synapse

.. contents::

Introduction
============

Matrix is an ambitious new ecosystem for open federated Instant Messaging and
VoIP. The basics you need to know to get up and running are:

- Everything in Matrix happens in a room. Rooms are distributed and do not
exist on any single server. Rooms can be located using convenience aliases
like ``#matrix:matrix.org`` or ``#test:localhost:8448``.

- Matrix user IDs look like ``@matthew:matrix.org`` (although in the future
you will normally refer to yourself and others using a third party identifier
(3PID): email address, phone number, etc rather than manipulating Matrix user IDs)

The overall architecture is::

client <----> homeserver <=====================> homeserver <----> client
https://somewhere.org/_matrix https://elsewhere.net/_matrix

``#matrix:matrix.org`` is the official support room for Matrix, and can be
accessed by any client from https://matrix.org/docs/projects/try-matrix-now.html or
via IRC bridge at irc://irc.freenode.net/matrix.

Synapse is currently in rapid development, but as of version 0.5 we believe it
is sufficiently stable to be run as an internet-facing service for real usage!


About Matrix
============

Matrix specifies a set of pragmatic RESTful HTTP JSON APIs as an open standard,
which handle:

- Creating and managing fully distributed chat rooms with no
single points of control or failure
- Eventually-consistent cryptographically secure synchronisation of room
state across a global open network of federated servers and services
- Sending and receiving extensible messages in a room with (optional)
end-to-end encryption[1]
- Inviting, joining, leaving, kicking, banning room members
- Managing user accounts (registration, login, logout)
- Using 3rd Party IDs (3PIDs) such as email addresses, phone numbers,
Facebook accounts to authenticate, identify and discover users on Matrix.
- Placing 1:1 VoIP and Video calls

These APIs are intended to be implemented on a wide range of servers, services
and clients, letting developers build messaging and VoIP functionality on top
of the entirely open Matrix ecosystem rather than using closed or proprietary
solutions. The hope is for Matrix to act as the building blocks for a new
generation of fully open and interoperable messaging and VoIP apps for the
internet.

Synapse is a reference "homeserver" implementation of Matrix from the core
development team at matrix.org, written in Python/Twisted. It is intended to
showcase the concept of Matrix and let folks see the spec in the context of a
codebase and let you run your own homeserver and generally help bootstrap the
ecosystem.

In Matrix, every user runs one or more Matrix clients, which connect through to
a Matrix homeserver. The homeserver stores all their personal chat history and
user account information - much as a mail client connects through to an
IMAP/SMTP server. Just like email, you can either run your own Matrix
homeserver and control and own your own communications and history or use one
hosted by someone else (e.g. matrix.org) - there is no single point of control
or mandatory service provider in Matrix, unlike WhatsApp, Facebook, Hangouts,
etc.

We'd like to invite you to join #matrix:matrix.org (via
https://matrix.org/docs/projects/try-matrix-now.html), run a homeserver, take a look
at the `Matrix spec `_, and experiment with the
`APIs `_ and `Client SDKs
`_.

Thanks for using Matrix!

[1] End-to-end encryption is currently in beta: `blog post `_.


Synapse Installation
====================

Synapse is the reference Python/Twisted Matrix homeserver implementation.

System requirements:

- POSIX-compliant system (tested on Linux & OS X)
- Python 2.7
- At least 1GB of free RAM if you want to join large public rooms like #matrix:matrix.org

Installing from source
----------------------

(Prebuilt packages are available for some platforms - see `Platform-Specific
Instructions`_.)

Synapse is written in Python but some of the libraries it uses are written in
C. So before we can install Synapse itself we need a working C compiler and the
header files for Python C extensions.

