If adding Promethus data source is failing, ensure to check the following two scenarios:
Verify that Prometheus's default port (9090) is accepted by the firewall.
If the port is blocked, it can prevent Grafana from establishing a connection to Prometheus. Consult your system's documentation or network administrator for instructions on how to open ports in the firewall.
Verify that the Prometheus service is running on the specified server.
Check the status of the Prometheus service to ensure the Prometheus service is up and running
journalctl -u prometheus.service
This command displays the logs related to the Prometheus service. Check for any errors or issues that may indicate why the service is not running correctly and fix them.