![Erik Johnston](/assets/img/avatar_default.png)
A surprising number of people are using the well-known method, and are simply copying the example configuration. This is problematic as the example includes an explicit port, which causes inbound federation requests to have the HTTP Host header include the port, upsetting some reverse proxies. Given that, we update the well-known example to be more explicit about the various ways you can set it up, and the consequence of using an explict port.
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MSC1711 Certificates FAQ
The goal of Synapse 0.99.0 is to act as a stepping stone to Synapse 1.0.0. It supports the r0.1 release of the server to server specification, but is compatible with both the legacy Matrix federation behaviour (pre-r0.1) as well as post-r0.1 behaviour, in order to allow for a smooth upgrade across the federation.
The most important thing to know is that Synapse 1.0.0 will require a valid TLS certificate on federation endpoints. Self signed certificates will not be sufficient.
Synapse 0.99.0 makes it easy to configure TLS certificates and will interoperate with both >= 1.0.0 servers as well as existing servers yet to upgrade.
It is critical that all admins upgrade to 0.99.0 and configure a valid TLS certificate. Admins will have 1 month to do so, after which 1.0.0 will be released and those servers without a valid certificate will not longer be able to federate with >= 1.0.0 servers.
Full details on how to carry out this configuration change is given below. A timeline and some frequently asked questions are also given below.
For more details and context on the release of the r0.1 Server/Server API and imminent Matrix 1.0 release, you can also see our main talk from FOSDEM 2019.
Contents
- Timeline
- Configuring certificates for compatibility with Synapse 1.0
- FAQ
- Synapse 0.99.0 has just been released, what do I need to do right now?
- How do I upgrade?
- What will happen if I do not set up a valid federation certificate immediately?
- What will happen if I do nothing at all?
- When do I need a SRV record or .well-known URI?
- Can I still use an SRV record?
- I have created a .well-known URI. Do I still need an SRV record?
- 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 I still need to give my TLS certificates to Synapse if I am using a 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?
Timeline
5th Feb 2019 - Synapse 0.99.0 is released.
All server admins are encouraged to upgrade.
0.99.0:
-
provides support for ACME to make setting up Let's Encrypt certs easy, as well as .well-known support.
-
does not enforce that a valid CA cert is present on the federation API, but rather makes it easy to set one up.
-
provides support for .well-known
Admins should upgrade and configure a valid CA cert. Homeservers that require a .well-known entry (see below), should retain their SRV record and use it alongside their .well-known record.
>= 5th March 2019 - Synapse 1.0.0 is released
1.0.0 will land no sooner than 1 month after 0.99.0, leaving server admins one month after 5th February to upgrade to 0.99.0 and deploy their certificates. In accordance with the the S2S spec 1.0.0 will enforce certificate validity. This means that any homeserver without a valid certificate after this point will no longer be able to federate with 1.0.0 servers.
Configuring certificates for compatibility with Synapse 1.0.0
If you do not currently have an SRV record
In this case, your server_name
points to the host where your Synapse is
running. There is no need to create a .well-known
URI or an SRV record, but
you will need to give Synapse a valid, signed, certificate.
The easiest way to do that is with Synapse's built-in ACME (Let's Encrypt) support. Full details are in ACME.md but, in a nutshell:
- Allow Synapse to listen on port 80 with
authbind
, or forward it from a reverse proxy. - Enable acme support in
homeserver.yaml
. - Move your old certificates out of the way.
- Restart Synapse.
If you do have an SRV record currently
If you are using an SRV record, your matrix domain (server_name
) may not
point to the same host that your Synapse is running on (the 'target
domain'). (If it does, you can follow the recommendation above; otherwise, read
on.)
Let's assume that your server_name
is example.com
, and your Synapse is
hosted at a target domain of customer.example.net
. Currently you should have
an SRV record which looks like:
_matrix._tcp.example.com. IN SRV 10 5 8000 customer.example.net.
In this situation, you have three choices for how to proceed:
Option 1: give Synapse a certificate for your matrix domain
Synapse 1.0 will expect your server to present a TLS certificate for your
server_name
(example.com
in the above example). You can achieve this by
doing one of the following:
-
Acquire a certificate for the
server_name
yourself (for example, usingcertbot
), and give it and the key to Synapse viatls_certificate_path
andtls_private_key_path
, or: -
Use Synapse's ACME support, and forward port 80 on the
server_name
domain to your Synapse instance.
Option 2: run Synapse behind a reverse proxy
If you have an existing reverse proxy set up with correct TLS certificates for 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).
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 give it a certificate for the matrix domain.
You can do this with a .well-known
file as follows:
-
Keep the SRV record in place - it is needed for backwards compatibility with Synapse 0.34 and earlier.
-
Give synapse a certificate corresponding to the target domain (
customer.example.net
in the above example). Currently Synapse's ACME support does not support this, so you will have to acquire a certificate yourself and give it to Synapse viatls_certificate_path
andtls_private_key_path
. -
Restart Synapse to ensure the new certificate is loaded.
-
Arrange for a
.well-known
file athttps://<server_name>/.well-known/matrix/server
with contents:{"m.server": "<target server name>"}
where the target server name is resolved as usual (i.e. SRV lookup, falling back to talking to port 8448).
