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-# MSC1711 Certificates FAQ
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-
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-## Historical Note
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-This document was originally written to guide server admins through the upgrade
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-path towards Synapse 1.0. Specifically,
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-[MSC1711](https://github.com/matrix-org/matrix-doc/blob/main/proposals/1711-x509-for-federation.md)
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-required that all servers present valid TLS certificates on their federation
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-API. Admins were encouraged to achieve compliance from version 0.99.0 (released
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-in February 2019) ahead of version 1.0 (released June 2019) enforcing the
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-certificate checks.
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-
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-Much of what follows is now outdated since most admins will have already
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-upgraded, however it may be of use to those with old installs returning to the
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-project.
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-
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-If you are setting up a server from scratch you almost certainly should look at
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-the [installation guide](setup/installation.md) instead.
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-
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-## Introduction
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-The goal of Synapse 0.99.0 is to act as a stepping stone to Synapse 1.0.0. It
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-supports the r0.1 release of the server to server specification, but is
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-compatible with both the legacy Matrix federation behaviour (pre-r0.1) as well
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-as post-r0.1 behaviour, in order to allow for a smooth upgrade across the
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-federation.
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-
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-The most important thing to know is that Synapse 1.0.0 will require a valid TLS
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-certificate on federation endpoints. Self signed certificates will not be
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-sufficient.
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-
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-Synapse 0.99.0 makes it easy to configure TLS certificates and will
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-interoperate with both >= 1.0.0 servers as well as existing servers yet to
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-upgrade.
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-
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-**It is critical that all admins upgrade to 0.99.0 and configure a valid TLS
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-certificate.** Admins will have 1 month to do so, after which 1.0.0 will be
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-released and those servers without a valid certificate will not longer be able
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-to federate with >= 1.0.0 servers.
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-
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-Full details on how to carry out this configuration change is given
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-[below](#configuring-certificates-for-compatibility-with-synapse-100). A
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-timeline and some frequently asked questions are also given below.
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-
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-For more details and context on the release of the r0.1 Server/Server API and
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-imminent Matrix 1.0 release, you can also see our
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-[main talk from FOSDEM 2019](https://matrix.org/blog/2019/02/04/matrix-at-fosdem-2019/).
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-
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-## Timeline
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-
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-**5th Feb 2019 - Synapse 0.99.0 is released.**
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-
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-All server admins are encouraged to upgrade.
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-
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-0.99.0:
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-
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-- provides support for ACME to make setting up Let's Encrypt certs easy, as
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- well as .well-known support.
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-
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-- does not enforce that a valid CA cert is present on the federation API, but
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- rather makes it easy to set one up.
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-
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-- provides support for .well-known
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-
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-Admins should upgrade and configure a valid CA cert. Homeservers that require a
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-.well-known entry (see below), should retain their SRV record and use it
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-alongside their .well-known record.
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-
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-**10th June 2019 - Synapse 1.0.0 is released**
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-
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-1.0.0 is scheduled for release on 10th June. In
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-accordance with the the [S2S spec](https://matrix.org/docs/spec/server_server/r0.1.0.html)
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-1.0.0 will enforce certificate validity. This means that any homeserver without a
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-valid certificate after this point will no longer be able to federate with
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-1.0.0 servers.
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-
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-## Configuring certificates for compatibility with Synapse 1.0.0
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-
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-### If you do not currently have an SRV record
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-
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-In this case, your `server_name` points to the host where your Synapse is
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-running. There is no need to create a `.well-known` URI or an SRV record, but
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-you will need to give Synapse a valid, signed, certificate.
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-
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-### If you do have an SRV record currently
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-
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-If you are using an SRV record, your matrix domain (`server_name`) may not
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-point to the same host that your Synapse is running on (the 'target
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-domain'). (If it does, you can follow the recommendation above; otherwise, read
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-on.)
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-
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-Let's assume that your `server_name` is `example.com`, and your Synapse is
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-hosted at a target domain of `customer.example.net`. Currently you should have
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-an SRV record which looks like:
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-
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-```
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-_matrix._tcp.example.com. IN SRV 10 5 8000 customer.example.net.
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-```
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-
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-In this situation, you have three choices for how to proceed:
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-
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-#### Option 1: give Synapse a certificate for your matrix domain
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-
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-Synapse 1.0 will expect your server to present a TLS certificate for your
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-`server_name` (`example.com` in the above example). You can achieve this by acquiring a
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-certificate for the `server_name` yourself (for example, using `certbot`), and giving it
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-and the key to Synapse via `tls_certificate_path` and `tls_private_key_path`.
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-
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-#### Option 2: run Synapse behind a reverse proxy
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-
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-If you have an existing reverse proxy set up with correct TLS certificates for
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-your domain, you can simply route all traffic through the reverse proxy by
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-updating the SRV record appropriately (or removing it, if the proxy listens on
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-8448).
