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authorerikjohnston <erikjohnston@users.noreply.github.com>2022-04-12 12:40:14 +0000
committererikjohnston <erikjohnston@users.noreply.github.com>2022-04-12 12:40:14 +0000
commit6a2b9facb00966efafa78fa942c0be36ce0d461e (patch)
tree4aa766b61824396e2cd2797dc83d6fe606f5444c /v1.57/workers.html
parentdeploy: dd5cc37aa465df8e33fd872de2528dc53740b2a6 (diff)
downloadsynapse-6a2b9facb00966efafa78fa942c0be36ce0d461e.tar.xz
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+<!DOCTYPE HTML>
+<html lang="en" class="sidebar-visible no-js light">
+    <head>
+        <!-- Book generated using mdBook -->
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+        <title>Workers - Synapse</title>
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+
+        <nav id="sidebar" class="sidebar" aria-label="Table of contents">
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+                <ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">Introduction</li><li class="chapter-item expanded "><a href="welcome_and_overview.html">Welcome and Overview</a></li><li class="chapter-item expanded affix "><li class="part-title">Setup</li><li class="chapter-item expanded "><a href="setup/installation.html">Installation</a></li><li class="chapter-item expanded "><a href="postgres.html">Using Postgres</a></li><li class="chapter-item expanded "><a href="reverse_proxy.html">Configuring a Reverse Proxy</a></li><li class="chapter-item expanded "><a href="setup/forward_proxy.html">Configuring a Forward/Outbound Proxy</a></li><li class="chapter-item expanded "><a href="turn-howto.html">Configuring a Turn Server</a></li><li class="chapter-item expanded "><a href="delegate.html">Delegation</a></li><li class="chapter-item expanded affix "><li class="part-title">Upgrading</li><li class="chapter-item expanded "><a href="upgrade.html">Upgrading 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Workers</a></li><li class="chapter-item expanded "><a href="systemd-with-workers/index.html">Systemd</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="usage/administration/index.html">Administration</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="usage/administration/admin_api/index.html">Admin API</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="admin_api/account_validity.html">Account Validity</a></li><li class="chapter-item expanded "><a href="usage/administration/admin_api/background_updates.html">Background Updates</a></li><li class="chapter-item expanded "><a href="admin_api/delete_group.html">Delete Group</a></li><li class="chapter-item expanded "><a href="admin_api/event_reports.html">Event Reports</a></li><li class="chapter-item expanded "><a href="admin_api/media_admin_api.html">Media</a></li><li class="chapter-item expanded "><a href="admin_api/purge_history_api.html">Purge History</a></li><li 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class="chapter-item expanded "><a href="replication.html">Replication</a></li><li class="chapter-item expanded "><a href="tcp_replication.html">TCP Replication</a></li></ol></li><li class="chapter-item expanded "><a href="development/internal_documentation/index.html">Internal Documentation</a></li><li><ol class="section"><li class="chapter-item expanded "><div>Single Sign-On</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="development/saml.html">SAML</a></li><li class="chapter-item expanded "><a href="development/cas.html">CAS</a></li></ol></li><li class="chapter-item expanded "><a href="development/room-dag-concepts.html">Room DAG concepts</a></li><li class="chapter-item expanded "><div>State Resolution</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="auth_chain_difference_algorithm.html">The Auth Chain Difference Algorithm</a></li></ol></li><li class="chapter-item expanded "><a href="media_repository.html">Media 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+
+                        <h1 id="scaling-synapse-via-workers"><a class="header" href="#scaling-synapse-via-workers">Scaling synapse via workers</a></h1>
+<p>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.</p>
+<p>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
+documenting it here to help admins needing a highly scalable Synapse instance
+similar to the one running <code>matrix.org</code>.</p>
+<p>All processes continue to share the same database instance, and as such,
+workers only work with PostgreSQL-based Synapse deployments. SQLite should only
+be used for demo purposes and any admin considering workers should already be
+running PostgreSQL.</p>
+<p>See also <a href="https://matrix.org/blog/2020/11/03/how-we-fixed-synapses-scalability">Matrix.org blog post</a>
+for a higher level overview.</p>
+<h2 id="main-processworker-communication"><a class="header" href="#main-processworker-communication">Main process/worker communication</a></h2>
+<p>The processes communicate with each other via a Synapse-specific protocol called
+'replication' (analogous to MySQL- or Postgres-style database replication) which
+feeds streams of newly written data between processes so they can be kept in
+sync with the database state.</p>
+<p>When configured to do so, Synapse uses a
+<a href="https://redis.io/docs/manual/pubsub/">Redis pub/sub channel</a> 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.</p>
+<p>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.</p>
+<p>If Redis support is enabled Synapse will use it as a shared cache, as well as a
+pub/sub mechanism.</p>
+<p>See the <a href="#architectural-diagram">Architectural diagram</a> section at the end for
+a visualisation of what this looks like.</p>
+<h2 id="setting-up-workers"><a class="header" href="#setting-up-workers">Setting up workers</a></h2>
+<p>A Redis server is required to manage the communication between the processes.
