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

For details on how to install synapse, see INSTALL.md.

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.

Unless you are running a test instance of Synapse on your local machine, in general, you will need to enable TLS support before you can successfully connect from a client: see INSTALL.md#tls-certificates.

An easy way to get started is to login or register via Riot at https://riot.im/app/#/login or https://riot.im/app/#/register respectively. You will need to change the server you are logging into from matrix.org and instead specify a Homeserver URL of https://<server_name>:8448 (or just https://<server_name> if you are using a reverse proxy). (Leave the identity server as the default - see Identity servers.) If you prefer to use another client, refer to our client breakdown.

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

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 docs/CAPTCHA_SETUP.rst.)

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.

ACME setup

For details on having Synapse manage your federation TLS certificates automatically, please see docs/ACME.md.

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

Troubleshooting

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 #synapse:matrix.org if you see this failure mode so we can help debug it, however.

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

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.

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.

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, and give Synapse a TLS certificate which is valid for your server_name.

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).

To use a SRV record, first create your SRV record and publish it in DNS. This should have the format _matrix._tcp.<yourdomain.com> <ttl> IN SRV 10 0 <port> <synapse.server.name>. 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 <yourdomain.com> as the domain in its user-ids, by setting server_name:

python -m synapse.app.homeserver \
    --server-name <yourdomain.com> \
    --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.)

Troubleshooting

You can use the federation tester to check if your homeserver is all set.

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 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.<server_name>), and that the port and hostname it specifies are reachable from outside your network.

Another common problem is that people on other servers can't join rooms that you invite them to. This can be caused by an incorrectly-configured reverse proxy: see docs/reverse_proxy.rst for instructions on how to correctly configure a reverse proxy.

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 demo/README.

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.

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.

For information on configuring one, see docs/reverse_proxy.rst.

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.

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 Riot.

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

First calculate the hash of the new password:

$ ~/synapse/env/bin/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 python3 env
source env/bin/activate
python -m pip install -e .[all]

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:

python -m twisted.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