The error "failed to connect to server" typically indicates that Grafana is unable to establish a connection to the PostgreSQL database. This could be due to various reasons, including incorrect database configuration, network issues, or database server errors.

Here are some steps to troubleshoot and resolve this issue:

Check PostgreSQL Server Status: Ensure that the PostgreSQL database server is running and accessible. You can verify the status of the PostgreSQL service using system management commands specific to your operating system (e.g., systemctl status postgresql on Linux).

Verify Database Configuration: Double-check the database configuration in the Grafana configuration file (grafana.ini). Ensure that the database hostname, port, username, password, and database name are correctly configured.

Test Database Connection: Try connecting to the PostgreSQL database using the same credentials and connection parameters configured in Grafana from a command-line interface or database client tool. This can help verify if the database server is reachable and if the credentials are correct.

Review Grafana Logs: Inspect the Grafana server logs for any error messages or warnings related to the database connection. The logs are typically located in the Grafana installation directory under the logs or data/log directory.

Firewall and Security Settings: Check for any firewall rules or security settings that may be blocking the connection between Grafana and PostgreSQL. Ensure that the necessary ports (e.g., default PostgreSQL port 5432) are open and accessible.

Database Permissions: Verify that the database user configured in Grafana has the necessary permissions to connect to the database and perform operations.

Database Configuration Changes: If you recently made changes to the database configuration in Grafana, ensure that those changes are correctly applied and that there are no syntax errors or typos.

Update Grafana and PostgreSQL: Make sure that you are using the latest versions of Grafana and PostgreSQL, as newer versions may include bug fixes and improvements related to database connectivity.