+The Redis server should be installed following the normal procedure for your
+distribution (e.g. <code>apt install redis-server</code> on Debian). It is safe to use an
+existing Redis deployment if you have one.</p>
+<p>Once installed, check that Redis is running and accessible from the host running
+Synapse, for example by executing <code>echo PING | nc -q1 localhost 6379</code> and seeing
+a response of <code>+PONG</code>.</p>
+<p>The appropriate dependencies must also be installed for Synapse. If using a
+virtualenv, these can be installed with:</p>
+<pre><code class="language-sh">pip install &quot;matrix-synapse[redis]&quot;
+</code></pre>
+<p>Note that these dependencies are included when synapse is installed with <code>pip install matrix-synapse[all]</code>. They are also included in the debian packages from
+<code>matrix.org</code> and in the docker images at
+https://hub.docker.com/r/matrixdotorg/synapse/.</p>
+<p>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
+<a href="reverse_proxy.html">the reverse proxy documentation</a> for information on setting up a reverse
+proxy.</p>
+<p>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.</p>
+<p>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.</p>
+<p>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.</p>
+<h3 id="shared-configuration"><a class="header" href="#shared-configuration">Shared configuration</a></h3>
+<p>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 &quot;HTTP replication
+listener&quot; for the main process; and secondly, you need to enable redis-based
+replication. Optionally, a shared secret can be used to authenticate HTTP
+traffic between workers. For example:</p>
+<pre><code class="language-yaml"># extend the existing `listeners` section. This defines the ports that the
+# main process will listen on.
+listeners:
+  # The HTTP replication port
+  - port: 9093
+    bind_address: '127.0.0.1'
+    type: http
+    resources:
+     - names: [replication]
+
+# Add a random shared secret to authenticate traffic.
+worker_replication_secret: &quot;&quot;
+
+redis:
+    enabled: true
+</code></pre>
+<p>See the sample config for the full documentation of each option.</p>
+<p>Under <strong>no circumstances</strong> should the replication listener be exposed to the
+public internet; it has no authentication and is unencrypted.</p>
+<h3 id="worker-configuration"><a class="header" href="#worker-configuration">Worker configuration</a></h3>
+<p>In the config file for each worker, you must specify the type of worker
+application (<code>worker_app</code>), and you should specify a unique name for the worker
+(<code>worker_name</code>). The currently available worker applications are listed below.
+You must also specify the HTTP replication endpoint that it should talk to on
+the main synapse process.  <code>worker_replication_host</code> should specify the host of
+the main synapse and <code>worker_replication_http_port</code> should point to the HTTP
+replication port. If the worker will handle HTTP requests then the
+<code>worker_listeners</code> option should be set with a <code>http</code> listener, in the same way
+as the <code>listeners</code> option in the shared config.</p>
+<p>For example:</p>
+<pre><code class="language-yaml">worker_app: synapse.app.generic_worker
+worker_name: worker1
+
+# The replication listener on the main synapse process.
+worker_replication_host: 127.0.0.1
+worker_replication_http_port: 9093
+
+worker_listeners:
+ - type: http
+   port: 8083
+   resources:
+     - names:
+       - client
+       - federation
+
+worker_log_config: /home/matrix/synapse/config/worker1_log_config.yaml
+</code></pre>
+<p>...is a full configuration for a generic worker instance, which will expose a
+plain HTTP endpoint on port 8083 separately serving various endpoints, e.g.
