feat: allow registering medium severity alarms

src/__tests__/monitoring.test.ts

@@ -108,17 +108,24 @@ test('monitoring exposes a list of high severity alarms', () => {
   const alarm2 = topic
     .metricSMSMonthToDateSpentUSD()
     .createAlarm(stack, 'Alarm2', { threshold: 100, evaluationPeriods: 1 });
+  const alarm3 = topic
+    .metricSMSMonthToDateSpentUSD()
+    .createAlarm(stack, 'Alarm3', { threshold: 500, evaluationPeriods: 1 });
 
   // WHEN
   monitoring.addHighSeverityAlarm('My Alarm', alarm1);
   monitoring.addLowSeverityAlarm('My Other Alarm', alarm2);
+  monitoring.addMediumSeverityAlarm('My Third Alarm', alarm3);
 
   expect(monitoring.highSeverityAlarms.map((alarm) => alarm.alarmArn)).toEqual([
     alarm1.alarmArn,
   ]);
   expect(monitoring.lowSeverityAlarms.map((alarm) => alarm.alarmArn)).toEqual([
     alarm2.alarmArn,
   ]);
+  expect(
+    monitoring.mediumSeverityAlarms.map((alarm) => alarm.alarmArn)
+  ).toEqual([alarm3.alarmArn]);
 });
 
 test('web canaries can ping URLs and raise high severity alarms', () => {
@@ -230,3 +237,32 @@ test('high-severity alarm actions are registered', () => {
     AlarmActions: [highSeverity, highSeverityActionArn],
   });
 });
+
+test('medium-severity alarm actions are registered', () => {
+  // GIVEN
+  const stack = new Stack(undefined, 'TestStack');
+  const alarm = new Alarm(stack, 'Alarm', {
+    evaluationPeriods: 1,
+    metric: new Metric({
+      metricName: 'FakeMetricName',
+      namespace: 'FakeNamespace',
+    }),
+    threshold: 0,
+  });
+
+  const mediumSeverity = 'fake::arn::of::an::action';
+  const mediumSeverityActionArn = 'fake::arn::of::bound:alarm::action';
+  const mediumSeverityAction: IAlarmAction = {
+    bind: () => ({ alarmActionArn: mediumSeverityActionArn }),
+  };
+
+  // WHEN
+  new Monitoring(stack, 'Monitoring', {
+    alarmActions: { mediumSeverity, mediumSeverityAction },
+  }).addMediumSeverityAlarm('Alarm', alarm);
+
+  // THEN
+  Template.fromStack(stack).hasResourceProperties('AWS::CloudWatch::Alarm', {
+    AlarmActions: [mediumSeverity, mediumSeverityActionArn],
+  });
+});

src/api.ts

@@ -57,6 +57,23 @@ export interface AlarmActions {
    */
   readonly highSeverityAction?: IAlarmAction;
 
+  /**
+   * The ARN of the CloudWatch alarm action to take for alarms of medium-severity
+   * alarms.
+   *
+   * This must be an ARN that can be used with CloudWatch alarms.
+   * @see https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/AlarmThatSendsEmail.html#alarms-and-actions
+   */
+  readonly mediumSeverity?: string;
+
+  /**
+   * The CloudWatch alarm action to take for alarms of medium-severity alarms.
+   *
+   * This must be an ARN that can be used with CloudWatch alarms.
+   * @see https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/AlarmThatSendsEmail.html#alarms-and-actions
+   */
+  readonly mediumSeverityAction?: IAlarmAction;
+
   /**
    * The ARN of the CloudWatch alarm action to take for alarms of normal
    * severity.

src/construct-hub.ts

@@ -350,13 +350,13 @@ export class ConstructHub extends Construct implements iam.IGrantable {
     // Create an internal CodeArtifact repository if we run in network-controlled mode, or if a domain is provided.
     const codeArtifact =
       isolation === Isolation.NO_INTERNET_ACCESS ||
-      props.codeArtifactDomain != null
+        props.codeArtifactDomain != null
         ? new Repository(this, 'CodeArtifact', {
-            description: 'Proxy to npmjs.com for ConstructHub',
-            domainName: props.codeArtifactDomain?.name,
-            domainExists: props.codeArtifactDomain != null,
-            upstreams: props.codeArtifactDomain?.upstreams,
-          })
+          description: 'Proxy to npmjs.com for ConstructHub',
+          domainName: props.codeArtifactDomain?.name,
+          domainExists: props.codeArtifactDomain != null,
+          upstreams: props.codeArtifactDomain?.upstreams,
+        })
         : undefined;
     const { vpc, vpcEndpoints, vpcSubnets, vpcSecurityGroups } = this.createVpc(
       isolation,
@@ -557,6 +557,17 @@ export class ConstructHub extends Construct implements iam.IGrantable {
     return this.monitoring.highSeverityAlarms;
   }
 
