directly provides extra detail.
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The typical failure mode for federation is that when the server tries to join
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a room, it is rejected with "401: Unauthorized". Generally this means that other
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servers in the room could not access yours. (Joining a room over federation is
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a complicated dance which requires connections in both directions).
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Another common problem is that people on other servers can't join rooms that
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you invite them to. This can be caused by an incorrectly-configured reverse
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proxy: see [reverse_proxy.rst](<reverse_proxy.rst>) for instructions on how to correctly
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configure a reverse proxy.
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## Running a Demo Federation of Synapses
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If you want to get up and running quickly with a trio of homeservers in a
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private federation, there is a script in the ``demo`` directory. This is mainly
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useful just for development purposes. See [demo/README](<../demo/README>).
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