Base cold start heuristic on request id

Author: okoskine

Diff for: packages/logger/src/Logger.ts

@@ -106,9 +106,7 @@ import type {
  */
 class Logger implements ClassThatLogs {
 
-  private static coldStart?: boolean = undefined;
-
-  private static coldStartEvaluated: boolean = false;
+  private static coldStartRequestId?: string;
 
   private customConfigService?: ConfigServiceInterface;
 
@@ -152,10 +150,9 @@ class Logger implements ClassThatLogs {
    * @returns {void}
    */
   public addContext(context: Context): void {
-    Logger.evaluateColdStartOnce();
     const lambdaContext: Partial<LambdaFunctionContext> = {
       invokedFunctionArn: context.invokedFunctionArn,
-      coldStart: Logger.getColdStartValue(),
+      coldStart: Logger.getColdStartValue(context.awsRequestId),
       awsRequestId: context.awsRequestId,
       memoryLimitInMB: Number(context.memoryLimitInMB),
       functionName: context.functionName,
@@ -187,6 +184,15 @@ class Logger implements ClassThatLogs {
     this.addPersistentLogAttributes(attributes);
   }
 
+  /**
+   * Clears the static field that's used for checking if the request involved a cold start.
+   * @static
+   * @returns {void}
+   */
+  public static clearColdStartRequestId(): void {
+    Logger.coldStartRequestId = undefined;
+  }
+
   /**
    * It creates a separate Logger instance, identical to the current one
    * It's possible to overwrite the new instance options by passing them.
@@ -224,32 +230,13 @@ class Logger implements ClassThatLogs {
    * It evaluates whether the current Lambda function invocation has a cold start or not.
    *
    * @static
-   * @returns {void}
-   */
-  public static evaluateColdStartOnce(): void {
-    if (!Logger.getColdStartEvaluatedValue()) {
-      Logger.evaluateColdStart();
-    }
-  }
-
-  /**
-   * It returns a boolean value which is true if the current Lambda function cold start has been already evaluated, false otherwise.
-   *
-   * @static
    * @returns {boolean}
    */
-  public static getColdStartEvaluatedValue(): boolean {
-    return Logger.coldStartEvaluated;
-  }
+  public static getColdStartValue(currentRequestId: string): boolean {
+    if (!Logger.coldStartRequestId)
+      Logger.coldStartRequestId = currentRequestId;
 
-  /**
-   * It returns an optional boolean value, true if the current Lambda function invocation has a cold start, false otherwise.
-   *
-   * @static
-   * @returns {boolean | undefined}
-   */
-  public static getColdStartValue(): boolean | undefined {
-    return Logger.coldStart;
+    return currentRequestId === Logger.coldStartRequestId;
   }
 
   /**
@@ -305,30 +292,6 @@ class Logger implements ClassThatLogs {
     this.setLogsSampled();
   }
 
-  /**
-   * It sets the value of a flag static propriety that tracks whether
-   * the cold start evaluation already took place.
-   *
-   * @param {boolean} value
-   * @static
-   * @returns {void}
-   */
-  public static setColdStartEvaluatedValue(value: boolean): void {
-    Logger.coldStartEvaluated = value;
-  }
-
-  /**
-   * It sets the value of a flag static propriety that tracks whether
-   * the current Lambda invocation experienced a cold start.
-   *
-   * @static
-   * @param {boolean | undefined} value
-   * @returns {void}
-   */
-  public static setColdStartValue(value: boolean | undefined): void {
-    Logger.coldStart = value;
-  }
-
   /**
    * It sets the user-provided sample rate value.
    *
@@ -402,27 +365,6 @@ class Logger implements ClassThatLogs {
     return logItem;
   }
 
