Nesting log_metrics only results in one set of metrics being logged

Expected Behaviour

When using two Metrics objects and two nested call to log_metrics I expected both sets of metrics to be serialized. The reason for two Metrics object is that every metric is output twice, with a different set of dimensions. Using single_metric for everything works but seems sub-optimal from a performance standpoint.

Example:

app = ...  # FastAPI app

# API handler metrics with dimensions: Stage, service
api_metrics = Metrics()
api_metrics.set_default_dimensions(Stage=os.environ['STAGE'])

# API handler metrics with dimensions: Method, Resource, Stage, service
detailed_api_metrics = Metrics()
detailed_api_metrics.set_default_dimensions(Stage=os.environ['STAGE'])

handler = Mangum(app)
handler = logging.getLogger().inject_lambda_context(handler, clear_state=True)
# Add metrics last to properly flush metrics.
handler = api_metrics.log_metrics(handler, capture_cold_start_metric=True)
handler = detailed_api_metrics.log_metrics(handler)

Current Behaviour

Looking in the CloudWatch logs only the JSON for one set of metrics (api_metrics above) is output.

Code snippet

from aws_lambda_powertools.metrics import Metrics, MetricUnit

# API handler metrics with dimensions: Stage, service
api_metrics = Metrics()
api_metrics.set_default_dimensions(Stage='Test')

# API handler metrics with dimensions: Method, Resource, Stage, service
detailed_api_metrics = Metrics()
detailed_api_metrics.set_default_dimensions(Stage='Test')

def handler(event, context):
    detailed_api_metrics.add_dimension(
        name='Method', value='GET')
    detailed_api_metrics.add_dimension(
        name='Resource', value='/some/path')

    api_metrics.add_metric(name='Count',
                           unit=MetricUnit.Count, value=1)
    detailed_api_metrics.add_metric(
        name='Count', unit=MetricUnit.Count, value=1)

# Add metrics last to properly flush metrics.
handler = api_metrics.log_metrics(handler, capture_cold_start_metric=True)
handler = detailed_api_metrics.log_metrics(handler)

Possible Solution

No response

Steps to Reproduce

• Run the above code on Lambda.
• Look in the logs.
• See that the JSON from one set of metrics is missing.

AWS Lambda Powertools for Python version

1.25.10

AWS Lambda function runtime

3.9

Packaging format used

PyPi

Debugging logs

I do see the two following things in the log:


/opt/python/aws_lambda_powertools/metrics/metrics.py:189: UserWarning: No metrics to publish, skipping
warnings.warn("No metrics to publish, skipping")

Note that the two Metrics objects are used unconditionally right after each other so it would be weird for one to have metrics and one to have not.

{
    "_aws": {
        "Timestamp": 1666944145372,
        "CloudWatchMetrics": [
            {
                "Namespace": "Benetics/Backend",
                "Dimensions": [
                    [
                        "Stage",
                        "service"
                    ]
                ],
                "Metrics": [
                    {
                        "Name": "Count",
                        "Unit": "Count"
                    },
                    {
                        "Name": "4xx",
                        "Unit": "Count"
                    },
                    {
                        "Name": "5xx",
                        "Unit": "Count"
                    },
                    {
                        "Name": "Latency",
                        "Unit": "Milliseconds"
                    }
                ]
            }
        ]
    },
    "Stage": "prod",
    "service": "Api",
    "Count": [
        1,
        1
    ],
    "4xx": [
        0,
        0
    ],
    "5xx": [
        0,
        0
    ],
    "Latency": [
        184,
        184
    ]
}

[tibbe]

@heitorlessa thanks! I’ve now integrated 2.2.0 in our backend and things seem to be working well so far!

[heitorlessa]

@tibbe this is now available as part of v2.2.0 release (Lambda Layer v13): https://github.com/awslabs/aws-lambda-powertools-python/releases/tag/v2.2.0

Let me know if that doesn’t address your original ask.