First bit of documentation for workers.

matrix/synapse/monolithic/README.md

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-
-# Standard, monolithic configuration
-
-This configuration will be enough for most installations.
-
-

matrix/synapse/workers.md

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+---
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+---
+
+# Worker-based setup
+
+Very busy servers are brought down because a single thread can't keep up with
+the load. So you want to create several threads for different types of work.
+
+See this [Matrix blog](https://matrix.org/blog/2020/11/03/how-we-fixed-synapse-s-scalability/)
+for some background information.
+
+
+# Redis
+
+First step is to install Redis.
+
+```
+apt install redis-server
+```
+
+For less overhead we use a UNIX socket instead of a network connection to
+localhost. Disable the TCP listener and enable the socket in
+`/etc/redis/redis.conf`:
+
+```
+port 0
+
+unixsocket /run/redis/redis-server.sock
+unixsocketperm 770
+```
+
+Our matrix user (`matrix-synapse`) has to be able to read from and write to
+that socket, which is created by Redis and owned by `redis:redis`, so we add
+user `matrix-synapse` to the group `redis`.
+
+```
+adduser matrix-synapse redis
+```
+
+Restart Redis for these changes to take effect. Check if port 6379 is no
+longer active, and if the socketfile `/run/redis/redis-server.sock` exists.
+
+
+# Synapse
+
+First, create the directory where all the socket files for workers will come,
+and give it the correct user, group and permission:
+
+```
+mkdir /run/matrix-synapse
+dpkg-statoverride --add --update matrix-synapse matrix-synapse 0770 /run/matrix-synapse
+```
+
+Add a replication listener:
+
+```
+listeners:
+
+  ...
+
+  - path: /run/matrix-synapse/replication.sock
+    mode: 0660
+    type: http
+    resources:
+      - names:
+        - replication 
+```
+
+Check if the socket is created and has the correct permissions. Now point
+Synapse at Redis in `conf.d/redis.yaml`:
+
+```
+redis:
+  enabled: true
+  path: /run/redis/redis-server.sock
+```
+
+Check if Synapse can connect to Redis via the socket, you should find log
+entries like this:
+
+```
+synapse.replication.tcp.redis - 292 - INFO - sentinel - Connecting to redis server UNIXAddress('/run/redis/redis-server.sock')
+synapse.util.httpresourcetree - 56 - INFO - sentinel - Attaching <synapse.replication.http.ReplicationRestResource object at 0x7f95f850d15
+0> to path b'/_synapse/replication'
+synapse.replication.tcp.redis - 126 - INFO - sentinel - Connected to redis
+synapse.replication.tcp.redis - 138 - INFO - subscribe-replication-0 - Sending redis SUBSCRIBE for ['matrix.example.com/USER_IP', 'matrix.example.com']
+synapse.replication.tcp.redis - 141 - INFO - subscribe-replication-0 - Successfully subscribed to redis stream, sending REPLICATE command
+synapse.replication.tcp.redis - 146 - INFO - subscribe-replication-0 - REPLICATE successfully sent
+```
+
+

matrix/synapse/workers/README.md

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-# Advanced configuration with workers
-
-This configuration allows optimizing performance, meant for big, busy
-installations.
-
-