+  /**
+   * Returns a list of all low-severity alarms from this ConstructHub instance.
+   * These do not necessitate immediate attention, as they do not have direct
+   * customer-visible impact, or handling is not time-sensitive. They indicate
+   * that something unusual (not necessarily bad) is happening.
+   */
+  public get mediumSeverityAlarms(): cw.IAlarm[] {
+    // Note: the array is already returned by-copy by Monitoring, so not copying again.
+    return this.monitoring.mediumSeverityAlarms;
+  }
+
   /**
    * Returns a list of all low-severity alarms from this ConstructHub instance.
    * These do not necessitate immediate attention, as they do not have direct
@@ -572,7 +583,7 @@ export class ConstructHub extends Construct implements iam.IGrantable {
    * Returns a list of all alarms configured by this ConstructHub instance.
    */
   public get allAlarms(): cw.IAlarm[] {
-    return [...this.highSeverityAlarms, ...this.lowSeverityAlarms];
+    return [...this.highSeverityAlarms, ...this.lowSeverityAlarms, ...this.mediumSeverityAlarms];
   }
 
   public get grantPrincipal(): iam.IPrincipal {

src/monitoring/api.ts

@@ -14,6 +14,15 @@ export interface IMonitoring {
    */
   addHighSeverityAlarm(title: string, alarm: AlarmBase): void;
 
+  /**
+   * Adds a medium-severity alarm. If this alarm goes off, the action specified in
+   * `mediumSeverityAlarmAction` is triggered.
+   *
+   * @param title a user-friendly title for the alarm (not currently used).
+   * @param alarm the alarm to be added.
+   */
+  addMediumSeverityAlarm(title: string, alarm: AlarmBase): void;
+
   /**
    * Adds a low-severity alarm. If this alarm goes off, the action specified in
    * `normalAlarmAction` is triggered.

src/monitoring/index.ts

@@ -27,6 +27,7 @@ export interface MonitoringProps {
 export class Monitoring extends Construct implements IMonitoring {
   private alarmActions?: AlarmActions;
   private _highSeverityAlarms: cw.AlarmBase[];
+  private _mediumSeverityAlarms: cw.AlarmBase[];
   private _lowSeverityAlarms: cw.AlarmBase[];
 
   /**
@@ -55,6 +56,7 @@ export class Monitoring extends Construct implements IMonitoring {
 
     this._highSeverityAlarms = [];
     this._lowSeverityAlarms = [];
+    this._mediumSeverityAlarms = [];
 
     this.highSeverityDashboard = new cw.Dashboard(
       this,
@@ -103,10 +105,28 @@ export class Monitoring extends Construct implements IMonitoring {
     this._lowSeverityAlarms.push(alarm);
   }
 
+  public addMediumSeverityAlarm(_title: string, alarm: cw.AlarmBase) {
+    const actionArn = this.alarmActions?.mediumSeverity;
+    if (actionArn) {
+      alarm.addAlarmAction({
+        bind: () => ({ alarmActionArn: actionArn }),
+      });
+    }
+    const action = this.alarmActions?.mediumSeverityAction;
+    if (action) {
+      alarm.addAlarmAction(action);
+    }
+    this._mediumSeverityAlarms.push(alarm);
+  }
+
   public get highSeverityAlarms() {
     return [...this._highSeverityAlarms];
   }
 
+  public get mediumSeverityAlarms() {
+    return [...this._mediumSeverityAlarms];
+  }
+
   public get lowSeverityAlarms() {
     return [...this._lowSeverityAlarms];
   }

test/integ.transliterator.ecstask.ts

@@ -24,6 +24,7 @@ const transliterator = new Transliterator(stack, 'Transliterator', {
   bucket,
   monitoring: {
     addHighSeverityAlarm: () => {},
+    addMediumSeverityAlarm: () => {},
     addLowSeverityAlarm: () => {},
   },
 });