Metrics not flushing

[instil-richard]

Using Python 3.8 and aws-lambda-powertools==0.9.1

It could be that I'm not using metrics as their design intended however I would like to make use of them in the following pattern so metrics can be consumed by classes shared across my project which are imported into my lambdas as needed (so my lambdas handlers have few lines of code) e.g.

from aws_lambda_powertools.metrics import Metrics
from mynamespace.mypackage import MyClass

metrics = Metrics()

@metrics.log_metrics 
def handler(request, context):
 
    # passing metrics to my class that does all the work for the lambda: 
    return MyClass(metrics).do_stuff()

Adding metrics to MyClass might look something like this (using randint for demo purposes obviously):

class MyClass:
    def __init__(self, metrics):
        self.metrics = metrics

    def do_stuff(self):
        success = random.randint(0, 1)

        if success:
            self.metrics.add_metric(name="Success", unit=MetricUnit.Count, value=1)
            self.metrics.add_dimension(name='service', value='MyClass')
            return True
        else:
            self.metrics.add_metric(name="Failure", unit=MetricUnit.Count, value=1)
            self.metrics.add_dimension(name='service', value='MyClass')
            return False

Following this pattern the desired metrics are created correctly but on subsequent executions metrics are not flushed so subsequent executions will output both a 'Success' AND a 'Failure' metric from a single execution, so the print output in logs looks like this:

{
    "Success": 1,
    "Failure": 1,
    "_aws": {
        "Timestamp": 1590714776621,
        "CloudWatchMetrics": [
            {
                "Namespace": "richard",
                "Dimensions": [
                    [
                        "service"
                    ]
                ],
                "Metrics": [
                    {
                        "Name": "Success",
                        "Unit": "Count"
                    },
                    {
                        "Name": "Failure",
                        "Unit": "Count"
                    }
                ]
            }
        ]
    },
    "service": "MyClass"
}

Metrics are supposed to be flushed by the log_metrics decorator on each handler execution no? Would love to get your thoughts on this if it's a bug or if I'm not using them as intended.

[heitorlessa]

Hi @dotorg-richard - Thank you for reporting this.

That doesn't seem right, and more like a bug - It's as if the metric set isn't being cleaned up. I'll try reproducing this on my end, and update here.

[heitorlessa]

It's a bug indeed - I'll create a test, and publish a patched version today.

[heitorlessa]

I'm building wheels, and publishing a new patch release 0.9.4 shortly.

I also documented how to manually serialize, flush, and clear metrics for scenarios where you want to have full control of it (no use of log_metrics)

[heitorlessa]

Done - 0.9.4 is now live.

Let me know if that works for you @dotorg-richard

[instil-richard]

Thanks Heitor for being so responsive, I'm deep into a big refactor right now will get you feedback when I can afford the context switch :)

[instil-richard]

Tested it on v0.9.5 and the fix works, the behavior is as expected. Thanks again!!