Installing prerequisites on Ubuntu or Debian::

sudo apt-get install build-essential python2.7-dev libffi-dev \
python-pip python-setuptools sqlite3 \
libssl-dev python-virtualenv libjpeg-dev libxslt1-dev

Installing prerequisites on ArchLinux::

sudo pacman -S base-devel python2 python-pip \
python-setuptools python-virtualenv sqlite3

Installing prerequisites on CentOS 7 or Fedora 25::

sudo yum install libtiff-devel libjpeg-devel libzip-devel freetype-devel \
lcms2-devel libwebp-devel tcl-devel tk-devel redhat-rpm-config \
python-virtualenv libffi-devel openssl-devel
sudo yum groupinstall "Development Tools"

Installing prerequisites on Mac OS X::

xcode-select --install
sudo easy_install pip
sudo pip install virtualenv
brew install pkg-config libffi

Installing prerequisites on Raspbian::

sudo apt-get install build-essential python2.7-dev libffi-dev \
python-pip python-setuptools sqlite3 \
libssl-dev python-virtualenv libjpeg-dev
sudo pip install --upgrade pip
sudo pip install --upgrade ndg-httpsclient
sudo pip install --upgrade virtualenv

Installing prerequisites on openSUSE::

sudo zypper in -t pattern devel_basis
sudo zypper in python-pip python-setuptools sqlite3 python-virtualenv \
python-devel libffi-devel libopenssl-devel libjpeg62-devel

Installing prerequisites on OpenBSD::

doas pkg_add python libffi py-pip py-setuptools sqlite3 py-virtualenv \
libxslt jpeg

To install the Synapse homeserver run::

virtualenv -p python2.7 ~/.synapse
source ~/.synapse/bin/activate
pip install --upgrade pip
pip install --upgrade setuptools
pip install matrix-synapse

This installs Synapse, along with the libraries it uses, into a virtual
environment under ``~/.synapse``. Feel free to pick a different directory
if you prefer.

This Synapse installation can then be later upgraded by using pip again with the
update flag::

source ~/.synapse/bin/activate
pip install -U matrix-synapse

In case of problems, please see the _`Troubleshooting` section below.

There is an offical synapse image available at
https://hub.docker.com/r/matrixdotorg/synapse/tags/ which can be used with
the docker-compose file available at `contrib/docker `_. Further information on
this including configuration options is available in the README on
hub.docker.com.

Alternatively, Andreas Peters (previously Silvio Fricke) has contributed a
Dockerfile to automate a synapse server in a single Docker image, at
https://hub.docker.com/r/avhost/docker-matrix/tags/

Slavi Pantaleev has created an Ansible playbook,
which installs the offical Docker image of Matrix Synapse
along with many other Matrix-related services (Postgres database, riot-web, coturn, mxisd, SSL support, etc.).
For more details, see
https://github.com/spantaleev/matrix-docker-ansible-deploy

Configuring Synapse
-------------------

Before you can start Synapse, you will need to generate a configuration
file. To do this, run (in your virtualenv, as before)::

cd ~/.synapse
python -m synapse.app.homeserver \
--server-name my.domain.name \
--config-path homeserver.yaml \
--generate-config \
--report-stats=[yes|no]

... substituting an appropriate value for ``--server-name``. The server name
determines the "domain" part of user-ids for users on your server: these will
all be of the format ``@user:my.domain.name``. It also determines how other
matrix servers will reach yours for `Federation`_. For a test configuration,
set this to the hostname of your server. For a more production-ready setup, you
will probably want to specify your domain (``example.com``) rather than a
matrix-specific hostname here (in the same way that your email address is
probably ``user@example.com`` rather than ``user@email.example.com``) - but
doing so may require more advanced setup - see `Setting up
Federation`_. Beware that the server name cannot be changed later.

This command will generate you a config file that you can then customise, but it will
also generate a set of keys for you. These keys will allow your Home Server to
identify itself to other Home Servers, so don't lose or delete them. It would be
wise to back them up somewhere safe. (If, for whatever reason, you do need to
change your Home Server's keys, you may find that other Home Servers have the
old key cached. If you update the signing key, you should change the name of the
key in the ``.signing.key`` file (the second word) to something
different. See `the spec`__ for more information on key management.)