+<code>/sync</code>, which are listed below.</p>
+<p>Obviously you should configure your reverse-proxy to route the relevant
+endpoints to the worker (<code>localhost:8083</code> in the above example).</p>
+<h3 id="running-synapse-with-workers"><a class="header" href="#running-synapse-with-workers">Running Synapse with workers</a></h3>
+<p>Finally, you need to start your worker processes. This can be done with either
+<code>synctl</code> or your distribution's preferred service manager such as <code>systemd</code>. We
+recommend the use of <code>systemd</code> where available: for information on setting up
+<code>systemd</code> to start synapse workers, see
+<a href="systemd-with-workers">Systemd with Workers</a>. To use <code>synctl</code>, see
+<a href="synctl_workers.html">Using synctl with Workers</a>.</p>
+<h2 id="available-worker-applications"><a class="header" href="#available-worker-applications">Available worker applications</a></h2>
+<h3 id="synapseappgeneric_worker"><a class="header" href="#synapseappgeneric_worker"><code>synapse.app.generic_worker</code></a></h3>
+<p>This worker can handle API requests matching the following regular expressions.
+These endpoints can be routed to any worker. If a worker is set up to handle a
+stream then, for maximum efficiency, additional endpoints should be routed to that
+worker: refer to the <a href="#stream-writers">stream writers</a> section below for further
+information.</p>
+<pre><code># Sync requests
+^/_matrix/client/(r0|v3)/sync$
+^/_matrix/client/(api/v1|r0|v3)/events$
+^/_matrix/client/(api/v1|r0|v3)/initialSync$
+^/_matrix/client/(api/v1|r0|v3)/rooms/[^/]+/initialSync$
+
+# Federation requests
+^/_matrix/federation/v1/event/
+^/_matrix/federation/v1/state/
+^/_matrix/federation/v1/state_ids/
+^/_matrix/federation/v1/backfill/
+^/_matrix/federation/v1/get_missing_events/
+^/_matrix/federation/v1/publicRooms
+^/_matrix/federation/v1/query/
+^/_matrix/federation/v1/make_join/
+^/_matrix/federation/v1/make_leave/
+^/_matrix/federation/(v1|v2)/send_join/
+^/_matrix/federation/(v1|v2)/send_leave/
+^/_matrix/federation/(v1|v2)/invite/
+^/_matrix/federation/v1/event_auth/
+^/_matrix/federation/v1/exchange_third_party_invite/
+^/_matrix/federation/v1/user/devices/
+^/_matrix/federation/v1/get_groups_publicised$
+^/_matrix/key/v2/query
+^/_matrix/federation/(v1|unstable/org.matrix.msc2946)/hierarchy/
+
+# Inbound federation transaction request
+^/_matrix/federation/v1/send/
+
+# Client API requests
+^/_matrix/client/(api/v1|r0|v3|unstable)/createRoom$
+^/_matrix/client/(api/v1|r0|v3|unstable)/publicRooms$
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/joined_members$
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/context/.*$
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/members$
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/state$
+^/_matrix/client/(v1|unstable/org.matrix.msc2946)/rooms/.*/hierarchy$
+^/_matrix/client/unstable/im.nheko.summary/rooms/.*/summary$
+^/_matrix/client/(r0|v3|unstable)/account/3pid$
+^/_matrix/client/(r0|v3|unstable)/devices$
+^/_matrix/client/versions$
+^/_matrix/client/(api/v1|r0|v3|unstable)/voip/turnServer$
+^/_matrix/client/(r0|v3|unstable)/joined_groups$
+^/_matrix/client/(r0|v3|unstable)/publicised_groups$
+^/_matrix/client/(r0|v3|unstable)/publicised_groups/
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/event/
+^/_matrix/client/(api/v1|r0|v3|unstable)/joined_rooms$
+^/_matrix/client/(api/v1|r0|v3|unstable)/search$
+
+# Encryption requests
+^/_matrix/client/(r0|v3|unstable)/keys/query$
+^/_matrix/client/(r0|v3|unstable)/keys/changes$
+^/_matrix/client/(r0|v3|unstable)/keys/claim$
+^/_matrix/client/(r0|v3|unstable)/room_keys/
+
+# Registration/login requests
+^/_matrix/client/(api/v1|r0|v3|unstable)/login$
+^/_matrix/client/(r0|v3|unstable)/register$
+^/_matrix/client/v1/register/m.login.registration_token/validity$
+
+# Event sending requests
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/redact
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/send
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/state/
+^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/(join|invite|leave|ban|unban|kick)$
+^/_matrix/client/(api/v1|r0|v3|unstable)/join/
+^/_matrix/client/(api/v1|r0|v3|unstable)/profile/
+
+# Device requests
+^/_matrix/client/(r0|v3|unstable)/sendToDevice/
