Support publishing Metrics with no dimensions

[kasikaruppiah]

configureContextForEnvironment sets LogGroup, ServiceName and ServiceType as defaultDimension when none is set

Code to reproduce the issue

final var metricsLogger = new MetricsLogger();
metricsLogger.putMetric("ErrorMetric", 0, Unit.NONE);
metricsLogger.flush();

Generated Log

{
    "_aws": {
        "Timestamp": 1599079576076,
        "CloudWatchMetrics": [
            {
                "Namespace": "Dummy",
                "Metrics": [
                    {
                        "Name": "ErrorMetric",
                        "Unit": "None"
                    }
                ],
                "Dimensions": [
                    [
                        "LogGroup",
                        "ServiceName",
                        "ServiceType"
                    ]
                ]
            }
        ]
    },
    "traceId": "Root=1-dc99d00f-c079a84d433534434534ef0d;Parent=91ed514f1e5c03b2;Sampled=1",
    "functionVersion": "$LATEST",
    "LogGroup": "test",
    "ServiceName": "test",
    "ServiceType": "AWS::Lambda::Function",
    "logStreamId": "2020/09/02/[$LATEST]fe81001002b19bc93650b6779072f274",
    "ErrorMetric": 0.0,
    "executionEnvironment": "AWS_Lambda_java11"
}

Ended up using metricsLogger.setDimensions(); to remove the defaultDimensions as a workaround.

{
    "_aws": {
        "Timestamp": 1599085078153,
        "CloudWatchMetrics": [
            {
                "Namespace": "Dummy",
                "Metrics": [
                    {
                        "Name": "ErrorMetric",
                        "Unit": "None"
                    }
                ],
                "Dimensions": []
            }
        ]
    },
    "traceId": "Root=1-dc99d00f-c079a84d433534434534ef0d;Parent=91ed514f1e5c03b2;Sampled=1",
    "logStreamId": "2020/09/02/[$LATEST]174dbe23d48fa649561c2941f408b34e",
    "ErrorMetric": 0.0,
    "functionVersion": "$LATEST",
    "executionEnvironment": "AWS_Lambda_java11"
}

The Embedded Metric Format schema supports metrics with no dimensions. Can we update the lib to get this fixed?

[yaozhaoy]

The current way to publish metrics with no dimensions is to call

logger.setDimensions()

There would be no dimensions carried over to subsequent flushes. You only need to call the setDimensions once for each.