Add systemd setup that supports workers (#4662)

This setup is a way to manage workers with systemd. It does however not
require workers. You can use this setup without workers. You just have
to make sure that the homeserver is forking and writes its PID file
to the location the service is looking in.

The currently distributed setup in the debian package does not work in
conjunction with workers.

* Adds changelog

* Lets systemd handle the forking

Sets all services to `type=simple` and disables daemonizing on the
synapse side.

* Formats readme to 80 columns per line

* Allows for full restart of all workers

* Changes README to reflect the new setup

* Adds dot to end of changelog file

* Removes surplus word

Co-Authored-By: targodan <targodan@users.noreply.github.com>

* Adds missing word

Co-Authored-By: targodan <targodan@users.noreply.github.com>

* Fixes linebreak

Co-Authored-By: targodan <targodan@users.noreply.github.com>

* Fixes unit type

changelog.d/4662.misc

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+Add a systemd setup that supports synapse workers. Contributed by Luca Corbatto.

contrib/systemd-with-workers/README.md

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+# Setup Synapse with Workers and Systemd
+
+This is a setup for managing synapse with systemd including support for
+managing workers. It provides a `matrix-synapse`, as well as a
+`matrix-synapse-worker@` service for any workers you require. Additionally to
+group the required services it sets up a `matrix.target`. You can use this to
+automatically start any bot- or bridge-services. More on this in
+[Bots and Bridges](#bots-and-bridges).
+
+See the folder [system](system) for any service and target files.
+
+The folder [workers](workers) contains an example configuration for the
+`federation_reader` worker. Pay special attention to the name of the
+configuration file. In order to work with the `matrix-synapse-worker@.service`
+service, it needs to have the exact same name as the worker app.
+
+This setup expects neither the homeserver nor any workers to fork. Forking is
+handled by systemd.
+
+## Setup
+
+1. Adjust your matrix configs. Make sure that the worker config files have the
+exact same name as the worker app. Compare `matrix-synapse-worker@.service` for
+why. You can find an example worker config in the [workers](workers) folder. See
+below for relevant settings in the `homeserver.yaml`.
+2. Copy the `*.service` and `*.target` files in [system](system) to
+`/etc/systemd/system`.
+3. `systemctl enable matrix-synapse.service` this adds the homeserver
+app to the `matrix.target`
+4. *Optional.* `systemctl enable
+matrix-synapse-worker@federation_reader.service` this adds the federation_reader
+app to the `matrix-synapse.service`
+5. *Optional.* Repeat step 4 for any additional workers you require.
+6. *Optional.* Add any bots or bridges by enabling them.
+7. Start all matrix related services via `systemctl start matrix.target`
+8. *Optional.* Enable autostart of all matrix related services on system boot
+via `systemctl enable matrix.target`
+
+## Usage
+
+After you have setup you can use the following commands to manage your synapse
+installation:
+
+```
+# Start matrix-synapse, all workers and any enabled bots or bridges.
+systemctl start matrix.target
+
+# Restart matrix-synapse and all workers (not necessarily restarting bots
+# or bridges, see "Bots and Bridges")
+systemctl restart matrix-synapse.service
+
+# Stop matrix-synapse and all workers (not necessarily restarting bots
+# or bridges, see "Bots and Bridges")
+systemctl stop matrix-synapse.service
+
+# Restart a specific worker (i. e. federation_reader), the homeserver is
+# unaffected by this.
+systemctl restart matrix-synapse-worker@federation_reader.service
+
+# Add a new worker (assuming all configs are setup already)
+systemctl enable matrix-synapse-worker@federation_writer.service
+systemctl restart matrix-synapse.service
+```
+
+## The Configs
+
+Make sure the `worker_app` is set in the `homeserver.yaml` and it does not fork.
+
+```
+worker_app: synapse.app.homeserver 
+daemonize: false
+```
+
+None of the workers should fork, as forking is handled by systemd. Hence make
+sure this is present in all worker config files.
+
+```
+worker_daemonize: false
+```
+
+The config files of all workers are expected to be located in
+`/etc/matrix-synapse/workers`. If you want to use a different location you have
+to edit the provided `*.service` files accordingly.  
+
+## Bots and Bridges
+
+Most bots and bridges do not care if the homeserver goes down or is restarted.
+Depending on the implementation this may crash them though. So look up the docs
+or ask the community of the specific bridge or bot you want to run to make sure
+you choose the correct setup.
+
+Whichever configuration you choose, after the setup the following will enable
+automatically starting (and potentially restarting) your bot/bridge with the
+`matrix.target`.
+
+```
+systemctl enable <yourBotOrBridgeName>.service
+```
+
+**Note** that from an inactive synapse the bots/bridges will only be started with
+synapse if you start the `matrix.target`, not if you start the
+`matrix-synapse.service`. This is on purpose. Think of `matrix-synapse.service`
+as *just* synapse, but `matrix.target` being anything matrix related, including
+synapse and any and all enabled bots and bridges.
+
+### Start with synapse but ignore synapse going down
+
+If the bridge can handle shutdowns of the homeserver you'll want to install the
+service in the `matrix.target` and optionally add a
+`After=matrix-synapse.service` dependency to have the bot/bridge start after
+synapse on starting everything.
+
+In this case the service file should look like this.
+
+```
+[Unit]
+# ...
+# Optional, this will only ensure that if you start everything, synapse will
+# be started before the bot/bridge will be started.
+After=matrix-synapse.service
+
+[Service]
+# ...
+
+[Install]
+WantedBy=matrix.target
+```
+
+### Stop/restart when synapse stops/restarts
+
+If the bridge can't handle shutdowns of the homeserver you'll still want to
+install the service in the `matrix.target` but also have to specify the
+`After=matrix-synapse.service` *and* `BindsTo=matrix-synapse.service`
+dependencies to have the bot/bridge stop/restart with synapse.
+
+In this case the service file should look like this.
+
+```
+[Unit]
+# ...
+# Mandatory
+After=matrix-synapse.service
+BindsTo=matrix-synapse.service
+
+[Service]
+# ...
+
+[Install]
+WantedBy=matrix.target
+```