.. __: `key_management`_

The default configuration exposes two HTTP ports: 8008 and 8448. Port 8008 is
configured without TLS; it should be behind a reverse proxy for TLS/SSL
termination on port 443 which in turn should be used for clients. Port 8448
is configured to use TLS with a self-signed certificate. If you would like
to do initial test with a client without having to setup a reverse proxy,
you can temporarly use another certificate. (Note that a self-signed
certificate is fine for `Federation`_). You can do so by changing
``tls_certificate_path``, ``tls_private_key_path`` and ``tls_dh_params_path``
in ``homeserver.yaml``; alternatively, you can use a reverse-proxy, but be sure
to read `Using a reverse proxy with Synapse`_ when doing so.

Apart from port 8448 using TLS, both ports are the same in the default
configuration.

Registering a user
------------------

You will need at least one user on your server in order to use a Matrix
client. Users can be registered either `via a Matrix client`__, or via a
commandline script.

.. __: `client-user-reg`_

To get started, it is easiest to use the command line to register new users::

$ source ~/.synapse/bin/activate
$ synctl start # if not already running
$ register_new_matrix_user -c homeserver.yaml https://localhost:8448
New user localpart: erikj
Password:
Confirm password:
Make admin [no]:
Success!

This process uses a setting ``registration_shared_secret`` in
``homeserver.yaml``, which is shared between Synapse itself and the
``register_new_matrix_user`` script. It doesn't matter what it is (a random
value is generated by ``--generate-config``), but it should be kept secret, as
anyone with knowledge of it can register users on your server even if
``enable_registration`` is ``false``.

Setting up a TURN server
------------------------

For reliable VoIP calls to be routed via this homeserver, you MUST configure
a TURN server. See ``_ for details.

Running Synapse
===============

To actually run your new homeserver, pick a working directory for Synapse to
run (e.g. ``~/.synapse``), and::

cd ~/.synapse
source ./bin/activate
synctl start


Connecting to Synapse from a client
===================================

The easiest way to try out your new Synapse installation is by connecting to it
from a web client. The easiest option is probably the one at
https://riot.im/app. You will need to specify a "Custom server" when you log on
or register: set this to ``https://domain.tld`` if you setup a reverse proxy
following the recommended setup, or ``https://localhost:8448`` - remember to specify the
port (``:8448``) if not ``:443`` unless you changed the configuration. (Leave the identity
server as the default - see `Identity servers`_.)

If using port 8448 you will run into errors until you accept the self-signed
certificate. You can easily do this by going to ``https://localhost:8448``
directly with your browser and accept the presented certificate. You can then
go back in your web client and proceed further.

If all goes well you should at least be able to log in, create a room, and
start sending messages.

(The homeserver runs a web client by default at https://localhost:8448/, though
as of the time of writing it is somewhat outdated and not really recommended -
https://github.com/matrix-org/synapse/issues/1527).

.. _`client-user-reg`:

Registering a new user from a client
------------------------------------

By default, registration of new users via Matrix clients is disabled. To enable
it, specify ``enable_registration: true`` in ``homeserver.yaml``. (It is then
recommended to also set up CAPTCHA - see ``_.)

Once ``enable_registration`` is set to ``true``, it is possible to register a
user via `riot.im `_ or other Matrix clients.

Your new user name will be formed partly from the ``server_name`` (see
`Configuring synapse`_), and partly from a localpart you specify when you
create the account. Your name will take the form of::

@localpart:my.domain.name

(pronounced "at localpart on my dot domain dot name").

As when logging in, you will need to specify a "Custom server". Specify your
desired ``localpart`` in the 'User name' box.


Security Note
=============

Matrix serves raw user generated data in some APIs - specifically the `content
repository endpoints `_.

