Octavia CLI, as described in the [tutorial](https://airbyte.com/tutorials/version-control-airbyte-configurations), manages Airbyte resource configurations (sources, destinations, and connections) and provides commands to import, edit, and apply these configurations. When you apply a configuration using Octavia, it targets your Airbyte instance and checks if the resource exists. If it doesn't, Octavia creates it. If it does exist, Octavia updates the existing configuration with the new one. Here's an example of applying a configuration with Octavia:

bash octavia apply -f connections/postgres_to_bigquery/configuration.yaml

As for the diff functionality, Octavia doesn't explicitly provide a diff between the existing and new configurations. However, you can infer the changes by comparing the current configuration (before applying the new one) and the new configuration. For a potential workaround using the Airbyte API, you could: 1. Retrieve the current configuration using the Airbyte API. 2. Store this configuration locally. 3. Compare this stored configuration with your new configuration using a diff tool or custom code. 4. Apply the new configuration using the Airbyte API. Unfortunately, the specific API endpoints to retrieve and update configurations are not mentioned in the provided extracts. You would need to refer to the [Airbyte API documentation](https://docs.airbyte.com/api-documentation) for more details. Please note that this is a high-level approach and the actual implementation would depend on your specific use case and technical environment.