feat(metrics): allow setting functionName via constructor parameter and environment variable

docs/core/metrics.md

@@ -66,11 +66,12 @@ The library requires two settings. You can set them as environment variables, or
 
 These settings will be used across all metrics emitted:
 
-| Setting              | Description                                                      | Environment variable           | Default             | Allowed Values | Example             | Constructor parameter |
-| -------------------- | ---------------------------------------------------------------- | ------------------------------ | ------------------- | -------------- | ------------------- | --------------------- |
-| **Service**          | Optionally, sets **service** metric dimension across all metrics | `POWERTOOLS_SERVICE_NAME`      | `service_undefined` | Any string     | `serverlessAirline` | `serviceName`         |
-| **Metric namespace** | Logical container where all metrics will be placed               | `POWERTOOLS_METRICS_NAMESPACE` | `default_namespace` | Any string     | `serverlessAirline` | `default_namespace`   |
-| **Enabled**          | Whether to emit metrics to standard output or not                | `POWERTOOLS_METRICS_ENABLED`   | `true`              | Boolean        | `false`             |                       |
+| Setting              | Description                                                      | Environment variable               | Default                                                  | Allowed Values | Example             | Constructor parameter |
+|----------------------|------------------------------------------------------------------|------------------------------------|----------------------------------------------------------|----------------|---------------------|-----------------------|
+| **Service**          | Optionally, sets **service** metric dimension across all metrics | `POWERTOOLS_SERVICE_NAME`          | `service_undefined`                                      | Any string     | `serverlessAirline` | `serviceName`         |
+| **Metric namespace** | Logical container where all metrics will be placed               | `POWERTOOLS_METRICS_NAMESPACE`     | `default_namespace`                                      | Any string     | `serverlessAirline` | `default_namespace`   |
+| **Function Name**    | Function name used as dimension for the `ColdStart` metric       | `POWERTOOLS_METRICS_FUNCTION_NAME` | [See docs](#capturing-a-cold-start-invocation-as-metric) | Any string     | `my-function-name`  | `functionName`        |
+| **Enabled**          | Whether to emit metrics to standard output or not                | `POWERTOOLS_METRICS_ENABLED`       | `true`                                                   | Boolean        | `false`             |                       |
 
 !!! tip
     Use your application name or main service as the metric namespace to easily group all metrics
@@ -87,7 +88,7 @@ The `Metrics` utility is instantiated outside of the Lambda handler. In doing th
 
 === "template.yml"
 
-    ```yaml hl_lines="9 10"
+    ```yaml hl_lines="8-10"
     Resources:
       HelloWorldFunction:
         Type: AWS::Serverless::Function
@@ -97,6 +98,7 @@ The `Metrics` utility is instantiated outside of the Lambda handler. In doing th
           Variables:
             POWERTOOLS_SERVICE_NAME: orders
             POWERTOOLS_METRICS_NAMESPACE: serverlessAirline
+            POWERTOOLS_METRICS_FUNCTION_NAME: my-function-name
     ```
 
 You can initialize Metrics anywhere in your code - It'll keep track of your aggregate metrics in memory.
@@ -184,7 +186,7 @@ You can call `addMetric()` with the same name multiple times. The values will be
 
 ### Adding default dimensions
 
-You can add default dimensions to your metrics by passing them as parameters in 4 ways:  
+You can add default dimensions to your metrics by passing them as parameters in 4 ways:
 
 * in the constructor
 * in the [Middy-compatible](https://github.com/middyjs/middy){target=_blank} middleware
@@ -405,6 +407,28 @@ This has the advantage of keeping cold start metric separate from your applicati
 
 !!! info "We do not emit 0 as a value for the ColdStart metric for cost-efficiency reasons. [Let us know](https://github.com/aws-powertools/powertools-lambda-typescript/issues/new?assignees=&labels=feature-request%2C+triage&template=feature_request.md&title=) if you'd prefer a flag to override it."
 
+#### Setting function name
+
+When emitting cold start metrics, the `function_name` dimension defaults to `context.functionName`. If you want to change the value you can set the `functionName` parameter in the metrics constructor, define the environment variable `POWERTOOLS_METRICS_FUNCTION_NAME`, or pass a value to `captureColdStartMetric`.
+
+The priority of the `function_name` dimension value is defined as:
+
+1. `functionName` constructor option
+2. `POWERTOOLS_METRICS_FUNCTION_NAME` environment variable
+3. The value passed in the `captureColdStartMetric` call, or `context.functionName` if using logMetrics decorator or Middy middleware
+
+=== "constructor"
+
+    ```typescript hl_lines="6"
+    --8<-- "examples/snippets/metrics/functionName.ts"
+    ```
+
+=== "captureColdStartMetric method"
+
+    ```typescript hl_lines="12"
+    --8<-- "examples/snippets/metrics/captureColdStartMetric.ts"
+    ```
+
 ## Advanced
 