contrib/systemd-with-workers/system/matrix-synapse-worker@.service

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+[Unit]
+Description=Synapse Matrix Worker
+After=matrix-synapse.service
+BindsTo=matrix-synapse.service
+
+[Service]
+Type=simple
+User=matrix-synapse
+WorkingDirectory=/var/lib/matrix-synapse
+EnvironmentFile=/etc/default/matrix-synapse
+ExecStart=/opt/venvs/matrix-synapse/bin/python -m synapse.app.%i --config-path=/etc/matrix-synapse/homeserver.yaml --config-path=/etc/matrix-synapse/conf.d/ --config-path=/etc/matrix-synapse/workers/%i.yaml
+ExecReload=/bin/kill -HUP $MAINPID
+Restart=always
+RestartSec=3
+
+[Install]
+WantedBy=matrix-synapse.service

contrib/systemd-with-workers/system/matrix-synapse.service

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+[Unit]
+Description=Synapse Matrix Homeserver
+
+[Service]
+Type=simple
+User=matrix-synapse
+WorkingDirectory=/var/lib/matrix-synapse
+EnvironmentFile=/etc/default/matrix-synapse
+ExecStartPre=/opt/venvs/matrix-synapse/bin/python -m synapse.app.homeserver --config-path=/etc/matrix-synapse/homeserver.yaml --config-path=/etc/matrix-synapse/conf.d/ --generate-keys
+ExecStart=/opt/venvs/matrix-synapse/bin/python -m synapse.app.homeserver --config-path=/etc/matrix-synapse/homeserver.yaml --config-path=/etc/matrix-synapse/conf.d/
+ExecReload=/bin/kill -HUP $MAINPID
+Restart=always
+RestartSec=3
+
+[Install]
+WantedBy=matrix.target

contrib/systemd-with-workers/system/matrix.target

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+[Unit]
+Description=Contains matrix services like synapse, bridges and bots
+After=network.target
+AllowIsolate=no
+
+[Install]
+WantedBy=multi-user.target

contrib/systemd-with-workers/workers/federation_reader.yaml

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+worker_app: synapse.app.federation_reader
+
+worker_replication_host: 127.0.0.1
+worker_replication_port: 9092
+worker_replication_http_port: 9093
+
+worker_listeners:
+    - type: http
+      port: 8011
+      resources:
+          - names: [federation]
+
+worker_daemonize: false
+worker_log_config: /etc/matrix-synapse/federation-reader-log.yaml