fix: cloudfront request metric is using an invalid statistic (#1771)

The `Requests` metric that CloudFront emits should use the `Sum`
statistic, not `Average`.

> See **Requests** in
https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/programming-cloudwatch-metrics.html#cloudfront-metrics-distribution-values

In addition, change the period of the CloudFront metrics in the overview
dashboard to 1 day (from 5 minutes):

- We usually like to talk about "requests per day" to asses usage, over
"requests per 5 minutes".
- It allows for easier trend detection when looking at a large window.

### Before

<img width="1189" height="150" alt="Screenshot 2025-07-30 at 9 36 52 PM"
src="https://github.com/user-attachments/assets/2db44fb7-f3a5-47b3-ac9c-3d57efacbf91"
/>

### After

<img width="1201" height="134" alt="Screenshot 2025-07-30 at 9 37 18 PM"
src="https://github.com/user-attachments/assets/ab806112-6408-416e-a26e-0f704c986218"
/>


----

*By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license*

---------

Signed-off-by: github-actions <[email protected]>
Co-authored-by: github-actions <[email protected]>

Author: iliapolo

src/__tests__/__snapshots__/construct-hub.test.ts.snap

@@ -133,15 +133,15 @@ test('It adds cloud front distribution to the dashboard when present', () => {
             {
               Ref: 'DistributionCFDistribution882A7313',
             },
-            '","Region","Global",{"region":"us-east-1"}],["AWS/CloudFront","4xxErrorRate","DistributionId","',
+            '","Region","Global",{"region":"us-east-1","period":86400,"stat":"Sum"}],["AWS/CloudFront","4xxErrorRate","DistributionId","',
             {
               Ref: 'DistributionCFDistribution882A7313',
             },
-            '","Region","Global",{"region":"us-east-1","yAxis":"right"}],["AWS/CloudFront","5xxErrorRate","DistributionId","',
+            '","Region","Global",{"region":"us-east-1","period":86400,"yAxis":"right"}],["AWS/CloudFront","5xxErrorRate","DistributionId","',
             {
               Ref: 'DistributionCFDistribution882A7313',
             },
-            '","Region","Global",{"region":"us-east-1","yAxis":"right"}]],"yAxis":{"left":{"label":"Requests count"},"right":{"label":"Request Percent","min":0,"max":100}}}}]}',
+            '","Region","Global",{"region":"us-east-1","period":86400,"yAxis":"right"}]],"yAxis":{"left":{"label":"Requests count"},"right":{"label":"Request Percent","min":0,"max":100}}}}]}',
           ],
         ],
       },

src/__tests__/devapp/__snapshots__/snapshot.test.ts.snap

@@ -15,6 +15,7 @@ import { IOverviewDashboard } from './api';
 import { SQSDLQWidget } from './sqs-dlq-widget';
 import { Inventory } from '../backend/inventory';
 import { RUNBOOK_URL } from '../runbook-url';
+import { Duration } from 'aws-cdk-lib';
 
 /**
  * Properties for OverviewDashboard
@@ -127,10 +128,12 @@ export class OverviewDashboard extends Construct implements IOverviewDashboard {
       this.dashboard.addWidgets(this.cloudFrontMetricWidget);
     }
 
+    // see https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/programming-cloudwatch-metrics.html#cloudfront-metrics-distribution-values
+
     const totalRequest = new Metric({
       metricName: 'Requests',
       namespace: 'AWS/CloudFront',
-      statistic: Statistic.AVERAGE,
+      statistic: Statistic.SUM,
       dimensionsMap: {
         DistributionId: distribution.distributionId,
         Region: 'Global',
@@ -160,9 +163,9 @@ export class OverviewDashboard extends Construct implements IOverviewDashboard {
       region: 'us-east-1', // global metric
     });
 
-    this.cloudFrontMetricWidget.addLeftMetric(totalRequest);
-    this.cloudFrontMetricWidget.addRightMetric(errorRate4xx);
-    this.cloudFrontMetricWidget.addRightMetric(errorRate5xx);
+    this.cloudFrontMetricWidget.addLeftMetric(totalRequest.with({ period: Duration.days(1) }));
+    this.cloudFrontMetricWidget.addRightMetric(errorRate4xx.with({ period: Duration.days(1) }));
+    this.cloudFrontMetricWidget.addRightMetric(errorRate5xx.with({ period: Duration.days(1) }));
   }
 
   private addCloudFrontMetricWidget() {