Decrease default Synapse logging level

Also discussed previously in #213 (Github Pull Request).

shared-secret-auth and rest-auth logging is still at `INFO`
intentionally, as user login events seem more important to keep.
Those modules typically don't spam as much.

CHANGELOG.md

@@ -1,3 +1,18 @@
+# 2019-08-03
+
+## Synapse logging level has been reduced to WARNING
+
+After [some discussion in our support room](https://matrix.to/#/!PukFFdIcHgtaaHZflT:devture.com/$156476852524179TBeKy:matrix.org?via=devture.com&via=matrix.org&via=librem.one), we've decided to change the default logging level for Synapse from `INFO` to `WARNING`.
+
+This greatly reduces the number of log messages that are being logged, leading to:
+
+- much less disk space dedicated to Synapse and thus, logs kept for longer
+- easier to find some important `WARNING`, `ERROR` and `CRITICAL` messages, as they're not longer buried in thousands of non-important `INFO` messages
+
+If you'd like to track down an issue, you [can always increase the logging level as described here](./docs/maintenance-and-troubleshooting.md#increasing-synapse-logging).
+
+
+
 # 2019-07-08
 
 ## Synapse Maintenance docs and synapse-janitor support are available

docs/maintenance-and-troubleshooting.md

@@ -16,6 +16,24 @@ You can see the logs by using journalctl. Example:
 sudo journalctl -fu matrix-synapse
 ```
 
+
+## Increasing Synapse logging
+
+Because the [Synapse](https://github.com/matrix-org/synapse) Matrix server is originally very chatty when it comes to logging, we intentionally reduce its [logging level](https://docs.python.org/3/library/logging.html#logging-levels) from `INFO` to `WARNING`.
+
+If you'd like to debug an issue or [report a Synapse bug](https://github.com/matrix-org/synapse/issues/new/choose) to the developers, it'd be better if you temporarily increasing the logging level to `INFO` or even `DEBUG`.
+
+Example configuration (`inventory/host_vars/matrix.DOMAIN/vars.yml`):
+
+```yaml
+matrix_synapse_log_level: "DEBUG"
+matrix_synapse_storage_sql_log_level: "DEBUG"
+matrix_synapse_root_log_level: "DEBUG"
+```
+
+Re-run the playbook after making these configuration changes.
+
+
 ## Postgres
 
 See the dedicated [PostgreSQL Maintenance](maintenance-postgres.md) documentation page.

roles/matrix-synapse/defaults/main.yml

@@ -77,9 +77,9 @@ matrix_synapse_tmp_directory_size_mb: "{{ matrix_synapse_max_upload_size_mb * 50
 # Possible options are defined here https://docs.python.org/3/library/logging.html#logging-levels
 # warning: setting log level to DEBUG will make synapse log sensitive information such
 # as access tokens
-matrix_synapse_log_level: "INFO"
-matrix_synapse_storage_sql_log_level: "INFO"
-matrix_synapse_root_log_level: "INFO"
+matrix_synapse_log_level: "WARNING"
+matrix_synapse_storage_sql_log_level: "WARNING"
+matrix_synapse_root_log_level: "WARNING"
 
 # Rate limits
 matrix_synapse_rc_message: