cloudwatch AWS/ECS returns wrong CPUUtilization metrics when both dimensions, ClusterName and ServiceName are set. It does return correctly when dimension is only ClusterName.

gistfile1.txt

$ aws cloudwatch get-metric-statistics --namespace AWS/ECS --metric-name CPUUtilization  --period 180 --statistics Average --dimensions Name=ClusterName,Value=jet-production Name=ServiceName,Value=jet-production --start-time 2016-07-14T10:15:00 --end-time 2016-07-14T11:00:00
{
    "Datapoints": [
        {
            "Timestamp": "2016-07-14T10:48:00Z",
            "Average": 81675.18434092174,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:39:00Z",
            "Average": 103709.39114214522,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:51:00Z",
            "Average": 19.330512713270576,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:18:00Z",
            "Average": 16.2821569693716,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:27:00Z",
            "Average": 37230.54646701979,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:57:00Z",
            "Average": 18.988085901528077,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:54:00Z",
            "Average": 18.80328689123455,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:24:00Z",
            "Average": 17.175868162634778,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:30:00Z",
            "Average": 104176.17951806249,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:45:00Z",
            "Average": 104851.72961204791,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:15:00Z",
            "Average": 16.909794673585054,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:36:00Z",
            "Average": 104887.60920090285,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:33:00Z",
            "Average": 105251.61943050016,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:21:00Z",
            "Average": 41.90878309540742,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:42:00Z",
            "Average": 103630.95255462469,
            "Unit": "Percent"
        }
    ],
    "Label": "CPUUtilization"
}

gistfile2.txt

$ aws cloudwatch get-metric-statistics --namespace AWS/ECS --metric-name CPUUtilization  --period 180 --statistics Average --dimensions Name=ClusterName,Value=jet-production --start-time 2016-07-14T10:15:00 --end-time 2016-07-14T11:00:00
{
    "Datapoints": [
        {
            "Timestamp": "2016-07-14T10:48:00Z",
            "Average": 40.0651929788911,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:39:00Z",
            "Average": 50.83104127746113,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:51:00Z",
            "Average": 0.16231633914084506,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:18:00Z",
            "Average": 0.08878160775666348,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:27:00Z",
            "Average": 18.335167804843206,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:57:00Z",
            "Average": 0.15746615980602038,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:54:00Z",
            "Average": 0.1568291576746688,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:24:00Z",
            "Average": 0.1466204669430024,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:30:00Z",
            "Average": 51.05638192994016,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:45:00Z",
            "Average": 51.388086287679876,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:15:00Z",
            "Average": 0.13577438407027495,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:36:00Z",
            "Average": 52.023197701320214,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:33:00Z",
            "Average": 51.58542941101794,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:21:00Z",
            "Average": 1.6066724619559898,
            "Unit": "Percent"
        },
        {
            "Timestamp": "2016-07-14T10:42:00Z",
            "Average": 50.793050104675935,
            "Unit": "Percent"
        }
    ],
    "Label": "CPUUtilization"
}