Whilst we have tried to mitigate against possible XSS attacks (e.g.
https://github.com/matrix-org/synapse/pull/1021) we recommend running
matrix homeservers on a dedicated domain name, to limit any malicious user generated
content served to web browsers a matrix API from being able to attack webapps hosted
on the same domain. This is particularly true of sharing a matrix webclient and
server on the same domain.

See https://github.com/vector-im/vector-web/issues/1977 and
https://developer.github.com/changes/2014-04-25-user-content-security for more details.


Platform-Specific Instructions
==============================

Debian
------

Matrix provides official Debian packages via apt from https://matrix.org/packages/debian/.
Note that these packages do not include a client - choose one from
https://matrix.org/docs/projects/try-matrix-now.html (or build your own with one of our SDKs :)

Fedora
------

Synapse is in the Fedora repositories as ``matrix-synapse``::

sudo dnf install matrix-synapse

Oleg Girko provides Fedora RPMs at
https://obs.infoserver.lv/project/monitor/matrix-synapse

OpenSUSE
--------

Synapse is in the OpenSUSE repositories as ``matrix-synapse``::

sudo zypper install matrix-synapse

SUSE Linux Enterprise Server
----------------------------

Unofficial package are built for SLES 15 in the openSUSE:Backports:SLE-15 repository at
https://download.opensuse.org/repositories/openSUSE:/Backports:/SLE-15/standard/

ArchLinux
---------

The quickest way to get up and running with ArchLinux is probably with the community package
https://www.archlinux.org/packages/community/any/matrix-synapse/, which should pull in most of
the necessary dependencies. If the default web client is to be served (enabled by default in
the generated config),
https://www.archlinux.org/packages/community/any/python2-matrix-angular-sdk/ will also need to
be installed.

Alternatively, to install using pip a few changes may be needed as ArchLinux
defaults to python 3, but synapse currently assumes python 2.7 by default:

pip may be outdated (6.0.7-1 and needs to be upgraded to 6.0.8-1 )::

sudo pip2.7 install --upgrade pip

You also may need to explicitly specify python 2.7 again during the install
request::

pip2.7 install https://github.com/matrix-org/synapse/tarball/master

If you encounter an error with lib bcrypt causing an Wrong ELF Class:
ELFCLASS32 (x64 Systems), you may need to reinstall py-bcrypt to correctly
compile it under the right architecture. (This should not be needed if
installing under virtualenv)::

sudo pip2.7 uninstall py-bcrypt
sudo pip2.7 install py-bcrypt

During setup of Synapse you need to call python2.7 directly again::

cd ~/.synapse
python2.7 -m synapse.app.homeserver \
--server-name machine.my.domain.name \
--config-path homeserver.yaml \
--generate-config

...substituting your host and domain name as appropriate.

FreeBSD
-------

Synapse can be installed via FreeBSD Ports or Packages contributed by Brendan Molloy from:

- Ports: ``cd /usr/ports/net-im/py-matrix-synapse && make install clean``
- Packages: ``pkg install py27-matrix-synapse``


OpenBSD
-------

There is currently no port for OpenBSD. Additionally, OpenBSD's security
settings require a slightly more difficult installation process.

1) Create a new directory in ``/usr/local`` called ``_synapse``. Also, create a
new user called ``_synapse`` and set that directory as the new user's home.
This is required because, by default, OpenBSD only allows binaries which need
write and execute permissions on the same memory space to be run from
``/usr/local``.
2) ``su`` to the new ``_synapse`` user and change to their home directory.
3) Create a new virtualenv: ``virtualenv -p python2.7 ~/.synapse``
4) Source the virtualenv configuration located at
``/usr/local/_synapse/.synapse/bin/activate``. This is done in ``ksh`` by
using the ``.`` command, rather than ``bash``'s ``source``.
5) Optionally, use ``pip`` to install ``lxml``, which Synapse needs to parse
webpages for their titles.
6) Use ``pip`` to install this repository: ``pip install matrix-synapse``
7) Optionally, change ``_synapse``'s shell to ``/bin/false`` to reduce the
chance of a compromised Synapse server being used to take over your box.

