336 lines
15 KiB
Markdown
336 lines
15 KiB
Markdown
# MSC1711 Certificates FAQ
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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/master/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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Much of what follows is now outdated since most admins will have already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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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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## 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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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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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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**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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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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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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## Contents
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* Timeline
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* Configuring certificates for compatibility with Synapse 1.0
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* FAQ
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* Synapse 0.99.0 has just been released, what do I need to do right now?
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* How do I upgrade?
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* What will happen if I do not set up a valid federation certificate
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immediately?
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* What will happen if I do nothing at all?
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* When do I need a SRV record or .well-known URI?
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* Can I still use an SRV record?
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* I have created a .well-known URI. Do I still need an SRV record?
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* It used to work just fine, why are you breaking everything?
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* Can I manage my own certificates rather than having Synapse renew
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certificates itself?
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* Do you still recommend against using a reverse proxy on the federation port?
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* Do I still need to give my TLS certificates to Synapse if I am using a
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reverse proxy?
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* Do I need the same certificate for the client and federation port?
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* How do I tell Synapse to reload my keys/certificates after I replace them?
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## Timeline
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**5th Feb 2019 - Synapse 0.99.0 is released.**
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All server admins are encouraged to upgrade.
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0.99.0:
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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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- 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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- provides support for .well-known
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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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**10th June 2019 - Synapse 1.0.0 is released**
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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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## Configuring certificates for compatibility with Synapse 1.0.0
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### If you do not currently have an SRV record
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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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### If you do have an SRV record currently
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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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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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_matrix._tcp.example.com. IN SRV 10 5 8000 customer.example.net.
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```
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In this situation, you have three choices for how to proceed:
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#### Option 1: give Synapse a certificate for your matrix domain
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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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#### Option 2: run Synapse behind a reverse proxy
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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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See [the reverse proxy documentation](reverse_proxy.md) for information on setting up a
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reverse proxy.
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#### Option 3: add a .well-known file to delegate your matrix traffic
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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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You can do this with a `.well-known` file as follows:
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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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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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3. Restart Synapse to ensure the new certificate is loaded.
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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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```json
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{"m.server": "<target server name>"}
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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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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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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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2. `customer.example.net` ─ updating synapse to listen on the default port
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8448, or:
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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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## FAQ
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### Synapse 0.99.0 has just been released, what do I need to do right now?
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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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### What will happen if I do not set up a valid federation certificate immediately?
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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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### What will happen if I do nothing at all?
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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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### When do I need a SRV record or .well-known URI?
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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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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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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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**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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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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### Can I still use an SRV record?
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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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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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_matrix._tcp.example.com. IN SRV 10 5 443 matrix.example.com
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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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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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### I have created a .well-known URI. Do I still need an SRV record?
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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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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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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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### It used to work just fine, why are you breaking everything?
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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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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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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/master/proposals/1711-x509-for-federation.md#background-the-failure-of-the-perspectives-approach).
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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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### Can I manage my own certificates rather than having Synapse renew certificates itself?
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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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### Do you still recommend against using a reverse proxy on the federation port?
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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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See [the reverse proxy documentation](reverse_proxy.md) for information on setting up a
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reverse proxy.
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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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Practically speaking, this is no longer necessary.
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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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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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### Do I need the same certificate for the client and federation port?
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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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### How do I tell Synapse to reload my keys/certificates after I replace them?
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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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