+
+# Account data requests
+^/_matrix/client/(r0|v3|unstable)/.*/tags
+^/_matrix/client/(r0|v3|unstable)/.*/account_data
+
+# Receipts requests
+^/_matrix/client/(r0|v3|unstable)/rooms/.*/receipt
+^/_matrix/client/(r0|v3|unstable)/rooms/.*/read_markers
+
+# Presence requests
+^/_matrix/client/(api/v1|r0|v3|unstable)/presence/
+</code></pre>
+<p>Additionally, the following REST endpoints can be handled for GET requests:</p>
+<pre><code>^/_matrix/federation/v1/groups/
+^/_matrix/client/(api/v1|r0|v3|unstable)/pushrules/
+^/_matrix/client/(r0|v3|unstable)/groups/
+</code></pre>
+<p>Pagination requests can also be handled, but all requests for a given
+room must be routed to the same instance. Additionally, care must be taken to
+ensure that the purge history admin API is not used while pagination requests
+for the room are in flight:</p>
+<pre><code>^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/messages$
+</code></pre>
+<p>Additionally, the following endpoints should be included if Synapse is configured
+to use SSO (you only need to include the ones for whichever SSO provider you're
+using):</p>
+<pre><code># for all SSO providers
+^/_matrix/client/(api/v1|r0|v3|unstable)/login/sso/redirect
+^/_synapse/client/pick_idp$
+^/_synapse/client/pick_username
+^/_synapse/client/new_user_consent$
+^/_synapse/client/sso_register$
+
+# OpenID Connect requests.
+^/_synapse/client/oidc/callback$
+
+# SAML requests.
+^/_synapse/client/saml2/authn_response$
+
+# CAS requests.
+^/_matrix/client/(api/v1|r0|v3|unstable)/login/cas/ticket$
+</code></pre>
+<p>Ensure that all SSO logins go to a single process.
+For multiple workers not handling the SSO endpoints properly, see
+<a href="https://github.com/matrix-org/synapse/issues/7530">#7530</a> and
+<a href="https://github.com/matrix-org/synapse/issues/9427">#9427</a>.</p>
+<p>Note that a HTTP listener with <code>client</code> and <code>federation</code> resources must be
+configured in the <code>worker_listeners</code> option in the worker config.</p>
+<h4 id="load-balancing"><a class="header" href="#load-balancing">Load balancing</a></h4>
+<p>It is possible to run multiple instances of this worker app, with incoming requests
+being load-balanced between them by the reverse-proxy. However, different endpoints
+have different characteristics and so admins
+may wish to run multiple groups of workers handling different endpoints so that
+load balancing can be done in different ways.</p>
+<p>For <code>/sync</code> and <code>/initialSync</code> requests it will be more efficient if all
+requests from a particular user are routed to a single instance. Extracting a
+user ID from the access token or <code>Authorization</code> header is currently left as an
+exercise for the reader. Admins may additionally wish to separate out <code>/sync</code>
+requests that have a <code>since</code> query parameter from those that don't (and
+<code>/initialSync</code>), as requests that don't are known as &quot;initial sync&quot; that happens
+when a user logs in on a new device and can be <em>very</em> resource intensive, so
+isolating these requests will stop them from interfering with other users ongoing
+syncs.</p>
+<p>Federation and client requests can be balanced via simple round robin.</p>
+<p>The inbound federation transaction request <code>^/_matrix/federation/v1/send/</code>
+should be balanced by source IP so that transactions from the same remote server
+go to the same process.</p>
+<p>Registration/login requests can be handled separately purely to help ensure that
+unexpected load doesn't affect new logins and sign ups.</p>
+<p>Finally, event sending requests can be balanced by the room ID in the URI (or
+the full URI, or even just round robin), the room ID is the path component after
+<code>/rooms/</code>. If there is a large bridge connected that is sending or may send lots
+of events, then a dedicated set of workers can be provisioned to limit the
+effects of bursts of events from that bridge on events sent by normal users.</p>
+<h4 id="stream-writers"><a class="header" href="#stream-writers">Stream writers</a></h4>
+<p>Additionally, there is <em>experimental</em> support for moving writing of specific
+streams (such as events) off of the main process to a particular worker. (This
+is only supported with Redis-based replication.)</p>