After this, you may proceed with the rest of the install directions.

NixOS
-----

Robin Lambertz has packaged Synapse for NixOS at:
https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/misc/matrix-synapse.nix

Windows Install
---------------

If you wish to run or develop Synapse on Windows, the Windows Subsystem For
Linux provides a Linux environment on Windows 10 which is capable of using the
Debian, Fedora, or source installation methods. More information about WSL can
be found at https://docs.microsoft.com/en-us/windows/wsl/install-win10 for
Windows 10 and https://docs.microsoft.com/en-us/windows/wsl/install-on-server
for Windows Server.

Troubleshooting
===============

Troubleshooting Installation
----------------------------

Synapse requires pip 8 or later, so if your OS provides too old a version you
may need to manually upgrade it::

sudo pip install --upgrade pip

Installing may fail with ``Could not find any downloads that satisfy the requirement pymacaroons-pynacl (from matrix-synapse==0.12.0)``.
You can fix this by manually upgrading pip and virtualenv::

sudo pip install --upgrade virtualenv

You can next rerun ``virtualenv -p python2.7 synapse`` to update the virtual env.

Installing may fail during installing virtualenv with ``InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#insecureplatformwarning.``
You can fix this by manually installing ndg-httpsclient::

pip install --upgrade ndg-httpsclient

Installing may fail with ``mock requires setuptools>=17.1. Aborting installation``.
You can fix this by upgrading setuptools::

pip install --upgrade setuptools

If pip crashes mid-installation for reason (e.g. lost terminal), pip may
refuse to run until you remove the temporary installation directory it
created. To reset the installation::

rm -rf /tmp/pip_install_matrix

pip seems to leak *lots* of memory during installation. For instance, a Linux
host with 512MB of RAM may run out of memory whilst installing Twisted. If this
happens, you will have to individually install the dependencies which are
failing, e.g.::

pip install twisted

Running out of File Handles
~~~~~~~~~~~~~~~~~~~~~~~~~~~

If synapse runs out of filehandles, it typically fails badly - live-locking
at 100% CPU, and/or failing to accept new TCP connections (blocking the
connecting client). Matrix currently can legitimately use a lot of file handles,
thanks to busy rooms like #matrix:matrix.org containing hundreds of participating
servers. The first time a server talks in a room it will try to connect
simultaneously to all participating servers, which could exhaust the available
file descriptors between DNS queries & HTTPS sockets, especially if DNS is slow
to respond. (We need to improve the routing algorithm used to be better than
full mesh, but as of June 2017 this hasn't happened yet).

If you hit this failure mode, we recommend increasing the maximum number of
open file handles to be at least 4096 (assuming a default of 1024 or 256).
This is typically done by editing ``/etc/security/limits.conf``

Separately, Synapse may leak file handles if inbound HTTP requests get stuck
during processing - e.g. blocked behind a lock or talking to a remote server etc.
This is best diagnosed by matching up the 'Received request' and 'Processed request'
log lines and looking for any 'Processed request' lines which take more than
a few seconds to execute. Please let us know at #matrix-dev:matrix.org if
you see this failure mode so we can help debug it, however.

ArchLinux
~~~~~~~~~

If running `$ synctl start` fails with 'returned non-zero exit status 1',
you will need to explicitly call Python2.7 - either running as::

python2.7 -m synapse.app.homeserver --daemonize -c homeserver.yaml

...or by editing synctl with the correct python executable.


Upgrading an existing Synapse
=============================

The instructions for upgrading synapse are in `UPGRADE.rst`_.
Please check these instructions as upgrading may require extra steps for some
versions of synapse.

.. _UPGRADE.rst: UPGRADE.rst

.. _federation:

Setting up Federation
=====================

Federation is the process by which users on different servers can participate
in the same room. For this to work, those other servers must be able to contact
yours to send messages.