 ### Adding metadata

docs/index.md

@@ -351,22 +351,23 @@ Core utilities such as Tracing, Logging, and Metrics will be available across al
 ???+ info
     Explicit parameters take precedence over environment variables
 
-| Environment variable                         | Description                                                                                                   | Utility                                 | Default             |
-| -------------------------------------------- | ------------------------------------------------------------------------------------------------------------- | --------------------------------------- | ------------------- |
-| **POWERTOOLS_SERVICE_NAME**                  | Set service name used for tracing namespace, metrics dimension and structured logging                         | All                                     | `service_undefined` |
-| **POWERTOOLS_METRICS_NAMESPACE**             | Set namespace used for metrics                                                                                | [Metrics](core/metrics.md)              | `default_namespace` |
-| **POWERTOOLS_METRICS_ENABLED**               | Explicitly disables emitting metrics to stdout                                                                | [Metrics](core/metrics.md)              | `true`              |
-| **POWERTOOLS_TRACE_ENABLED**                 | Explicitly disables tracing                                                                                   | [Tracer](core/tracer.md)                | `true`              |
-| **POWERTOOLS_TRACER_CAPTURE_RESPONSE**       | Capture Lambda or method return as metadata.                                                                  | [Tracer](core/tracer.md)                | `true`              |
-| **POWERTOOLS_TRACER_CAPTURE_ERROR**          | Capture Lambda or method exception as metadata.                                                               | [Tracer](core/tracer.md)                | `true`              |
-| **POWERTOOLS_TRACER_CAPTURE_HTTPS_REQUESTS** | Capture HTTP(s) requests as segments.                                                                         | [Tracer](core/tracer.md)                | `true`              |
-| **POWERTOOLS_LOGGER_LOG_EVENT**              | Log incoming event                                                                                            | [Logger](core/logger.md)                | `false`             |
-| **POWERTOOLS_LOGGER_SAMPLE_RATE**            | Debug log sampling                                                                                            | [Logger](core/logger.md)                | `0`                 |
-| **POWERTOOLS_DEV**                           | Increase JSON indentation to ease debugging when running functions locally or in a non-production environment | [Logger](core/logger.md)                | `false`             |
-| **POWERTOOLS_LOG_LEVEL**                     | Sets how verbose Logger should be, from the most verbose to the least verbose (no logs)                       | [Logger](core/logger.md)                | `INFO`              |
-| **POWERTOOLS_PARAMETERS_MAX_AGE**            | Adjust how long values are kept in cache (in seconds)                                                         | [Parameters](utilities/parameters.md)   | `5`                 |
-| **POWERTOOLS_PARAMETERS_SSM_DECRYPT**        | Set whether to decrypt or not values retrieved from AWS Systems Manager Parameters Store                      | [Parameters](utilities/parameters.md)   | `false`             |
-| **POWERTOOLS_IDEMPOTENCY_DISABLED**          | Disable the Idempotency logic without changing your code, useful for testing                                  | [Idempotency](utilities/idempotency.md) | `false`             |
+| Environment variable                         | Description                                                                              | Utility                                 | Default                                         |
+| -------------------------------------------- |------------------------------------------------------------------------------------------| --------------------------------------- |-------------------------------------------------|
+| **POWERTOOLS_SERVICE_NAME**                  | Set service name used for tracing namespace, metrics dimension and structured logging    | All                                     | `service_undefined`                             |
+| **POWERTOOLS_METRICS_NAMESPACE**             | Set namespace used for metrics                                                           | [Metrics](core/metrics.md)              | `default_namespace`                             |
+| **POWERTOOLS_METRICS_FUNCTION_NAME**         | Function name used as dimension for the `ColdStart` metric                               | [Metrics](core/metrics.md)              | [See docs](core/metrics/#setting-function-name) |
+| **POWERTOOLS_METRICS_ENABLED**               | Explicitly disables emitting metrics to stdout                                           | [Metrics](core/metrics.md)              | `true`                                          |
+| **POWERTOOLS_TRACE_ENABLED**                 | Explicitly disables tracing                                                              | [Tracer](core/tracer.md)                | `true`                                          |
+| **POWERTOOLS_TRACER_CAPTURE_RESPONSE**       | Capture Lambda or method return as metadata.                                             | [Tracer](core/tracer.md)                | `true`                                          |
+| **POWERTOOLS_TRACER_CAPTURE_ERROR**          | Capture Lambda or method exception as metadata.                                          | [Tracer](core/tracer.md)                | `true`                                          |
+| **POWERTOOLS_TRACER_CAPTURE_HTTPS_REQUESTS** | Capture HTTP(s) requests as segments.                                                    | [Tracer](core/tracer.md)                | `true`                                          |
+| **POWERTOOLS_LOGGER_LOG_EVENT**              | Log incoming event                                                                       | [Logger](core/logger.md)                | `false`                                         |
+| **POWERTOOLS_LOGGER_SAMPLE_RATE**            | Debug log sampling                                                                       | [Logger](core/logger.md)                | `0`                                             |
+| **POWERTOOLS_DEV**                           | Pretty-print logs, disable metrics flushing, and disable traces - use for dev only       | See section below                       | `false`                                         |
+| **POWERTOOLS_LOG_LEVEL**                     | Sets how verbose Logger should be, from the most verbose to the least verbose (no logs)  | [Logger](core/logger.md)                | `INFO`                                          |
+| **POWERTOOLS_PARAMETERS_MAX_AGE**            | Adjust how long values are kept in cache (in seconds)                                    | [Parameters](utilities/parameters.md)   | `5`                                             |
+| **POWERTOOLS_PARAMETERS_SSM_DECRYPT**        | Set whether to decrypt or not values retrieved from AWS Systems Manager Parameters Store | [Parameters](utilities/parameters.md)   | `false`                                         |
+| **POWERTOOLS_IDEMPOTENCY_DISABLED**          | Disable the Idempotency logic without changing your code, useful for testing             | [Idempotency](utilities/idempotency.md) | `false`                                         |
 
