fix(dynamo): adjusts DynamoTableGlobalSecondaryIndexMonitoring to respect localAlarmNamePrefixOverride (#629)

Fixes #628

This change passes the BaseMonitoringProps passed into
DynamoTableGlobalSecondaryIndexMonitoring along to the super class
constructor, which exposes `localAlarmNamePrefixOverride` to be consumed
by Monitoring.createAlarmFactory. Additionally, this changes the
construction of the alarm factory to use `createAlarmFactory` from the
parent class (thus using `localAlarmNamePrefixOverride`, rather than
that from the parent scope (MonitoringFacade, which doesn't have
`localAlarmNamePrefixOverride` available).

By doing so, we achieve the more expected behavior of having
`localAlarmNamePrefixOverride` influence the local portion of the alarm
name. By default, that portion is just the GSI name itself, and there
are cases where this can cause collisions (e.g. two GSIs with the same
name on different tables). Having `localAlarmNamePrefixOverride`
function as expected provides an escape hatch for this corner case
without changing the default naming behavior. (i.e. including table name
in the alarm name).

---

_By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license_

Author: haljarrett

lib/monitoring/aws-dynamo/DynamoTableGlobalSecondaryIndexMonitoring.ts

@@ -59,7 +59,7 @@ export class DynamoTableGlobalSecondaryIndexMonitoring extends Monitoring {
     scope: MonitoringScope,
     props: DynamoTableGlobalSecondaryIndexMonitoringProps,
   ) {
-    super(scope);
+    super(scope, props);
 
     const namingStrategy = new MonitoringNamingStrategy({
       ...props,
@@ -92,7 +92,7 @@ export class DynamoTableGlobalSecondaryIndexMonitoring extends Monitoring {
     this.indexThrottleCountMetric =
       metricFactory.metricThrottledIndexRequestCount();
 
-    const alarmFactory = scope.createAlarmFactory(
+    const alarmFactory = this.createAlarmFactory(
       namingStrategy.resolveAlarmFriendlyName(),
     );
     this.gsiAlarmFactory = new DynamoAlarmFactory(alarmFactory);

test/monitoring/aws-dynamo/DynamoTableGlobalSecondaryIndexMonitoring.test.ts

@@ -78,3 +78,63 @@ test("snapshot test: all alarms", () => {
   expect(numAlarmsCreated).toStrictEqual(2);
   expect(Template.fromStack(stack)).toMatchSnapshot();
 });
+
+test("test: localAlarmNamePrefixOverride is properly applied", () => {
+  const stack = new Stack();
+  const scope = new TestMonitoringScope(stack, "Scope");
+
+  const table = new Table(stack, "Table", {
+    tableName: "DummyTable",
+    partitionKey: {
+      name: "id",
+      type: AttributeType.STRING,
+    },
+  });
+
+  const customPrefix = "CustomPrefix";
+  const indexName = "non-existing-index";
+  const monitoring = new DynamoTableGlobalSecondaryIndexMonitoring(scope, {
+    table,
+    globalSecondaryIndexName: indexName,
+    localAlarmNamePrefixOverride: customPrefix,
+    addReadThrottledEventsCountAlarm: {
+      Warning: {
+        maxThrottledEventsThreshold: 5,
+      },
+    },
+  });
+
+  addMonitoringDashboardsToStack(stack, monitoring);
+
+  const template = Template.fromStack(stack);
+  const alarms = template.findResources("AWS::CloudWatch::Alarm");
+  const alarmLogicalIds = Object.keys(alarms);
+
+  expect(alarmLogicalIds.length).toStrictEqual(1);
+
+  const alarmNames = alarmLogicalIds.map(
+    (id) => alarms[id].Properties.AlarmName,
+  );
+
+  const alarmNameHasCustomPrefix = alarmNames.every((name) =>
+    name.includes(customPrefix),
+  );
+
+  const alarmIdHasCustomPrefix = alarmLogicalIds.every((id) =>
+    id.includes(customPrefix),
+  );
+
+  const alarmNameHasDefaultPrefix = alarmNames.some((name) =>
+    name.includes(indexName),
+  );
+
+  const alarmIdHasDefaultPrefix = alarmLogicalIds.some((id) =>
+    id.includes(indexName),
+  );
+
+  expect(alarmNameHasCustomPrefix).toBe(true);
+  expect(alarmIdHasCustomPrefix).toBe(true);
+  expect(alarmNameHasDefaultPrefix).toBe(false);
+  expect(alarmIdHasDefaultPrefix).toBe(false);
+  expect(Template.fromStack(stack)).toMatchSnapshot();
+});