As explained in `Configuring synapse`_, the ``server_name`` in your
``homeserver.yaml`` file determines the way that other servers will reach
yours. By default, they will treat it as a hostname and try to connect to
port 8448. This is easy to set up and will work with the default configuration,
provided you set the ``server_name`` to match your machine's public DNS
hostname.

For a more flexible configuration, you can set up a DNS SRV record. This allows
you to run your server on a machine that might not have the same name as your
domain name. For example, you might want to run your server at
``synapse.example.com``, but have your Matrix user-ids look like
``@user:example.com``. (A SRV record also allows you to change the port from
the default 8448. However, if you are thinking of using a reverse-proxy on the
federation port, which is not recommended, be sure to read
`Reverse-proxying the federation port`_ first.)

To use a SRV record, first create your SRV record and publish it in DNS. This
should have the format ``_matrix._tcp. IN SRV 10 0
``. The DNS record should then look something like::

$ dig -t srv _matrix._tcp.example.com
_matrix._tcp.example.com. 3600 IN SRV 10 0 8448 synapse.example.com.

Note that the server hostname cannot be an alias (CNAME record): it has to point
directly to the server hosting the synapse instance.

You can then configure your homeserver to use ```` as the domain in
its user-ids, by setting ``server_name``::

python -m synapse.app.homeserver \
--server-name \
--config-path homeserver.yaml \
--generate-config
python -m synapse.app.homeserver --config-path homeserver.yaml

If you've already generated the config file, you need to edit the ``server_name``
in your ``homeserver.yaml`` file. If you've already started Synapse and a
database has been created, you will have to recreate the database.

If all goes well, you should be able to `connect to your server with a client`__,
and then join a room via federation. (Try ``#matrix-dev:matrix.org`` as a first
step. "Matrix HQ"'s sheer size and activity level tends to make even the
largest boxes pause for thought.)

.. __: `Connecting to Synapse from a client`_

Troubleshooting
---------------

You can use the federation tester to check if your homeserver is all set:
``https://matrix.org/federationtester/api/report?server_name=``
If any of the attributes under "checks" is false, federation won't work.

The typical failure mode with federation is that when you try to join a room,
it is rejected with "401: Unauthorized". Generally this means that other
servers in the room couldn't access yours. (Joining a room over federation is a
complicated dance which requires connections in both directions).

So, things to check are:

* If you are trying to use a reverse-proxy, read `Reverse-proxying the
federation port`_.
* If you are not using a SRV record, check that your ``server_name`` (the part
of your user-id after the ``:``) matches your hostname, and that port 8448 on
that hostname is reachable from outside your network.
* If you *are* using a SRV record, check that it matches your ``server_name``
(it should be ``_matrix._tcp.``), and that the port and hostname
it specifies are reachable from outside your network.

Running a Demo Federation of Synapses
-------------------------------------

If you want to get up and running quickly with a trio of homeservers in a
private federation, there is a script in the ``demo`` directory. This is mainly
useful just for development purposes. See ``_.


Using PostgreSQL
================

As of Synapse 0.9, `PostgreSQL `_ is supported as an
alternative to the `SQLite `_ database that Synapse has
traditionally used for convenience and simplicity.

The advantages of Postgres include:

* significant performance improvements due to the superior threading and
caching model, smarter query optimiser
* allowing the DB to be run on separate hardware
* allowing basic active/backup high-availability with a "hot spare" synapse
pointing at the same DB master, as well as enabling DB replication in
synapse itself.

For information on how to install and use PostgreSQL, please see
`docs/postgres.rst `_.


.. _reverse-proxy:

Using a reverse proxy with Synapse
==================================

It is recommended to put a reverse proxy such as
`nginx `_,
`Apache `_,
`Caddy `_ or
`HAProxy `_ 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.

The most important thing to know here is that Matrix clients and other Matrix
servers do not necessarily need to connect to your server via the same
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'.

