Monitoring: Could not find plugin definition for data source

If the Plesk extension "Monitoring" does not display any content, the Grafana service must be adapted.

The Grafana logs show that the plugin plesk-json-backend-datasource cannot be loaded due to the 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 under /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 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 only separated with a ,.

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

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

systemctl restart grafana-server

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