From 85155654c52bb9999b6b4bcbcf84cd68505d4c82 Mon Sep 17 00:00:00 2001 From: Neil Johnson Date: Mon, 11 May 2020 13:21:15 +0100 Subject: [PATCH] Documentation on setting up redis (#7446) --- changelog.d/7446.feature | 1 + docs/workers.md | 165 +++++++++++++++++++++++++-------------- 2 files changed, 107 insertions(+), 59 deletions(-) create mode 100644 changelog.d/7446.feature diff --git a/changelog.d/7446.feature b/changelog.d/7446.feature new file mode 100644 index 000000000..ce6140fdd --- /dev/null +++ b/changelog.d/7446.feature @@ -0,0 +1 @@ +Add support for running replication over Redis when using workers. diff --git a/docs/workers.md b/docs/workers.md index cc0b23197..7512eff43 100644 --- a/docs/workers.md +++ b/docs/workers.md @@ -1,23 +1,31 @@ # 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