The next most important thing to know is that using a reverse-proxy on the
federation port has a number of pitfalls. It is possible, but be sure to read
`Reverse-proxying the federation port`_.

The recommended setup is therefore to configure your reverse-proxy on port 443
to port 8008 of synapse for client connections, but to also directly expose port
8448 for server-server connections. All the Matrix endpoints begin ``/_matrix``,
so an example nginx configuration might look like::

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;
}
}

an example Caddy configuration might look like::

matrix.example.com {
proxy /_matrix http://localhost:8008 {
transparent
}
}

and an example Apache configuration might look like::


SSLEngine on
ServerName matrix.example.com;


ProxyPass http://127.0.0.1:8008/_matrix nocanon
ProxyPassReverse http://127.0.0.1:8008/_matrix



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`_.

Reverse-proxying the federation port
------------------------------------

There are two issues to consider before using a reverse-proxy on the federation
port:

* Due to the way SSL certificates are managed in the Matrix federation protocol
(see `spec`__), Synapse needs to be configured with the path to the SSL
certificate, *even if you do not terminate SSL at Synapse*.

.. __: `key_management`_

* Until v0.33.3, Synapse did not support SNI on the federation port
(`bug #1491 `_). This bug
is now fixed, but means that federating with older servers can be unreliable
when using name-based virtual hosting.

Furthermore, a number of the normal reasons for using a reverse-proxy do not
apply:

* Other servers will connect on port 8448 by default, so there is no need to
listen on port 443 (for federation, at least), which avoids the need for root
privileges and virtual hosting.

* A self-signed SSL certificate is fine for federation, so there is no need to
automate renewals. (The certificate generated by ``--generate-config`` is
valid for 10 years.)

If you want to set up a reverse-proxy on the federation port despite these
caveats, you will need to do the following:

* In ``homeserver.yaml``, set ``tls_certificate_path`` to the path to the SSL
certificate file used by your reverse-proxy, and set ``no_tls`` to ``True``.
(``tls_private_key_path`` will be ignored if ``no_tls`` is ``True``.)

* In your reverse-proxy configuration:

* If there are other virtual hosts on the same port, make sure that the
*default* one uses the certificate configured above.

* Forward ``/_matrix`` to Synapse.

* If your reverse-proxy is not listening on port 8448, publish a SRV record to
tell other servers how to find you. See `Setting up Federation`_.

When updating the SSL certificate, just update the file pointed to by
``tls_certificate_path``: there is no need to restart synapse. (You may like to
use a symbolic link to help make this process atomic.)

The most common mistake when setting up federation is not to tell Synapse about
your SSL certificate. To check it, you can visit
``https://matrix.org/federationtester/api/report?server_name=``.
Unfortunately, there is no UI for this yet, but, you should see
``"MatchingTLSFingerprint": true``. If not, check that
``Certificates[0].SHA256Fingerprint`` (the fingerprint of the certificate
presented by your reverse-proxy) matches ``Keys.tls_fingerprints[0].sha256``
(the fingerprint of the certificate Synapse is using).


Identity Servers
================

Identity servers have the job of mapping email addresses and other 3rd Party
IDs (3PIDs) to Matrix user IDs, as well as verifying the ownership of 3PIDs
before creating that mapping.

**They are not where accounts or credentials are stored - these live on home
servers. Identity Servers are just for mapping 3rd party IDs to matrix IDs.**

This process is very security-sensitive, as there is obvious risk of spam if it
is too easy to sign up for Matrix accounts or harvest 3PID data. In the longer
term, we hope to create a decentralised system to manage it (`matrix-doc #712
`_), but in the meantime,
the role of managing trusted identity in the Matrix ecosystem is farmed out to
a cluster of known trusted ecosystem partners, who run 'Matrix Identity
Servers' such as `Sydent `_, whose role
is purely to authenticate and track 3PID logins and publish end-user public
keys.

