Monitoring: Could not find plugin definition for data source

If the Plesk “Monitoring” extension does not display any content, the Grafana service must be configured.

The Grafana logs indicate that the plesk-json-backend-datasource plugin cannot be loaded due to a missing signature:

logger=plugin.loader t=2022-10-13T18:34:22.032073521+02:00 level=warn msg="Skipping loading plugin due to problem with signature" pluginID=plesk-json-backend-datasource status=unsigned
logger=context userId=1 orgId=1 uname=admin t=2022-10-13T18:38:47.239550914+02:00 level=error msg="Could not find plugin definition for data source" datasource_type=plesk-json-backend-datasource
logger=context userId=1 orgId=1 uname=admin t=2022-10-13T18:38:47.327509741+02:00 level=error msg="Could not find plugin definition for data source" datasource_type=plesk-json-backend-datasource
logger=context userId=1 orgId=1 uname=admin t=2022-10-13T18:38:47.327538896+02:00 level=error msg="Could not find plugin definition for data source" datasource_type=plesk-json-backend-datasource
logger=context userId=1 orgId=1 uname=admin t=2022-10-13T18:38:47.334118317+02:00 level=error msg="Could not find plugin definition for data source" datasource_type=plesk-json-backend-datasource

The Grafana configuration file at /etc/grafana/grafana.ini only allows a comma-separated list of plugins. There is an unwanted space between two or more plugins in the configuration:

Open the grafana.ini file and search for the following text:

allow_loading_unsigned_plugins = grafana-simple-json-backend-datasource, plesk-json-backend-datasource

Remove the spaces between all plugins so that the plugins are separated only by a ,.

allow_loading_unsigned_plugins = grafana-simple-json-backend-datasource,plesk-json-backend-datasource

Save the grafana.ini file and restart the Grafana server service:

systemctl restart grafana-server

Then reload the Plesk web interface. The monitoring panels will now display values again.