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:
**NOTE**: Disabling `matrix-nginx-proxy` (`matrix_nginx_proxy_enabled: false`) (that is, [using your own other webserver](configuring-playbook-own-webserver.md) when running a Synapse worker setup is likely to cause various troubles (see [this issue](https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2090)).
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 ;