in src/main/scala/com/gu/elasticsearchmonitor/CloudwatchMetrics.scala [68:74]
def buildMasterMetricData(clusterName: String, masterInformation: MasterInformation): List[MetricDatum] = {
val now = Date() // consistent timestamp across metrics
val defaultDimensions = List("Cluster" -> clusterName)
List(
metricDatum("NumberOfMasterNodes", masterInformation.numberOfMasterInstances, StandardUnit.Count, defaultDimensions, now),
metricDatum("NumberOfRespondingMastersNodes", masterInformation.numberOfRespondingMasters, StandardUnit.Count, defaultDimensions, now))
}