 Each Utility page provides information on example values and allowed values.
 

examples/snippets/metrics/captureColdStartMetric.ts

@@ -0,0 +1,17 @@
+import { MetricUnit, Metrics } from '@aws-lambda-powertools/metrics';
+
+const metrics = new Metrics({
+  namespace: 'serverlessAirline',
+  serviceName: 'orders',
+});
+
+export const handler = async (
+  _event: unknown,
+  _context: unknown
+): Promise<void> => {
+  metrics.captureColdStartMetric('my-function-name');
+
+  metrics.addMetric('successfulBooking', MetricUnit.Count, 1);
+
+  metrics.publishStoredMetrics();
+};

examples/snippets/metrics/functionName.ts

@@ -0,0 +1,18 @@
+import { MetricUnit, Metrics } from '@aws-lambda-powertools/metrics';
+
+const metrics = new Metrics({
+  namespace: 'serverlessAirline',
+  serviceName: 'orders',
+  functionName: 'my-function-name',
+});
+
+export const handler = async (
+  _event: unknown,
+  _context: unknown
+): Promise<void> => {
+  metrics.captureColdStartMetric();
+
+  metrics.addMetric('successfulBooking', MetricUnit.Count, 1);
+
+  metrics.publishStoredMetrics();
+};

packages/metrics/src/Metrics.ts

@@ -371,8 +371,10 @@ class Metrics extends Utility implements MetricsInterface {
    *   metrics.captureColdStartMetric();
    * };
    * ```
+   *
+   * @param functionName - Optional function name to use as `function_name` dimension in the metric. It's used only if the `functionName` constructor parameter or environment variable are not set.
    */
-  public captureColdStartMetric(): void {
+  public captureColdStartMetric(functionName?: string): void {
     if (!this.getColdStart()) return;
     const singleMetric = this.singleMetric();
 
@@ -381,8 +383,11 @@ class Metrics extends Utility implements MetricsInterface {
         service: this.defaultDimensions.service,
       });
     }
-    if (this.functionName != null) {
-      singleMetric.addDimension('function_name', this.functionName);
+    for (const value of [this.functionName, functionName]) {
+      if (value && value.trim().length > 0) {
+        singleMetric.addDimension('function_name', value);
+        break;
+      }
     }
     singleMetric.addMetric(COLD_START_METRIC, MetricUnits.Count, 1);
   }
@@ -543,8 +548,9 @@ class Metrics extends Utility implements MetricsInterface {
         context: Context,
         callback: Callback
       ): Promise<unknown> {
-        metricsRef.functionName = context.functionName;
-        if (captureColdStartMetric) metricsRef.captureColdStartMetric();
+        if (captureColdStartMetric) {
+          metricsRef.captureColdStartMetric(context.functionName);
+        }
 
         let result: unknown;
         try {
@@ -749,28 +755,14 @@ class Metrics extends Utility implements MetricsInterface {
   }
 
