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Introduction

sygnal is a reference Push Gateway for Matrix (http://matrix.org/).

See http://matrix.org/docs/spec/client_server/r0.2.0.html#id51 for a high level overview of how notifications work in Matrix.

http://matrix.org/docs/spec/push_gateway/unstable.html#post-matrix-push-r0-notify describes the protocol that Matrix Home Servers use to send notifications to Push Gateways such as sygnal.

Setup

sygnal is a plain WSGI app, although these instructions use gunicorn which will create a complete, standalone webserver. When used with gunicorn, sygnal can use gunicorn's extra hook to perform a clean shutdown which tries as hard as possible to ensure no messages are lost.

There are two config files:
  • sygnal.cfg (The app-specific config file)
  • gunicorn_config.py (gunicorn's config file)

sygnal.cfg contains configuration for sygnal itself. This includes the location and level of sygnal's log file. The [apps] section is where you set up different apps that are to be handled. Keys in this section take the form of the app_id and the name of the configuration key, joined by a single dot ('.'). The app_id is as specified when setting up a Matrix pusher (see http://matrix.org/docs/spec/client_server/r0.2.0.html#post-matrix-client-r0-pushers-set). So for example, the type for the App ID of com.example.myapp.ios.prod would be specified as follows:

com.example.myapp.ios.prod.type = foobar

The gunicorn sample config contains everything necessary to run sygnal from gunicorn. The shutdown hook handles clean shutdown. You can customise other aspects of this file as you wish to change, for example, the log location or the bind port.

Note that sygnal uses gevent. You should therefore not change the worker class or the number of workers (which should be 1: in gevent, a single worker uses multiple greenlets to handle all the requests).

App Types

There are two supported App Types:

apns
This sends push notifications to iOS apps via the Apple Push Notification Service (APNS). It expects the 'certfile' parameter to be a path relative to sygnal's working directory of a PEM file containing the APNS certificate and unencrypted private key.
gcm
This sends messages via Google Cloud Messaging (GCM) and hence can be used to deliver notifications to Android apps. It expects the 'apiKey' parameter to contain the secret GCM key.

Running

To run with gunicorn:

gunicorn -c gunicorn_config.py sygnal:app

You can customise the gunicorn_config.py to determine whether this daemonizes or runs in the foreground.

Gunicorn maintains its own logging in addition to the app's, so the access_log and error_log contain gunicorn's accesses and gunicorn specific errors. The log file in sygnal.cfg contains app level logging.

Clean shutdown

The code for APNS uses a grace period where it waits for errors to come down the socket before declaring it safe for the app to shut down (due to the design of APNS). Terminating using SIGTERM performs a clean shutdown:

kill -TERM `cat sygnal.pid`

Restarting sygnal using SIGHUP will handle this gracefully:

kill -HUP `cat sygnal.pid`

Log Rotation

Gunicorn appends to files but does not use a rotating logger. Sygnal's app logging does the same. Gunicorn will re-open all log files (including the app's) when sent SIGUSR1. The recommended configuration is therefore to use logrotate.