Bug: Unable to push metrics with multiple dimensions

[Euclidite]

Expected Behaviour

I expect to be able to push metrics with multiple dimensions either via PushSingleMetric or multiple calls to AddDimension.

Current Behaviour

When using any of the following:

Metrics.SetDefaultDimensions(new Dictionary<string, string> {
    { "SessionId", input.SessionId ?? "Unset" }
});

Metrics.PushSingleMetric("Lambda Execute", 1, MetricUnit.Count, metricResolution: MetricResolution.High,
    defaultDimensions: new Dictionary<string, string> {
        { "Type", "Start" }
});

Metrics.PushSingleMetric("Lambda Execute", 1, MetricUnit.Count, metricResolution: MetricResolution.High,
    defaultDimensions: new Dictionary<string, string> {
        { "Type", "Start" },
        { "SessionId", input.SessionId ?? "Unset" }
});

Metrics.AddMetric("Lambda Execute", 1, MetricUnit.Count, MetricResolution.High);
Metrics.AddDimension("SessionId", input.SessionId ?? "Unset");
Metrics.AddDimension("Type", "Start");

The following EMF is logged:

{
    "_aws": {
        "Timestamp": 1728338129260,
        "CloudWatchMetrics": [
            {
                "Namespace": "Services",
                "Metrics": [
                    {
                        "Name": "Lambda Execute",
                        "Unit": "Count",
                        "StorageResolution": 1
                    }
                ],
                "Dimensions": [
                    [
                        "SessionId"
                    ],
                    [
                        "Type"
                    ],
                    [
                        "Service"
                    ]
                ]
            }
        ]
    },
    "SessionId": "3da49fdb-aa91-4523-a6ea-a030817d2410",
    "Type": "Start",
    "Service": "coordinator",
    "Lambda Execute": 1
}

And the following appears in the CloudWatch console:

Essentially, it creates 3 different metrics for each dimension.

Code snippet

Metrics.AddMetric("Lambda Execute", 1, MetricUnit.Count, MetricResolution.High);
Metrics.AddDimension("SessionId", input.SessionId ?? "Unset");
Metrics.AddDimension("Type", "Start");

Possible Solution

No response

Steps to Reproduce

See code snippet

Powertools for AWS Lambda (.NET) version

latest

AWS Lambda function runtime

dotnet8

Debugging logs

No response

[boring-cyborg]

Thanks for opening your first issue here! We'll come back to you as soon as we can.
In the meantime, check out the #dotnet channel on our Powertools for AWS Lambda Discord: Invite link

[hjgraca]

@Euclidite thanks for reporting the issue, we are actively working on a fix.

[leandrodamascena]

Hello @hjgraca and @Euclidite! Yes, I agree the way the metric is being serialized today needs to be changed. Dimensions has to be a string array and not a list array, because in this case it will have the side effect of not aggregating the dimensions into a metric and creating 3 instead.

The official documentations says:

A DimensionSet is an array of strings containing the dimension keys that will be applied to all metrics in the document. The values within this array MUST also be members on the root-node—referred to as the Target members

The EMF BLOB should be:

"_aws": {
        "Timestamp": 1728338129260,
        "CloudWatchMetrics": [
            {
                "Namespace": "Services",
                "Metrics": [
                    {
                        "Name": "Lambda Execute",
                        "Unit": "Count",
                        "StorageResolution": 1
                    }
                ],
                "Dimensions": [
                    [
                        "SessionId",
                        "Type",
                        "Service"
                    ]
                ]
            }
        ]
    },
    "SessionId": "3da49fdb-aa91-4523-a6ea-a030817d2410",
    "Type": "Start",
    "Service": "coordinator",
    "Lambda Execute": 1
    }

[Euclidite]

Thank you for looking at this so quickly! I'll keep an eye on this in case you need me to test the fix or need any additional info.

[hjgraca]

@Euclidite thanks again for reporting the issue we have a fix ready to merge, if everything goes as planned we will be releasing tomorrow. I will keep you updated. #664