   /**
-   * Set the function name to be added to each metric as a dimension.
-   *
-   * When using the {@link Metrics.logMetrics | `logMetrics()`} decorator, or the Middy.js middleware, the function
-   * name is automatically inferred from the Lambda context.
-   *
-   * @example
-   * ```typescript
-   * import { Metrics } from '@aws-lambda-powertools/metrics';
-   *
-   * const metrics = new Metrics({
-   *   namespace: 'serverlessAirline',
-   *   serviceName: 'orders'
-   * });
-   *
-   * metrics.setFunctionName('my-function-name');
-   * ```
-   *
-   * @param name - The function name
+   * @deprecated Override the function name for `ColdStart` metrics inferred from the context either via:
+   * - `functionName` constructor parameter
+   * - `POWERTOOLS_FUNCTION_NAME` environment variable
+   * - {@link Metrics.captureColdStartMetric | `captureColdStartMetric('myFunctionName')`} method
    */
-  public setFunctionName(name: string): void {
+  /* v8 ignore start */ public setFunctionName(name: string): void {
     this.functionName = name;
-  }
+  } /* v8 ignore end */
 
   /**
    * Set the flag to throw an error if no metrics are emitted.
@@ -917,6 +909,22 @@ class Metrics extends Utility implements MetricsInterface {
     this.envVarsService = new EnvironmentVariablesService();
   }
 
+  /**
+   * Set the function name for the cold start metric.
+   *
+   * @param functionName - The function name to be used for the cold start metric set in the constructor
+   */
+  protected setFunctionNameForColdStartMetric(functionName?: string): void {
+    const constructorFunctionName = functionName;
+    const envFunctionName = this.getEnvVarsService().getFunctionName();
+    for (const value of [constructorFunctionName, envFunctionName]) {
+      if (value && value.trim().length > 0) {
+        this.functionName = value;
+        break;
+      }
+    }
+  }
+
   /**
    * Set the namespace to be used.
    *
@@ -951,6 +959,7 @@ class Metrics extends Utility implements MetricsInterface {
       serviceName,
       singleMetric,
       defaultDimensions,
+      functionName,
     } = options;
 
     this.setEnvVarsService();
@@ -960,6 +969,7 @@ class Metrics extends Utility implements MetricsInterface {
     this.setNamespace(namespace);
     this.setService(serviceName);
     this.setDefaultDimensions(defaultDimensions);
+    this.setFunctionNameForColdStartMetric(functionName);
     this.isSingleMetric = singleMetric || false;
 
     return this;

packages/metrics/src/config/EnvironmentVariablesService.ts

@@ -11,8 +11,8 @@ class EnvironmentVariablesService
   extends CommonEnvironmentVariablesService
   implements ConfigServiceInterface
 {
-  private namespaceVariable = 'POWERTOOLS_METRICS_NAMESPACE';
-
+  private readonly namespaceVariable = 'POWERTOOLS_METRICS_NAMESPACE';
+  private readonly functionNameVariable = 'POWERTOOLS_METRICS_FUNCTION_NAME';
   private readonly disabledVariable = 'POWERTOOLS_METRICS_DISABLED';
 
   /**
@@ -22,6 +22,13 @@ class EnvironmentVariablesService
     return this.get(this.namespaceVariable);
   }
 
+  /**
+   * Get the value of the `POWERTOOLS_METRICS_FUNCTION_NAME` environment variable.
+   */
+  public getFunctionName(): string {
+    return this.get(this.functionNameVariable);
+  }
+
   /**
    * Get the value of the `POWERTOOLS_METRICS_DISABLED` or `POWERTOOLS_DEV` environment variables.
    *

packages/metrics/src/middleware/middy.ts

@@ -62,7 +62,6 @@ const logMetrics = (
 
   const logMetricsBefore = async (request: MiddyLikeRequest): Promise<void> => {
     for (const metrics of metricsInstances) {
-      metrics.setFunctionName(request.context.functionName);
       const { throwOnEmptyMetrics, defaultDimensions, captureColdStartMetric } =
         options;
       if (throwOnEmptyMetrics) {
@@ -72,7 +71,7 @@ const logMetrics = (
         metrics.setDefaultDimensions(defaultDimensions);
       }
       if (captureColdStartMetric) {
-        metrics.captureColdStartMetric();
+        metrics.captureColdStartMetric(request.context.functionName);
       }
     }
 

packages/metrics/src/types/ConfigServiceInterface.ts

@@ -12,6 +12,10 @@ interface ConfigServiceInterface extends ConfigServiceBaseInterface {
    * Get the value of the `POWERTOOLS_METRICS_NAMESPACE` environment variable.
    */
   getNamespace(): string;
+  /**
+   * Get the value of the `POWERTOOLS_METRICS_FUNCTION_NAME` environment variable.
+   */
+  getFunctionName(): string;
 }
 
 export type { ConfigServiceInterface };