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-
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-See [the reverse proxy documentation](reverse_proxy.md) for information on setting up a
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-reverse proxy.
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-
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-#### Option 3: add a .well-known file to delegate your matrix traffic
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-
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-This will allow you to keep Synapse on a separate domain, without having to
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-give it a certificate for the matrix domain.
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-
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-You can do this with a `.well-known` file as follows:
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-
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- 1. Keep the SRV record in place - it is needed for backwards compatibility
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- with Synapse 0.34 and earlier.
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-
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- 2. Give Synapse a certificate corresponding to the target domain
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- (`customer.example.net` in the above example). You can do this by acquire a
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- certificate for the target domain and giving it to Synapse via `tls_certificate_path`
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- and `tls_private_key_path`.
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-
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- 3. Restart Synapse to ensure the new certificate is loaded.
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-
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- 4. Arrange for a `.well-known` file at
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- `https://<server_name>/.well-known/matrix/server` with contents:
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-
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- ```json
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- {"m.server": "<target server name>"}
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- ```
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-
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- where the target server name is resolved as usual (i.e. SRV lookup, falling
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- back to talking to port 8448).
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-
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- In the above example, where synapse is listening on port 8000,
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- `https://example.com/.well-known/matrix/server` should have `m.server` set to one of:
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-
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- 1. `customer.example.net` ─ with a SRV record on
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- `_matrix._tcp.customer.example.com` pointing to port 8000, or:
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-
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- 2. `customer.example.net` ─ updating synapse to listen on the default port
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- 8448, or:
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-
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- 3. `customer.example.net:8000` ─ ensuring that if there is a reverse proxy
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- on `customer.example.net:8000` it correctly handles HTTP requests with
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- Host header set to `customer.example.net:8000`.
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-
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-## FAQ
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-
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-### Synapse 0.99.0 has just been released, what do I need to do right now?
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-
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-Upgrade as soon as you can in preparation for Synapse 1.0.0, and update your
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-TLS certificates as [above](#configuring-certificates-for-compatibility-with-synapse-100).
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-
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-### What will happen if I do not set up a valid federation certificate immediately?
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-
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-Nothing initially, but once 1.0.0 is in the wild it will not be possible to
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-federate with 1.0.0 servers.
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-
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-### What will happen if I do nothing at all?
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-
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-If the admin takes no action at all, and remains on a Synapse < 0.99.0 then the
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-homeserver will be unable to federate with those who have implemented
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-.well-known. Then, as above, once the month upgrade window has expired the
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-homeserver will not be able to federate with any Synapse >= 1.0.0
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-
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-### When do I need a SRV record or .well-known URI?
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-
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-If your homeserver listens on the default federation port (8448), and your
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-`server_name` points to the host that your homeserver runs on, you do not need an
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-SRV record or `.well-known/matrix/server` URI.
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-
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-For instance, if you registered `example.com` and pointed its DNS A record at a
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-fresh Upcloud VPS or similar, you could install Synapse 0.99 on that host,
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-giving it a server_name of `example.com`, and it would automatically generate a
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-valid TLS certificate for you via Let's Encrypt and no SRV record or
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-`.well-known` URI would be needed.
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-
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-This is the common case, although you can add an SRV record or
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-`.well-known/matrix/server` URI for completeness if you wish.
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-
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-**However**, if your server does not listen on port 8448, or if your `server_name`
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-does not point to the host that your homeserver runs on, you will need to let
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-other servers know how to find it.
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-
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-In this case, you should see ["If you do have an SRV record
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-currently"](#if-you-do-have-an-srv-record-currently) above.
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-
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-### Can I still use an SRV record?
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-
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-Firstly, if you didn't need an SRV record before (because your server is
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-listening on port 8448 of your server_name), you certainly don't need one now:
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-the defaults are still the same.
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-
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-If you previously had an SRV record, you can keep using it provided you are
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-able to give Synapse a TLS certificate corresponding to your server name. For
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-example, suppose you had the following SRV record, which directs matrix traffic
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-for example.com to matrix.example.com:443:
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-
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-```
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-_matrix._tcp.example.com. IN SRV 10 5 443 matrix.example.com
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-```
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-
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-In this case, Synapse must be given a certificate for example.com - or be
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-configured to acquire one from Let's Encrypt.
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-
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-If you are unable to give Synapse a certificate for your server_name, you will
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-also need to use a .well-known URI instead. However, see also "I have created a
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-.well-known URI. Do I still need an SRV record?".
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-
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-### I have created a .well-known URI. Do I still need an SRV record?
