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Documentation on setting up redis (#7446)

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Add support for running replication over Redis when using workers.

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docs/workers.md
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# Scaling synapse via workers
Synapse has experimental support for splitting out functionality into
multiple separate python processes, helping greatly with scalability. These
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.
All of the below is highly experimental and subject to change as Synapse evolves,
but documenting it here to help folks needing highly scalable Synapses similar
to the one running matrix.org!
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 `matrix.org`.
All processes continue to share the same database instance, and as such, workers
only work with postgres based synapse deployments (sharing a single sqlite
across multiple processes is a recipe for disaster, plus you should be using
postgres anyway if you care about scalability).
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.
The workers communicate with the master synapse process via a synapse-specific
TCP protocol called 'replication' - analogous to MySQL or Postgres style
database replication; feeding a stream of relevant data to the workers so they
can be kept in sync with the main synapse process and database state.
## Master/worker communication
The workers communicate with the master process via a Synapse-specific protocol
called 'replication' (analogous to MySQL- or Postgres-style database
replication) which feeds a stream of relevant data from the master to the
workers so they can be kept in sync with the master process and database state.
Additionally, workers may make HTTP requests to the master, to send information
in the other direction. Typically this is used for operations which need to
wait for a reply - such as sending an event.
## Configuration
@ -27,66 +35,61 @@ the correct worker, or to the main synapse instance. Note that this includes
requests made to the federation port. See [reverse_proxy.md](reverse_proxy.md)
for information on setting up a reverse proxy.
To enable workers, you need to add two replication listeners to the master
synapse, e.g.:
To enable workers, you need to add *two* replication listeners to the
main Synapse configuration file (`homeserver.yaml`). For example:
listeners:
# The TCP replication port
- port: 9092
bind_address: '127.0.0.1'
type: replication
# The HTTP replication port
- port: 9093
bind_address: '127.0.0.1'
type: http
resources:
- names: [replication]
```yaml
listeners:
# The TCP replication port
- port: 9092
bind_address: '127.0.0.1'
type: replication
# The HTTP replication port
- port: 9093
bind_address: '127.0.0.1'
type: http
resources:
- names: [replication]
```
Under **no circumstances** should these replication API listeners be exposed to
the public internet; it currently implements no authentication whatsoever and is
unencrypted.
the public internet; they have no authentication and are unencrypted.
(Roughly, the TCP port is used for streaming data from the master to the
workers, and the HTTP port for the workers to send data to the main
synapse process.)
You then create a set of configs for the various worker processes. These
should be worker configuration files, and should be stored in a dedicated
subdirectory, to allow synctl to manipulate them.
Each worker configuration file inherits the configuration of the main 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.
You should then create a set of configs for the various worker processes. Each
worker configuration file inherits the configuration of the main 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.
In the config file for each worker, you must specify the type of worker
application (`worker_app`). The currently available worker applications are
listed below. You must also specify the replication endpoints that it's talking
to on the main synapse process. `worker_replication_host` should specify the
host of the main synapse, `worker_replication_port` should point to the TCP
listed below. You must also specify the replication endpoints that it should
talk to on the main synapse process. `worker_replication_host` should specify
the host of the main synapse, `worker_replication_port` should point to the TCP
replication listener port and `worker_replication_http_port` should point to
the HTTP replication port.
Currently, the `event_creator` and `federation_reader` workers require specifying
`worker_replication_http_port`.
For example:
For instance:
```yaml
worker_app: synapse.app.synchrotron
worker_app: synapse.app.synchrotron
# The replication listener on the synapse to talk to.
worker_replication_host: 127.0.0.1
worker_replication_port: 9092
worker_replication_http_port: 9093
# The replication listener on the synapse to talk to.
worker_replication_host: 127.0.0.1
worker_replication_port: 9092
worker_replication_http_port: 9093
worker_listeners:
- type: http
port: 8083
resources:
- names:
- client
worker_listeners:
- type: http
port: 8083
resources:
- names:
- client
worker_log_config: /home/matrix/synapse/config/synchrotron_log_config.yaml
worker_log_config: /home/matrix/synapse/config/synchrotron_log_config.yaml
```
...is a full configuration for a synchrotron worker instance, which will expose a
plain HTTP `/sync` endpoint on port 8083 separately from the `/sync` endpoint provided
@ -101,6 +104,50 @@ recommend the use of `systemd` where available: for information on setting up
`systemd` to start synapse workers, see
[systemd-with-workers](systemd-with-workers). To use `synctl`, see below.
### **Experimental** support for replication over redis
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). This is an
alternative to direct TCP connections to the master: rather than all the
workers connecting to the master, all the workers and the master connect to
Redis, which relays replication commands between processes. This can give a
significant cpu saving on the master and will be a prerequisite for upcoming
performance improvements.
Note that this support is currently experimental; you may experience lost
messages and similar problems! It is strongly recommended that admins setting
up workers for the first time use direct TCP replication as above.
To configure Synapse to use Redis:
1. Install Redis following the normal procedure for your distribution - for
example, on Debian, `apt install redis-server`. (It is safe to use an
existing Redis deployment if you have one: we use a pub/sub stream named
according to the `server_name` of your synapse server.)
2. Check Redis is running and accessible: you should be able to `echo PING | nc -q1
localhost 6379` and get a response of `+PONG`.
3. Install the python prerequisites. If you installed synapse into a
virtualenv, this can be done with:
```sh
pip install matrix-synapse[redis]
```
The debian packages from matrix.org already include the required
dependencies.
4. Add config to the shared configuration (`homeserver.yaml`):
```yaml
redis:
enabled: true
```
Optional parameters which can go alongside `enabled` are `host`, `port`,
`password`. Normally none of these are required.
5. Restart master and all workers.
Once redis replication is in use, `worker_replication_port` is redundant and
can be removed from the worker configuration files. Similarly, the
configuration for the `listener` for the TCP replication port can be removed
from the main configuration file. Note that the HTTP replication port is
still required.
### Using synctl
If you want to use `synctl` to manage your synapse processes, you will need to