feat: Static anomaly detection for pr (#89)

* Create minimumViews parameter for anomaly detect

* Meet the prettier requirements

* Update docs/ANOMALY_DETECTION.md

Clarify verbiage on MINIMUM_VIEWS

Co-authored-by: Rehan van der Merwe <[email protected]>

* Update infra/src/index.ts

Clarify comment on min num views

Co-authored-by: Rehan van der Merwe <[email protected]>

---------

Co-authored-by: Rehan van der Merwe <[email protected]>

Author: kc0bfv

application/src/backend/cron-anomaly-detection/environment.ts

@@ -16,6 +16,7 @@ export class LambdaEnvironment {
   static EVALUATION_WINDOW: number;
   static BREACHING_MULTIPLIER: number;
   static EVENT_BRIDGE_SOURCE: string;
+  static MINIMUM_VIEWS: number;
 
   static init() {
     const schema = z.object({
@@ -32,6 +33,7 @@ export class LambdaEnvironment {
       EVALUATION_WINDOW: z.string().transform((v) => Number(v)),
       BREACHING_MULTIPLIER: z.string().transform((v) => Number(v)),
       EVENT_BRIDGE_SOURCE: z.string(),
+      MINIMUM_VIEWS: z.string().transform((v) => Number(v)),
     });
     const parsed = schema.safeParse(process.env);
 

application/src/backend/cron-anomaly-detection/stat_functions.ts

@@ -168,7 +168,8 @@ export function predict(data: CleanedData, seasonLength: number, predictedBreach
   const breachingThreshold = predicted * predictedBreachingMultiplier;
   /* Use the `data.latest.record` instead of `data.trainingDataViews[data.trainingDataViews.length-1]` because the
    * latter has clamped values */
-  const breachingLatest = latestRecord.views > breachingThreshold;
+  const breachingLatest =
+    latestRecord.views > LambdaEnvironment.MINIMUM_VIEWS && latestRecord.views > breachingThreshold;
   logger.debug('Prediction', {
     Latest: latestRecord,
     Predicted: predicted,

docs/ANOMALY_DETECTION.md

@@ -25,6 +25,7 @@ Two important environment variables are used to configure the detection:
    The actual value of 100 is less than the breaching threshold of 160, so the evaluation is not marked as breaching.
    If the actual value was say 200, then it would be more than the breaching threshold and the evaluation would be
    marked as breaching.
+- `MINIMUM_VIEWS` The minimum number of views before an evaluation is considered breached. Continuing with the example above, if the `Minimum Views` parameter is specified as 101, which is less than the actual view of 100, then the predicted value, breaching multiplier, and the breaching threshold are irrelevant as the evaluation will not be able to transition into the breaching state.
 
 ### Logic
 

infra/src/backend.ts

@@ -349,6 +349,7 @@ export function backend(
         EVALUATION_WINDOW: props.anomaly.detection.evaluationWindow!.toString(),
         BREACHING_MULTIPLIER: props.anomaly.detection.predictedBreachingMultiplier!.toString(),
         EVENT_BRIDGE_SOURCE: eventBridgeSource,
+        MINIMUM_VIEWS: props.anomaly.detection.minimumViews!.toString(),
       },
       /* The lambda is NOT idempotent */
       retryAttempts: 0,

infra/src/index.ts

@@ -180,6 +180,12 @@ export interface AnomalyDetectionProps {
    * @default 2
    */
   readonly predictedBreachingMultiplier?: number;
+
+  /**
+   * The minimum number of views before an evaluation is considered breached.
+   * @default 0
+   */
+  readonly minimumViews?: number;
 }
 
 export interface AnomalyAlertProps {
@@ -210,7 +216,8 @@ export interface AnomalyProps {
    * Optional, if specified overrides the default properties
    * @default ```{
    *   evaluationWindow: 2,
-   *   predictedBreachingMultiplier: 2
+   *   predictedBreachingMultiplier: 2,
+   *   minimumViews: 0
    * }```
    */
   readonly detection?: AnomalyDetectionProps;
@@ -346,6 +353,7 @@ export class Swa extends Construct {
         detection: {
           evaluationWindow: 2,
           predictedBreachingMultiplier: 2,
+          minimumViews: 0,
         },
         alert: {
           onAlarm: true,

tests/test-config.ts

@@ -31,6 +31,7 @@ export type TestConfig = {
     EVALUATION_WINDOW: string;
     BREACHING_MULTIPLIER: string;
     EVENT_BRIDGE_SOURCE: string;
+    MINIMUM_VIEWS: string;
 
     ALERT_TOPIC_ARN: string;
     ALERT_ON_ALARM: string;
@@ -83,6 +84,7 @@ export const TestConfig: TestConfig = {
     EVALUATION_WINDOW: '2',
     BREACHING_MULTIPLIER: '2',
     EVENT_BRIDGE_SOURCE: 'swa-demo-prod',
+    MINIMUM_VIEWS: '0',
 
     ALERT_TOPIC_ARN: 'arn:aws:sns:eu-west-1:123456789:your-topic-name',
     ALERT_ON_ALARM: 'true',