You can host your own copy of Sydent, but this will prevent you reaching other
users in the Matrix ecosystem via their email address, and prevent them finding
you. We therefore recommend that you use one of the centralised identity servers
at ``https://matrix.org`` or ``https://vector.im`` for now.

To reiterate: the Identity server will only be used if you choose to associate
an email address with your account, or send an invite to another user via their
email address.


URL Previews
============

Synapse 0.15.0 introduces a new API for previewing URLs at
``/_matrix/media/r0/preview_url``. This is disabled by default. To turn it on
you must enable the ``url_preview_enabled: True`` config parameter and
explicitly specify the IP ranges that Synapse is not allowed to spider for
previewing in the ``url_preview_ip_range_blacklist`` configuration parameter.
This is critical from a security perspective to stop arbitrary Matrix users
spidering 'internal' URLs on your network. At the very least we recommend that
your loopback and RFC1918 IP addresses are blacklisted.

This also requires the optional lxml and netaddr python dependencies to be
installed. This in turn requires the libxml2 library to be available - on
Debian/Ubuntu this means ``apt-get install libxml2-dev``, or equivalent for
your OS.


Password reset
==============

If a user has registered an email address to their account using an identity
server, they can request a password-reset token via clients such as Vector.

A manual password reset can be done via direct database access as follows.

First calculate the hash of the new password::

$ source ~/.synapse/bin/activate
$ ./scripts/hash_password
Password:
Confirm password:
$2a$12$xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Then update the `users` table in the database::

UPDATE users SET password_hash='$2a$12$xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
WHERE name='@test:test.com';


Synapse Development
===================

Before setting up a development environment for synapse, make sure you have the
system dependencies (such as the python header files) installed - see
`Installing from source`_.

To check out a synapse for development, clone the git repo into a working
directory of your choice::

git clone https://github.com/matrix-org/synapse.git
cd synapse

Synapse has a number of external dependencies, that are easiest
to install using pip and a virtualenv::

virtualenv -p python2.7 env
source env/bin/activate
python -m synapse.python_dependencies | xargs pip install
pip install lxml mock

This will run a process of downloading and installing all the needed
dependencies into a virtual env.

Once this is done, you may wish to run Synapse's unit tests, to
check that everything is installed as it should be::

PYTHONPATH="." trial tests

This should end with a 'PASSED' result::

Ran 143 tests in 0.601s

PASSED (successes=143)

Running the Integration Tests
=============================

Synapse is accompanied by `SyTest `_,
a Matrix homeserver integration testing suite, which uses HTTP requests to
access the API as a Matrix client would. It is able to run Synapse directly from
the source tree, so installation of the server is not required.

Testing with SyTest is recommended for verifying that changes related to the
Client-Server API are functioning correctly. See the `installation instructions
`_ for details.

Building Internal API Documentation
===================================

Before building internal API documentation install sphinx and
sphinxcontrib-napoleon::

pip install sphinx
pip install sphinxcontrib-napoleon

Building internal API documentation::

python setup.py build_sphinx


Help!! Synapse eats all my RAM!
===============================

Synapse's architecture is quite RAM hungry currently - we deliberately
cache a lot of recent room data and metadata in RAM in order to speed up
common requests. We'll improve this in future, but for now the easiest
way to either reduce the RAM usage (at the risk of slowing things down)
is to set the almost-undocumented ``SYNAPSE_CACHE_FACTOR`` environment
variable. The default is 0.5, which can be decreased to reduce RAM usage
in memory constrained enviroments, or increased if performance starts to
degrade.

Using `libjemalloc `_ can also yield a significant
improvement in overall amount, and especially in terms of giving back RAM
to the OS. To use it, the library must simply be put in the LD_PRELOAD
environment variable when launching Synapse. On Debian, this can be done
by installing the ``libjemalloc1`` package and adding this line to
``/etc/default/matrix-synapse``::

LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.1

.. _`key_management`: https://matrix.org/docs/spec/server_server/unstable.html#retrieving-server-keys