In the above example, where synapse is listening on port 8000,
https://example.com/.well-known/matrix/server
should havem.server
set to one of:-
customer.example.net
─ with a SRV record on_matrix._tcp.customer.example.com
pointing to port 8000, or: -
customer.example.net
─ updating synapse to listen on the default port 8448, or: -
customer.example.net:8000
─ ensuring that if there is a reverse proxy oncustomer.example.net:8000
it correctly handles HTTP requests with Host header set tocustomer.example.net:8000
.
-
FAQ
Synapse 0.99.0 has just been released, what do I need to do right now?
Upgrade as soon as you can in preparation for Synapse 1.0.0, and update your TLS certificates as above.
What will happen if I do not set up a valid federation certificate immediately?
Nothing initially, but once 1.0.0 is in the wild it will not be possible to federate with 1.0.0 servers.
What will happen if I do nothing at all?
If the admin takes no action at all, and remains on a Synapse < 0.99.0 then the homeserver will be unable to federate with those who have implemented .well-known. Then, as above, once the month upgrade window has expired the homeserver will not be able to federate with any Synapse >= 1.0.0
When do I need a SRV record or .well-known URI?
If your homeserver listens on the default federation port (8448), and your
server_name
points to the host that your homeserver runs on, you do not need an
SRV record or .well-known/matrix/server
URI.
For instance, if you registered example.com
and pointed its DNS A record at a
fresh Upcloud VPS or similar, you could install Synapse 0.99 on that host,
giving it a server_name of example.com
, and it would automatically generate a
valid TLS certificate for you via Let's Encrypt and no SRV record or
.well-known
URI would be needed.
This is the common case, although you can add an SRV record or
.well-known/matrix/server
URI for completeness if you wish.
However, if your server does not listen on port 8448, or if your server_name
does not point to the host that your homeserver runs on, you will need to let
other servers know how to find it.
In this case, you should see "If you do have an SRV record currently" above.
Can I still use an SRV record?
Firstly, if you didn't need an SRV record before (because your server is listening on port 8448 of your server_name), you certainly don't need one now: the defaults are still the same.
If you previously had an SRV record, you can keep using it provided you are able to give Synapse a TLS certificate corresponding to your server name. For example, suppose you had the following SRV record, which directs matrix traffic for example.com to matrix.example.com:443:
_matrix._tcp.example.com. IN SRV 10 5 443 matrix.example.com
In this case, Synapse must be given a certificate for example.com - or be configured to acquire one from Let's Encrypt.
If you are unable to give Synapse a certificate for your server_name, you will also need to use a .well-known URI instead. However, see also "I have created a .well-known URI. Do I still need an SRV record?".
I have created a .well-known URI. Do I still need an SRV record?
As of Synapse 0.99, Synapse will first check for the existence of a .well-known
URI and follow any delegation it suggests. It will only then check for the
existence of an SRV record.
That means that the SRV record will often be redundant. However, you should
remember that there may still be older versions of Synapse in the federation
which do not understand .well-known
URIs, so if you removed your SRV record you
would no longer be able to federate with them.
It is therefore best to leave the SRV record in place for now. Synapse 0.34 and earlier will follow the SRV record (and not care about the invalid certificate). Synapse 0.99 and later will follow the .well-known URI, with the correct certificate chain.
It used to work just fine, why are you breaking everything?
We have always wanted Matrix servers to be as easy to set up as possible, and so back when we started federation in 2014 we didn't want admins to have to go through the cumbersome process of buying a valid TLS certificate to run a server. This was before Let's Encrypt came along and made getting a free and valid TLS certificate straightforward. So instead, we adopted a system based on Perspectives: an approach where you check a set of "notary servers" (in practice, homeservers) to vouch for the validity of a certificate rather than having it signed by a CA. As long as enough different notaries agree on the certificate's validity, then it is trusted.
However, in practice this has never worked properly. Most people only use the default notary server (matrix.org), leading to inadvertent centralisation which we want to eliminate. Meanwhile, we never implemented the full consensus algorithm to query the servers participating in a room to determine consensus on whether a given certificate is valid. This is fiddly to get right (especially in face of sybil attacks), and we found ourselves questioning whether it was worth the effort to finish the work and commit to maintaining a secure certificate validation system as opposed to focusing on core Matrix development.
Meanwhile, Let's Encrypt came along in 2016, and put the final nail in the coffin of the Perspectives project (which was already pretty dead). So, the Spec Core Team decided that a better approach would be to mandate valid TLS certificates for federation alongside the rest of the Web. More details can be found in MSC1711.
This results in a breaking change, which is disruptive, but absolutely critical for the security model. However, the existence of Let's Encrypt as a trivial way to replace the old self-signed certificates with valid CA-signed ones helps smooth things over massively, especially as Synapse can now automate Let's Encrypt certificate generation if needed.
Can I manage my own certificates rather than having Synapse renew certificates itself?
Yes, you are welcome to manage your certificates yourself. Synapse will only 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?
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.
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
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
check it is when attempting to fetch the server keys - and generally this is
delegated via matrix.org
, which is on 0.99.0.
However, there is a bug in Synapse 0.99.0 4554 which prevents Synapse from starting if you do not give it a TLS certificate. To work around 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.
How do I tell Synapse to reload my keys/certificates after I replace them?
Synapse will reload the keys and certificates when it receives a SIGHUP - for
example kill -HUP $(cat homeserver.pid)
. Alternatively, simply restart
Synapse, though this will result in downtime while it restarts.