+<p>To enable this, the worker must have a HTTP replication listener configured,
+have a <code>worker_name</code> and be listed in the <code>instance_map</code> config. The same worker
+can handle multiple streams, but unless otherwise documented, each stream can only
+have a single writer.</p>
+<p>For example, to move event persistence off to a dedicated worker, the shared
+configuration would include:</p>
+<pre><code class="language-yaml">instance_map:
+    event_persister1:
+        host: localhost
+        port: 8034
+
+stream_writers:
+    events: event_persister1
+</code></pre>
+<p>Some of the streams have associated endpoints which, for maximum efficiency, should
+be routed to the workers handling that stream. See below for the currently supported
+streams and the endpoints associated with them:</p>
+<h5 id="the-events-stream"><a class="header" href="#the-events-stream">The <code>events</code> stream</a></h5>
+<p>The <code>events</code> stream experimentally supports having multiple writers, where work
+is sharded between them by room ID. Note that you <em>must</em> restart all worker
+instances when adding or removing event persisters. An example <code>stream_writers</code>
+configuration with multiple writers:</p>
+<pre><code class="language-yaml">stream_writers:
+    events:
+        - event_persister1
+        - event_persister2
+</code></pre>
+<h5 id="the-typing-stream"><a class="header" href="#the-typing-stream">The <code>typing</code> stream</a></h5>
+<p>The following endpoints should be routed directly to the worker configured as
+the stream writer for the <code>typing</code> stream:</p>
+<pre><code>^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/typing
+</code></pre>
+<h5 id="the-to_device-stream"><a class="header" href="#the-to_device-stream">The <code>to_device</code> stream</a></h5>
+<p>The following endpoints should be routed directly to the worker configured as
+the stream writer for the <code>to_device</code> stream:</p>
+<pre><code>^/_matrix/client/(r0|v3|unstable)/sendToDevice/
+</code></pre>
+<h5 id="the-account_data-stream"><a class="header" href="#the-account_data-stream">The <code>account_data</code> stream</a></h5>
+<p>The following endpoints should be routed directly to the worker configured as
+the stream writer for the <code>account_data</code> stream:</p>
+<pre><code>^/_matrix/client/(r0|v3|unstable)/.*/tags
+^/_matrix/client/(r0|v3|unstable)/.*/account_data
+</code></pre>
+<h5 id="the-receipts-stream"><a class="header" href="#the-receipts-stream">The <code>receipts</code> stream</a></h5>
+<p>The following endpoints should be routed directly to the worker configured as
+the stream writer for the <code>receipts</code> stream:</p>
+<pre><code>^/_matrix/client/(r0|v3|unstable)/rooms/.*/receipt
+^/_matrix/client/(r0|v3|unstable)/rooms/.*/read_markers
+</code></pre>
+<h5 id="the-presence-stream"><a class="header" href="#the-presence-stream">The <code>presence</code> stream</a></h5>
+<p>The following endpoints should be routed directly to the worker configured as
+the stream writer for the <code>presence</code> stream:</p>
+<pre><code>^/_matrix/client/(api/v1|r0|v3|unstable)/presence/
+</code></pre>
+<h4 id="background-tasks"><a class="header" href="#background-tasks">Background tasks</a></h4>
+<p>There is also <em>experimental</em> support for moving background tasks to a separate
+worker. Background tasks are run periodically or started via replication. Exactly
+which tasks are configured to run depends on your Synapse configuration (e.g. if
+stats is enabled).</p>
+<p>To enable this, the worker must have a <code>worker_name</code> and can be configured to run
+background tasks. For example, to move background tasks to a dedicated worker,
+the shared configuration would include:</p>
+<pre><code class="language-yaml">run_background_tasks_on: background_worker
+</code></pre>
+<p>You might also wish to investigate the <code>update_user_directory</code> and
+<code>media_instance_running_background_jobs</code> settings.</p>
+<h3 id="synapseapppusher"><a class="header" href="#synapseapppusher"><code>synapse.app.pusher</code></a></h3>
+<p>Handles sending push notifications to sygnal and email. Doesn't handle any
+REST endpoints itself, but you should set <code>start_pushers: False</code> in the