-  /**
-   * It evaluates whether the current Lambda invocation experienced a
-   * cold start.
-   *
-   * @private
-   * @static
-   * @returns {void}
-   */
-  private static evaluateColdStart(): void {
-    const coldStartValue = Logger.getColdStartValue();
-    if (typeof coldStartValue === 'undefined') {
-      Logger.setColdStartValue(true);
-    } else if (coldStartValue) {
-      Logger.setColdStartValue(false);
-    } else {
-      Logger.setColdStartValue(false);
-    }
-
-    Logger.setColdStartEvaluatedValue(true);
-  }
-
   /**
    * It returns the custom config service, an abstraction used to fetch environment variables.
    *

Diff for: packages/logger/tests/unit/Logger.test.ts

@@ -28,8 +28,7 @@ const consoleSpy = {
 describe('Class: Logger', () => {
 
   beforeEach(() => {
-    Logger.setColdStartValue(undefined);
-    Logger.setColdStartEvaluatedValue(false);
+    Logger.clearColdStartRequestId();
     consoleSpy['debug'].mockClear();
     consoleSpy['info'].mockClear();
     consoleSpy['warn'].mockClear();
@@ -647,55 +646,6 @@ describe('Class: Logger', () => {
 
   });
 
-  describe('Method: evaluateColdStartOnce', () => {
-
-    test('when called during the first invocation (cold start), it populates the logger\'s PowertoolLogData object with coldstart set to true', () => {
-
-      // Prepare
-      // This value is undefined at the beginning of the first invocation
-      Logger.setColdStartValue(undefined);
-
-      // Act
-      Logger.evaluateColdStartOnce();
-      Logger.evaluateColdStartOnce();
-      Logger.evaluateColdStartOnce();
-
-      // Assess
-      expect(Logger.getColdStartValue()).toEqual(true);
-    });
-
-    test('when called during the SECOND invocation (warm start), it populates the logger\'s PowertoolLogData object with coldstart set to false', () => {
-
-      // Prepare
-      // This value is set to true at the beginning of the second invocation
-      Logger.setColdStartValue(true);
-
-      // Act
-      Logger.evaluateColdStartOnce();
-      Logger.evaluateColdStartOnce();
-      Logger.evaluateColdStartOnce();
-
-      // Assess
-      expect(Logger.getColdStartValue()).toEqual(false);
-    });
-
-    test('when called during the THIRD invocation (warm start), it populates the logger\'s PowertoolLogData object with coldstart set to false', () => {
-
-      // Prepare
-      // This value is set to false at the beginning of the third invocation
-      Logger.setColdStartValue(false);
-
-      // Act
-      Logger.evaluateColdStartOnce();
-      Logger.evaluateColdStartOnce();
-      Logger.evaluateColdStartOnce();
-
-      // Assess
-      expect(Logger.getColdStartValue()).toEqual(false);
-    });
-
-  });
-
   describe('Method: injectLambdaContext', () => {
 
     beforeEach(() => {
@@ -834,29 +784,6 @@ describe('Class: Logger', () => {
 
   });
 
-  describe('Method: setColdStartValue', () => {
-
-    test('when called, it sets the value of the static variable coldStart in the same file', async () => {
-
-      // Act
-      Logger.setColdStartValue(undefined);
-      const undefinedValue = Logger.getColdStartValue();
-
-      Logger.setColdStartValue(true);
-      const trueValue = Logger.getColdStartValue();
-
-      Logger.setColdStartValue(false);
-      const falseValue = Logger.getColdStartValue();
-
-      // Assess
-      expect(undefinedValue).toBe(undefined);
-      expect(trueValue).toBe(true);
-      expect(falseValue).toBe(false);
-
-    });
-
-  });
-
   describe('Method: refreshSampleRateCalculation', () => {
 
     test('when called, it recalculates whether the current Lambda invocation\'s logs will be printed or not', () => {

Diff for: packages/logger/tests/unit/middleware/middy.test.ts

@@ -19,6 +19,7 @@ describe('Middy middleware', () => {
     // eslint-disable-next-line @typescript-eslint/no-empty-function
     jest.spyOn(console, 'log').mockImplementation(() => {});
     process.env = { ...ENVIRONMENT_VARIABLES };
+    Logger.clearColdStartRequestId();
   });
 
   afterAll(() => {