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diff --git a/docs/workers.md b/docs/workers.md index 38bd758e57..bfec745897 100644 --- a/docs/workers.md +++ b/docs/workers.md @@ -1,10 +1,10 @@ # Scaling synapse via workers -For small instances it recommended to run Synapse in monolith mode (the -default). For larger instances where performance is a concern it can be helpful -to split out functionality into multiple separate python processes. These -processes are called 'workers', and are (eventually) intended to scale -horizontally independently. +For small instances it recommended to run Synapse in the default monolith mode. +For larger instances where performance is a concern it can be helpful to split +out functionality into multiple separate python processes. These processes are +called 'workers', and are (eventually) intended to scale horizontally +independently. Synapse's worker support is under active development and subject to change as we attempt to rapidly scale ever larger Synapse instances. However we are @@ -23,29 +23,30 @@ The processes communicate with each other via a Synapse-specific protocol called feeds streams of newly written data between processes so they can be kept in sync with the database state. -Additionally, processes may make HTTP requests to each other. Typically this is -used for operations which need to wait for a reply - such as sending an event. +When configured to do so, Synapse uses a +[Redis pub/sub channel](https://redis.io/topics/pubsub) to send the replication +stream between all configured Synapse processes. Additionally, processes may +make HTTP requests to each other, primarily for operations which need to wait +for a reply ─ such as sending an event. -As of Synapse v1.13.0, it is possible to configure Synapse to send replication -via a [Redis pub/sub channel](https://redis.io/topics/pubsub), and is now the -recommended way of configuring replication. This is an alternative to the old -direct TCP connections to the main process: rather than all the workers -connecting to the main process, all the workers and the main process connect to -Redis, which relays replication commands between processes. This can give a -significant cpu saving on the main process and will be a prerequisite for -upcoming performance improvements. +Redis support was added in v1.13.0 with it becoming the recommended method in +v1.18.0. It replaced the old direct TCP connections (which is deprecated as of +v1.18.0) to the main process. With Redis, rather than all the workers connecting +to the main process, all the workers and the main process connect to Redis, +which relays replication commands between processes. This can give a significant +cpu saving on the main process and will be a prerequisite for upcoming +performance improvements. -(See the [Architectural diagram](#architectural-diagram) section at the end for -a visualisation of what this looks like) +See the [Architectural diagram](#architectural-diagram) section at the end for +a visualisation of what this looks like. ## Setting up workers A Redis server is required to manage the communication between the processes. -(The older direct TCP connections are now deprecated.) The Redis server -should be installed following the normal procedure for your distribution (e.g. -`apt install redis-server` on Debian). It is safe to use an existing Redis -deployment if you have one. +The Redis server should be installed following the normal procedure for your +distribution (e.g. `apt install redis-server` on Debian). It is safe to use an +existing Redis deployment if you have one. Once installed, check that Redis is running and accessible from the host running Synapse, for example by executing `echo PING | nc -q1 localhost 6379` and seeing @@ -65,18 +66,31 @@ https://hub.docker.com/r/matrixdotorg/synapse/. To make effective use of the workers, you will need to configure an HTTP reverse-proxy such as nginx or haproxy, which will direct incoming requests to -the correct worker, or to the main synapse instance. See [reverse_proxy.md](reverse_proxy.md) -for information on setting up a reverse proxy. +the correct worker, or to the main synapse instance. See +[reverse_proxy.md](reverse_proxy.md) for information on setting up a reverse +proxy. -To enable workers you should create a configuration file for each worker -process. Each worker configuration file inherits the configuration of the shared -homeserver configuration file. You can then override configuration specific to -that worker, e.g. the HTTP listener that it provides (if any); logging -configuration; etc. You should minimise the number of overrides though to -maintain a usable config. +When using workers, each worker process has its own configuration file which +contains settings specific to that worker, such as the HTTP listener that it +provides (if any), logging configuration, etc. + +Normally, the worker processes are configured to read from a shared +configuration file as well as the worker-specific configuration files. This +makes it easier to keep common configuration settings synchronised across all +the processes. + +The main process is somewhat special in this respect: it does not normally +need its own configuration file and can take all of its configuration from the +shared configuration file. + + +### Shared configuration + +Normally, only a couple of changes are needed to make an existing configuration +file suitable for use with workers. First, you need to enable an "HTTP replication +listener" for the main process; and secondly, you need to enable redis-based +replication. For example: -Next you need to add both a HTTP replication listener and redis config to the -shared Synapse configuration file (`homeserver.yaml`). For example: ```yaml # extend the existing `listeners` section. This defines the ports that the @@ -98,6 +112,9 @@ See the sample config for the full documentation of each option. Under **no circumstances** should the replication listener be exposed to the public internet; it has no authentication and is unencrypted. + +### Worker configuration + In the config file for each worker, you must specify the type of worker application (`worker_app`), and you should specify a unqiue name for the worker (`worker_name`). The currently available worker applications are listed below. @@ -136,6 +153,9 @@ plain HTTP endpoint on port 8083 separately serving various endpoints, e.g. Obviously you should configure your reverse-proxy to route the relevant endpoints to the worker (`localhost:8083` in the above example). + +### Running Synapse with workers + Finally, you need to start your worker processes. This can be done with either `synctl` or your distribution's preferred service manager such as `systemd`. We recommend the use of `systemd` where available: for information on setting up @@ -278,7 +298,7 @@ instance_map: host: localhost port: 8034 -streams_writers: +stream_writers: events: event_persister1 ``` @@ -398,6 +418,23 @@ all these to be folded into the `generic_worker` app and to use config to define which processes handle the various proccessing such as push notifications. +## Migration from old config + +There are two main independent changes that have been made: introducing Redis +support and merging apps into `synapse.app.generic_worker`. Both these changes +are backwards compatible and so no changes to the config are required, however +server admins are encouraged to plan to migrate to Redis as the old style direct +TCP replication config is deprecated. + +To migrate to Redis add the `redis` config as above, and optionally remove the +TCP `replication` listener from master and `worker_replication_port` from worker +config. + +To migrate apps to use `synapse.app.generic_worker` simply update the +`worker_app` option in the worker configs, and where worker are started (e.g. +in systemd service files, but not required for synctl). + + ## Architectural diagram The following shows an example setup using Redis and a reverse proxy: |