Bug: metrics not flushing on throw

[flochaz]

Bug description

If using the decorator on handler and any execution flow endup throwing an exception, the metrics won't be flushed.

Expected Behavior

Metrics should be flushed whatever is happening in the customer code.

Current Behavior

If exception thrown, no metrics sent to cloudwatch.

Possible Solution

Option 1: Flush in a finally statement here: https://github.com/awslabs/aws-lambda-powertools-typescript/blob/main/packages/metrics/src/Metrics.ts#L93

Option 2: Leverage official lib https://github.com/awslabs/aws-embedded-metrics-node that handle this properly

Steps to Reproduce

Add this test to unit tests:

test('Using decorator should log even if exception thrown', async () => {
      const metrics = new Metrics({ namespace: 'test' });
      class LambdaFunction implements LambdaInterface {
        @metrics.logMetrics()
        // eslint-disable-next-line @typescript-eslint/ban-ts-comment
        // @ts-ignore
        public handler<TEvent, TResult>(
          _event: TEvent,
          _context: Context,
          _callback: Callback<TResult>
        ): void | Promise<TResult> {
          metrics.addMetric('test_name_1', MetricUnits.Count, 1);
          throw new Error('Test Error');
        }
      }

      try {
        await new LambdaFunction().handler(dummyEvent, dummyContext, () => console.log('Lambda invoked!'));
      } catch (error) {
        // DO NOTHING
      }
      
      expect(console.log).toBeCalledTimes(1);
    });

Should pass after fix

Environment

• Powertools version used: v0.0.1-alpha.3
• Packaging format (Layers, npm): npm
• AWS Lambda function runtime: nodejs
• Debugging logs: N/A

Related issues, RFCs

N/A

[github-actions]

⚠️ COMMENT VISIBILITY WARNING ⚠️

Comments on closed issues are hard for our team to see.
If you need more assistance, please either tag a team member or open a new issue that references this one.
If you wish to keep having a conversation with other community members under this issue feel free to do so.