+shared configuration file to stop the main synapse sending push notifications.</p>
+<p>To run multiple instances at once the <code>pusher_instances</code> option should list all
+pusher instances by their worker name, e.g.:</p>
+<pre><code class="language-yaml">pusher_instances:
+    - pusher_worker1
+    - pusher_worker2
+</code></pre>
+<h3 id="synapseappappservice"><a class="header" href="#synapseappappservice"><code>synapse.app.appservice</code></a></h3>
+<p>Handles sending output traffic to Application Services. Doesn't handle any
+REST endpoints itself, but you should set <code>notify_appservices: False</code> in the
+shared configuration file to stop the main synapse sending appservice notifications.</p>
+<p>Note this worker cannot be load-balanced: only one instance should be active.</p>
+<h3 id="synapseappfederation_sender"><a class="header" href="#synapseappfederation_sender"><code>synapse.app.federation_sender</code></a></h3>
+<p>Handles sending federation traffic to other servers. Doesn't handle any
+REST endpoints itself, but you should set <code>send_federation: False</code> in the
+shared configuration file to stop the main synapse sending this traffic.</p>
+<p>If running multiple federation senders then you must list each
+instance in the <code>federation_sender_instances</code> option by their <code>worker_name</code>.
+All instances must be stopped and started when adding or removing instances.
+For example:</p>
+<pre><code class="language-yaml">federation_sender_instances:
+    - federation_sender1
+    - federation_sender2
+</code></pre>
+<h3 id="synapseappmedia_repository"><a class="header" href="#synapseappmedia_repository"><code>synapse.app.media_repository</code></a></h3>
+<p>Handles the media repository. It can handle all endpoints starting with:</p>
+<pre><code>/_matrix/media/
+</code></pre>
+<p>... and the following regular expressions matching media-specific administration APIs:</p>
+<pre><code>^/_synapse/admin/v1/purge_media_cache$
+^/_synapse/admin/v1/room/.*/media.*$
+^/_synapse/admin/v1/user/.*/media.*$
+^/_synapse/admin/v1/media/.*$
+^/_synapse/admin/v1/quarantine_media/.*$
+^/_synapse/admin/v1/users/.*/media$
+</code></pre>
+<p>You should also set <code>enable_media_repo: False</code> in the shared configuration
+file to stop the main synapse running background jobs related to managing the
+media repository. Note that doing so will prevent the main process from being
+able to handle the above endpoints.</p>
+<p>In the <code>media_repository</code> worker configuration file, configure the http listener to
+expose the <code>media</code> resource. For example:</p>
+<pre><code class="language-yaml">worker_listeners:
+ - type: http
+   port: 8085
+   resources:
+     - names:
+       - media
+</code></pre>
+<p>Note that if running multiple media repositories they must be on the same server
+and you must configure a single instance to run the background tasks, e.g.:</p>
+<pre><code class="language-yaml">media_instance_running_background_jobs: &quot;media-repository-1&quot;
+</code></pre>
+<p>Note that if a reverse proxy is used , then <code>/_matrix/media/</code> must be routed for both inbound client and federation requests (if they are handled separately).</p>
+<h3 id="synapseappuser_dir"><a class="header" href="#synapseappuser_dir"><code>synapse.app.user_dir</code></a></h3>
+<p>Handles searches in the user directory. It can handle REST endpoints matching
+the following regular expressions:</p>
+<pre><code>^/_matrix/client/(r0|v3|unstable)/user_directory/search$
+</code></pre>
+<p>When using this worker you must also set <code>update_user_directory: false</code> in the
+shared configuration file to stop the main synapse running background
+jobs related to updating the user directory.</p>
+<p>Above endpoint is not <em>required</em> to be routed to this worker. By default,
+<code>update_user_directory</code> is set to <code>true</code>, which means the main process
+will handle updates. All workers configured with <code>client</code> can handle the above
+endpoint as long as either this worker or the main process are configured to
+handle it, and are online.</p>
+<p>If <code>update_user_directory</code> is set to <code>false</code>, and this worker is not running,
+the above endpoint may give outdated results.</p>