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-
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-As of Synapse 0.99, Synapse will first check for the existence of a `.well-known`
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-URI and follow any delegation it suggests. It will only then check for the
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-existence of an SRV record.
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-
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-That means that the SRV record will often be redundant. However, you should
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-remember that there may still be older versions of Synapse in the federation
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-which do not understand `.well-known` URIs, so if you removed your SRV record you
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-would no longer be able to federate with them.
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-
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-It is therefore best to leave the SRV record in place for now. Synapse 0.34 and
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-earlier will follow the SRV record (and not care about the invalid
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-certificate). Synapse 0.99 and later will follow the .well-known URI, with the
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-correct certificate chain.
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-
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-### It used to work just fine, why are you breaking everything?
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-
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-We have always wanted Matrix servers to be as easy to set up as possible, and
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-so back when we started federation in 2014 we didn't want admins to have to go
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-through the cumbersome process of buying a valid TLS certificate to run a
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-server. This was before Let's Encrypt came along and made getting a free and
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-valid TLS certificate straightforward. So instead, we adopted a system based on
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-[Perspectives](https://en.wikipedia.org/wiki/Convergence_(SSL)): an approach
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-where you check a set of "notary servers" (in practice, homeservers) to vouch
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-for the validity of a certificate rather than having it signed by a CA. As long
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-as enough different notaries agree on the certificate's validity, then it is
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-trusted.
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-
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-However, in practice this has never worked properly. Most people only use the
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-default notary server (matrix.org), leading to inadvertent centralisation which
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-we want to eliminate. Meanwhile, we never implemented the full consensus
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-algorithm to query the servers participating in a room to determine consensus
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-on whether a given certificate is valid. This is fiddly to get right
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-(especially in face of sybil attacks), and we found ourselves questioning
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-whether it was worth the effort to finish the work and commit to maintaining a
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-secure certificate validation system as opposed to focusing on core Matrix
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-development.
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-
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-Meanwhile, Let's Encrypt came along in 2016, and put the final nail in the
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-coffin of the Perspectives project (which was already pretty dead). So, the
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-Spec Core Team decided that a better approach would be to mandate valid TLS
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-certificates for federation alongside the rest of the Web. More details can be
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-found in
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-[MSC1711](https://github.com/matrix-org/matrix-doc/blob/main/proposals/1711-x509-for-federation.md#background-the-failure-of-the-perspectives-approach).
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-
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-This results in a breaking change, which is disruptive, but absolutely critical
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-for the security model. However, the existence of Let's Encrypt as a trivial
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-way to replace the old self-signed certificates with valid CA-signed ones helps
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-smooth things over massively, especially as Synapse can now automate Let's
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-Encrypt certificate generation if needed.
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-
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-### Can I manage my own certificates rather than having Synapse renew certificates itself?
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-
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-Yes, you are welcome to manage your certificates yourself. Synapse will only
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-attempt to obtain certificates from Let's Encrypt if you configure it to do
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-so.The only requirement is that there is a valid TLS cert present for
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-federation end points.
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-
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-### Do you still recommend against using a reverse proxy on the federation port?
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-
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-We no longer actively recommend against using a reverse proxy. Many admins will
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-find it easier to direct federation traffic to a reverse proxy and manage their
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-own TLS certificates, and this is a supported configuration.
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-
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-See [the reverse proxy documentation](reverse_proxy.md) for information on setting up a
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-reverse proxy.
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-
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-### Do I still need to give my TLS certificates to Synapse if I am using a reverse proxy?
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-
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-Practically speaking, this is no longer necessary.
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-
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-If you are using a reverse proxy for all of your TLS traffic, then you can set
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-`no_tls: True`. In that case, the only reason Synapse needs the certificate is
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-to populate a legacy 'tls_fingerprints' field in the federation API. This is
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-ignored by Synapse 0.99.0 and later, and the only time pre-0.99 Synapses will
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-check it is when attempting to fetch the server keys - and generally this is
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-delegated via `matrix.org`, which is on 0.99.0.
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-
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-However, there is a bug in Synapse 0.99.0
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-[4554](<https://github.com/matrix-org/synapse/issues/4554>) which prevents
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-Synapse from starting if you do not give it a TLS certificate. To work around
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-this, you can give it any TLS certificate at all. This will be fixed soon.
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-
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-### Do I need the same certificate for the client and federation port?
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-
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-No. There is nothing stopping you from using different certificates,
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-particularly if you are using a reverse proxy. However, Synapse will use the
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-same certificate on any ports where TLS is configured.
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-
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-### How do I tell Synapse to reload my keys/certificates after I replace them?
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-
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-Synapse will reload the keys and certificates when it receives a SIGHUP - for
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-example `kill -HUP $(cat homeserver.pid)`. Alternatively, simply restart
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-Synapse, though this will result in downtime while it restarts.
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