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docs/configuring-playbook-synapse.md

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+# Configuring Synapse (optional)
+
+By default, this playbook configures the [Synapse](https://github.com/matrix-org/synapse) Matrix server, so that it works for the general case.
+If that's enough for you, you can skip this document.
+
+The playbook provides lots of customization variables you could use to change Synapse's settings.
+
+Their defaults are defined in [`roles/matrix-synapse/defaults/main.yml`](../roles/matrix-synapse/defaults/main.yml) and they ultimately end up in the generated `/matrix/synapse/config/homeserver.yaml` file (on the server). This file is generated from the [`roles/matrix-synapse/templates/synapse/homeserver.yaml.j2`](../roles/matrix-synapse/templates/synapse/homeserver.yaml.j2) template.
+
+**If there's an existing variable** which controls a setting you wish to change, you can simply define that variable in your configuration file (`inventory/host_vars/matrix.<your-domain>/vars.yml`) and [re-run the playbook](installing.md) to apply the changes.
+
+Alternatively, **if there is no pre-defined variable** for a Synapse setting you wish to change:
+
+- you can either **request a variable to be created** (or you can submit such a contribution yourself). Keep in mind that it's **probably not a good idea** to create variables for each one of Synapse's various settings that rarely get used.
+
+- or, you can **extend and override the default configuration** ([`homeserver.yaml.j2`](../roles/matrix-synapse/templates/synapse/homeserver.yaml.j2)) by making use of the `matrix_synapse_configuration_extension_yaml` variable. You can find information about this in [`roles/matrix-synapse/defaults/main.yml`](../roles/matrix-synapse/defaults/main.yml).
+
+- or, if extending the configuration is still not powerful enough for your needs, you can **override the configuration completely** using `matrix_synapse_configuration` (or `matrix_synapse_configuration_yaml`). You can find information about this in [`roles/matrix-synapse/defaults/main.yml`](../roles/matrix-synapse/defaults/main.yml).
+
+
+## Load balancing with workers
+
+To have Synapse gracefully handle thousands of users, worker support should be enabled. It factors out some homeserver tasks and spreads the load of incoming client and server-to-server traffic between multiple processes. More information can be found in the [official Synapse workers documentation](https://github.com/matrix-org/synapse/blob/master/docs/workers.md).
+
+To enable Synapse worker support, update your `inventory/host_vars/matrix.DOMAIN/vars.yml` file:
+
+```yaml
+matrix_synapse_workers_enabled: true
+```
+
+We support a few configuration presets (`matrix_synapse_workers_preset: one-of-each` being the default configuration):
+- `little-federation-helper` - a very minimal worker configuration to improve federation performance
+- `one-of-each` - one worker of each supported type
+
+If you'd like more customization power, you can start with one of the presets and tweak various `matrix_synapse_workers_*_count` variables manually.
+
+If you increase worker counts too much, you may need to increase the maximum number of Postgres connections too (example):
+
+```yaml
+matrix_postgres_process_extra_arguments: [
+  "-c 'max_connections=200'"
+]
+```
+
+If you're using the default setup (the `matrix-nginx-proxy` webserver being enabled) or you're using your own `nginx` server (which imports the configuration files generated by the playbook), you're good to go. If you use some other webserver, you may need to tweak your reverse-proxy setup manually to forward traffic to the various workers.
+
+In case any problems occur, make sure to have a look at the [list of synapse issues about workers](https://github.com/matrix-org/synapse/issues?q=workers+in%3Atitle) and your `journalctl --unit 'matrix-*'`.
+
+
+## Synapse Admin
+
+Certain Synapse administration tasks (managing users and rooms, etc.) can be performed via a web user-interace, if you install [Synapse Admin](configuring-playbook-synapse-admin.md).
+
+
+## Synapse + OpenID Connect for Single-Sign-On
+
+If you'd like to use OpenID Connect authentication with Synapse, you'll need some additional reverse-proxy configuration (see [our nginx reverse-proxy doc page](configuring-playbook-nginx.md#synapse-openid-connect-for-single-sign-on)).
+
+In case you encounter errors regarding the parsing of the variables, you can try to add `{% raw %}` and `{% endraw %}` blocks around them. For example ;
+
+```
+ - idp_id: keycloak
+        idp_name: "Keycloak"
+        issuer: "https://url.ix/auth/realms/x"
+        client_id: "matrix"
+        client_secret: "{{ vault_synapse_keycloak }}"
+        scopes: ["openid", "profile"]
+        authorization_endpoint: "https://url.ix/auth/realms/x/protocol/openid-connect/auth"
+        token_endpoint: "https://url.ix/auth/realms/x/protocol/openid-connect/token"
+        userinfo_endpoint: "https://url.ix/auth/realms/x/protocol/openid-connect/userinfo"
+        user_mapping_provider:
+          config:
+            display_name_template: "{% raw %}{{ user.given_name }}{% endraw %} {% raw %}{{ user.family_name }}{% endraw %}"
+            email_template: "{% raw %}{{ user.email }}{% endraw %}"
+```
+