+<h3 id="synapseappfrontend_proxy"><a class="header" href="#synapseappfrontend_proxy"><code>synapse.app.frontend_proxy</code></a></h3>
+<p>Proxies some frequently-requested client endpoints to add caching and remove
+load from the main synapse. It can handle REST endpoints matching the following
+regular expressions:</p>
+<pre><code>^/_matrix/client/(r0|v3|unstable)/keys/upload
+</code></pre>
+<p>If <code>use_presence</code> is False in the homeserver config, it can also handle REST
+endpoints matching the following regular expressions:</p>
+<pre><code>^/_matrix/client/(api/v1|r0|v3|unstable)/presence/[^/]+/status
+</code></pre>
+<p>This &quot;stub&quot; presence handler will pass through <code>GET</code> request but make the
+<code>PUT</code> effectively a no-op.</p>
+<p>It will proxy any requests it cannot handle to the main synapse instance. It
+must therefore be configured with the location of the main instance, via
+the <code>worker_main_http_uri</code> setting in the <code>frontend_proxy</code> worker configuration
+file. For example:</p>
+<pre><code class="language-yaml">worker_main_http_uri: http://127.0.0.1:8008
+</code></pre>
+<h3 id="historical-apps"><a class="header" href="#historical-apps">Historical apps</a></h3>
+<p><em>Note:</em> Historically there used to be more apps, however they have been
+amalgamated into a single <code>synapse.app.generic_worker</code> app. The remaining apps
+are ones that do specific processing unrelated to requests, e.g. the <code>pusher</code>
+that handles sending out push notifications for new events. The intention is for
+all these to be folded into the <code>generic_worker</code> app and to use config to define
+which processes handle the various proccessing such as push notifications.</p>
+<h2 id="migration-from-old-config"><a class="header" href="#migration-from-old-config">Migration from old config</a></h2>
+<p>There are two main independent changes that have been made: introducing Redis
+support and merging apps into <code>synapse.app.generic_worker</code>. 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.</p>
+<p>To migrate to Redis add the <code>redis</code> config as above, and optionally remove the
+TCP <code>replication</code> listener from master and <code>worker_replication_port</code> from worker
+config.</p>
+<p>To migrate apps to use <code>synapse.app.generic_worker</code> simply update the
+<code>worker_app</code> option in the worker configs, and where worker are started (e.g.
+in systemd service files, but not required for synctl).</p>
+<h2 id="architectural-diagram"><a class="header" href="#architectural-diagram">Architectural diagram</a></h2>
+<p>The following shows an example setup using Redis and a reverse proxy:</p>
+<pre><code>                     Clients &amp; Federation
+                              |
+                              v
+                        +-----------+
+                        |           |
+                        |  Reverse  |
+                        |  Proxy    |
+                        |           |
+                        +-----------+
+                            | | |
+                            | | | HTTP requests
+        +-------------------+ | +-----------+
+        |                 +---+             |
+        |                 |                 |
+        v                 v                 v
++--------------+  +--------------+  +--------------+  +--------------+
+|   Main       |  |   Generic    |  |   Generic    |  |  Event       |
+|   Process    |  |   Worker 1   |  |   Worker 2   |  |  Persister   |
++--------------+  +--------------+  +--------------+  +--------------+
+      ^    ^          |   ^   |         |   ^   |          ^    ^
+      |    |          |   |   |         |   |   |          |    |
+      |    |          |   |   |  HTTP   |   |   |          |    |
+      |    +----------+&lt;--|---|---------+   |   |          |    |
+      |                   |   +-------------|--&gt;+----------+    |
+      |                   |                 |                   |
+      |                   |                 |                   |
+      v                   v                 v                   v
+====================================================================
+                                                         Redis pub/sub channel
+</code></pre>
+
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