Their defaults are defined in [`roles/custom/matrix-synapse/defaults/main.yml`](../roles/custom/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/custom/matrix-synapse/templates/synapse/homeserver.yaml.j2`](../roles/custom/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/custom/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/custom/matrix-synapse/defaults/main.yml`](../roles/custom/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/custom/matrix-synapse/defaults/main.yml`](../roles/custom/matrix-synapse/defaults/main.yml).
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:
When Synapse workers are enabled, the integrated [Postgres database is tuned](maintenance-postgres.md#tuning-postgresql), so that the maximum number of Postgres connections are increased from `200` to `500`. If you need to decrease or increase the number of maximum Postgres connections further, use the `devture_postgres_max_connections` variable.
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-*'`.
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).
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)).
This example configuration is for [keycloak](https://www.keycloak.org/), an opensource Identity Provider maintained by Red Hat.
For more detailed documentation on available options and how to setup keycloak, see the [Synapse documentation on OpenID Connect with keycloak](https://github.com/matrix-org/synapse/blob/develop/docs/openid.md#keycloak).
In case you encounter errors regarding the parsing of the variables, you can try to add `{% raw %}` and `{% endraw %}` blocks around them. For example ;
[Templates](https://github.com/matrix-org/synapse/blob/develop/docs/templates.md) are used by Synapse for showing **certain web pages** handled by the server, as well as for **email notifications**.
This playbook allows you to customize the default templates (see the [`synapse/res/templates` directory](https://github.com/matrix-org/synapse/tree/develop/synapse/res/templates)).
If template customization is enabled, the playbook will build a custom container image based on the official one.
Your custom templates need to live in a public or private git repository. This repository will be cloned during Synapse image customization (during the playbook run).
To enable template customizations, use a configuration (`inventory/host_vars/matrix.DOMAIN/vars.yml`) like this:
```yaml
# If you'd like to ensure that the customized image is built each time the playbook runs, enable this.
# Otherwise, the customized image will only be rebuilt whenever the Synapse version changes (once every ~2 weeks).
As mentioned in Synapse's Templates documentation, Synapse will fall back to its own templates if a template is not found in that directory.
Due to this, it's recommended to only store and maintain template files in your repository if you need to make custom changes. Other files (which you don't need to change), should not be duplicated, so that you don't need to worry about getting out-of-sync with the original Synapse templates.