feat(metrics): disable metrics with POWERTOOLS_METRICS_DISABLED (#3351)

Co-authored-by: Andrea Amorosi <[email protected]>

Author: zirkelc

Diff for: packages/commons/src/config/EnvironmentVariablesService.ts

@@ -93,6 +93,17 @@ class EnvironmentVariablesService implements ConfigServiceInterface {
     return truthyValues.includes(value.toLowerCase());
   }
 
+  /**
+   * Helper function to determine if a value is considered falsy.
+   *
+   * @param value The value to check for falsiness.
+   */
+  public isValueFalse(value: string): boolean {
+    const falsyValues: string[] = ['0', 'n', 'no', 'f', 'false', 'off'];
+
+    return falsyValues.includes(value.toLowerCase());
+  }
+
   /**
    * Get the AWS X-Ray Trace data from the environment variable.
    *

Diff for: packages/commons/tests/unit/EnvironmentVariablesService.test.ts

@@ -159,6 +159,37 @@ describe('Class: EnvironmentVariablesService', () => {
     );
   });
 
+  describe('Method: isValueFalse', () => {
+    const valuesToTest: Array<Array<string | boolean>> = [
+      ['0', true],
+      ['n', true],
+      ['no', true],
+      ['f', true],
+      ['FALSE', true],
+      ['off', true],
+      ['1', false],
+      ['y', false],
+      ['yes', false],
+      ['t', false],
+      ['TRUE', false],
+      ['on', false],
+      ['', false],
+      ['somethingsilly', false],
+    ];
+
+    it.each(valuesToTest)(
+      'takes string "%s" and returns %s',
+      (input, output) => {
+        // Prepare
+        const service = new EnvironmentVariablesService();
+        // Act
+        const value = service.isValueFalse(input as string);
+        // Assess
+        expect(value).toBe(output);
+      }
+    );
+  });
+
   describe('Method: isDevMode', () => {
     it('returns true if the environment variable POWERTOOLS_DEV is "true"', () => {
       // Prepare

Diff for: packages/metrics/src/Metrics.ts

@@ -201,6 +201,11 @@ class Metrics extends Utility implements MetricsInterface {
    */
   private storedMetrics: StoredMetrics = {};
 
+  /**
+   * Whether to disable metrics
+   */
+  private disabled = false;
+
   /**
    * Custom timestamp for the metrics
    */
@@ -472,6 +477,13 @@ class Metrics extends Utility implements MetricsInterface {
     return Object.keys(this.storedMetrics).length > 0;
   }
 
+  /**
+   * Whether metrics are disabled.
+   */
+  protected isDisabled(): boolean {
+    return this.disabled;
+  }
+
   /**
    * A class method decorator to automatically log metrics after the method returns or throws an error.
    *
@@ -579,8 +591,12 @@ class Metrics extends Utility implements MetricsInterface {
           'If application metrics should never be empty, consider using `throwOnEmptyMetrics`'
       );
     }
-    const emfOutput = this.serializeMetrics();
-    hasMetrics && this.console.log(JSON.stringify(emfOutput));
+
+    if (!this.disabled) {
+      const emfOutput = this.serializeMetrics();
+      hasMetrics && this.console.log(JSON.stringify(emfOutput));
+    }
+
     this.clearMetrics();
     this.clearDimensions();
     this.clearMetadata();
@@ -913,6 +929,15 @@ class Metrics extends Utility implements MetricsInterface {
       this.getEnvVarsService().getNamespace()) as string;
   }
 
+  /**
+   * Set the disbaled flag based on the environment variables `POWERTOOLS_METRICS_DISABLED` and `POWERTOOLS_DEV`.
+   *
+   * The `POWERTOOLS_METRICS_DISABLED` environment variable takes precedence over `POWERTOOLS_DEV`.
+   */
+  private setDisabled(): void {
+    this.disabled = this.getEnvVarsService().getMetricsDisabled();
+  }
+
   /**
    * Set the options to be used by the Metrics instance.
    *
@@ -932,6 +957,7 @@ class Metrics extends Utility implements MetricsInterface {
     this.setEnvVarsService();
     this.setConsole();
     this.setCustomConfigService(customConfigService);
+    this.setDisabled();
     this.setNamespace(namespace);
     this.setService(serviceName);
     this.setDefaultDimensions(defaultDimensions);

Diff for: packages/metrics/src/config/EnvironmentVariablesService.ts

@@ -13,12 +13,29 @@ class EnvironmentVariablesService
 {
   private namespaceVariable = 'POWERTOOLS_METRICS_NAMESPACE';
 
