dimensions

The dimensions. If the metric contains multiple dimensions, you must include a value for each dimension. CloudWatch treats each unique combination of dimensions as a separate metric. If a specific combination of dimensions was not published, you can't retrieve statistics for it. You must specify the same dimensions that were used when the metrics were created. For an example, see Dimension Combinations in the Amazon CloudWatch User Guide. For more information about specifying dimensions, see Publishing Metrics in the Amazon CloudWatch User Guide.