+  private readonly disabledVariable = 'POWERTOOLS_METRICS_DISABLED';
+
   /**
    * Get the value of the `POWERTOOLS_METRICS_NAMESPACE` environment variable.
    */
   public getNamespace(): string {
     return this.get(this.namespaceVariable);
   }
+
+  /**
+   * Get the value of the `POWERTOOLS_METRICS_DISABLED` or `POWERTOOLS_DEV` environment variables.
+   *
+   * The `POWERTOOLS_METRICS_DISABLED` environment variable takes precedence over `POWERTOOLS_DEV`.
+   */
+  public getMetricsDisabled(): boolean {
+    const value = this.get(this.disabledVariable);
+
+    if (this.isValueFalse(value)) return false;
+    if (this.isValueTrue(value)) return true;
+    if (this.isDevMode()) return true;
+
+    return false;
+  }
 }
 
 export { EnvironmentVariablesService };

Diff for: packages/metrics/tests/unit/Metrics.test.ts

@@ -1430,6 +1430,29 @@ describe('Class: Metrics', () => {
       expect(consoleLogSpy).toBeCalledWith(JSON.stringify(mockData));
     });
 
+    test('it should not log anything if metrics are disabled', () => {
+      // Prepare
+      process.env.POWERTOOLS_METRICS_DISABLED = 'true';
+      const customLogger = {
+        log: jest.fn(),
+        warn: jest.fn(),
+        debug: jest.fn(),
+        error: jest.fn(),
+        info: jest.fn(),
+      };
+      const metrics: Metrics = new Metrics({
+        namespace: TEST_NAMESPACE,
+        logger: customLogger,
+      });
+      const consoleLogSpy = jest.spyOn(customLogger, 'log');
+
+      // Act
+      metrics.publishStoredMetrics();
+
+      // Assess
+      expect(consoleLogSpy).toHaveBeenCalledTimes(0);
+    });
+
     test('it should call clearMetrics function', () => {
       // Prepare
       const metrics: Metrics = new Metrics({ namespace: TEST_NAMESPACE });
@@ -2355,6 +2378,54 @@ describe('Class: Metrics', () => {
     });
   });
 
+  describe('Method: isDisabled', () => {
+    it('should be enabled by default', () => {
+      const metrics: Metrics = new Metrics({ namespace: TEST_NAMESPACE });
+
+      // Act & Assess
+      // biome-ignore lint/complexity/useLiteralKeys: accessing protected method
+      expect(metrics['isDisabled']()).toBe(false);
+    });
+
+    it('should be disabled if POWERTOOLS_DEV is set to true', () => {
+      process.env.POWERTOOLS_DEV = 'true';
+      const metrics: Metrics = new Metrics({ namespace: TEST_NAMESPACE });
+
+      // Act & Assess
+      // biome-ignore lint/complexity/useLiteralKeys: accessing protected method
+      expect(metrics['isDisabled']()).toBe(true);
+    });
+
+    it('should be disabled if POWERTOOLS_METRICS_DISABLED is set to true', () => {
+      // Prepare
+      process.env.POWERTOOLS_METRICS_DISABLED = 'true';
+      const metrics: Metrics = new Metrics({ namespace: TEST_NAMESPACE });
+
+      // Act & Assess
+      // biome-ignore lint/complexity/useLiteralKeys: accessing protected method
+      expect(metrics['isDisabled']()).toBe(true);
+    });
+
+    it('should be enabled if POWERTOOLS_METRICS_DISABLED is set to false', () => {
+      process.env.POWERTOOLS_METRICS_DISABLED = 'false';
+      const metrics: Metrics = new Metrics({ namespace: TEST_NAMESPACE });
+
+      // Act & Assess
+      // biome-ignore lint/complexity/useLiteralKeys: accessing protected method
+      expect(metrics['isDisabled']()).toBe(false);
+    });
+
+    it('should be enabled if POWERTOOLS_DEV is set to true and POWERTOOLS_METRICS_DISABLED is set to false', () => {
+      process.env.POWERTOOLS_DEV = 'true';
+      process.env.POWERTOOLS_METRICS_DISABLED = 'false';
+      const metrics: Metrics = new Metrics({ namespace: TEST_NAMESPACE });
+
+      // Act & Assess
+      // biome-ignore lint/complexity/useLiteralKeys: accessing protected method
+      expect(metrics['isDisabled']()).toBe(false);
+    });
+  });
+
   describe('Method: setTimestamp', () => {
     const testCases = [
       {