Add support for POWERTOOLS_METRICS_FUNCTION_NAME.

Author: phipag

docs/core/metrics.md

@@ -111,11 +111,12 @@ Visit the AWS documentation for a complete explanation for [Amazon CloudWatch co
 
 Metrics has three global settings that will be used across all metrics emitted. Use your application or main service as the metric namespace to easily group all metrics:
 
-| Setting                        | Description                                                                     | Environment variable           | Decorator parameter |
-| ------------------------------ | ------------------------------------------------------------------------------- | ------------------------------ | ------------------- |
-| **Metric namespace**           | Logical container where all metrics will be placed e.g. `ServerlessAirline`     | `POWERTOOLS_METRICS_NAMESPACE` | `namespace`         |
-| **Service**                    | Optionally, sets **service** metric dimension across all metrics e.g. `payment` | `POWERTOOLS_SERVICE_NAME`      | `service`           |
-| **Disable Powertools Metrics** | Optionally, disables all Powertools metrics                                     | `POWERTOOLS_METRICS_DISABLED`  | N/A                 |
+| Setting                        | Description                                                                     | Environment variable               | Decorator parameter |
+| ------------------------------ | ------------------------------------------------------------------------------- | ---------------------------------- | ------------------- |
+| **Metric namespace**           | Logical container where all metrics will be placed e.g. `ServerlessAirline`     | `POWERTOOLS_METRICS_NAMESPACE`     | `namespace`         |
+| **Service**                    | Optionally, sets **service** metric dimension across all metrics e.g. `payment` | `POWERTOOLS_SERVICE_NAME`          | `service`           |
+| **Function name**              | Function name used as dimension for the cold start metric                       | `POWERTOOLS_METRICS_FUNCTION_NAME` | `functionName`      |
+| **Disable Powertools Metrics** | Optionally, disables all Powertools metrics                                     | `POWERTOOLS_METRICS_DISABLED`      | N/A                 |
 
 !!! tip "Use your application or main service as the metric namespace to easily group all metrics"
 

docs/index.md

@@ -236,10 +236,11 @@ Use the following [dependency matrix](https://github.com/eclipse-aspectj/aspectj
     **Explicit parameters take precedence over environment variables.**
 
 | Environment variable                   | Description                                                                            | Utility                   |
-|----------------------------------------|----------------------------------------------------------------------------------------|---------------------------|
+| -------------------------------------- | -------------------------------------------------------------------------------------- | ------------------------- |
 | **POWERTOOLS_SERVICE_NAME**            | Sets service name used for tracing namespace, metrics dimension and structured logging | All                       |
 | **POWERTOOLS_METRICS_NAMESPACE**       | Sets namespace used for metrics                                                        | [Metrics](./core/metrics) |
-| **POWERTOOLS_METRICS_DISABLED**       | Disables all flushing of metrics                                                        | [Metrics](./core/metrics) |
+| **POWERTOOLS_METRICS_FUNCTION_NAME**   | Function name used as dimension for the cold start metric                              | [Metrics](./core/metrics) |
+| **POWERTOOLS_METRICS_DISABLED**        | Disables all flushing of metrics                                                       | [Metrics](./core/metrics) |
 | **POWERTOOLS_LOGGER_SAMPLE_RATE**      | Debug log sampling                                                                     | [Logging](./core/logging) |
 | **POWERTOOLS_LOG_LEVEL**               | Sets logging level                                                                     | [Logging](./core/logging) |
 | **POWERTOOLS_LOGGER_LOG_EVENT**        | Enables/Disables whether to log the incoming event when using the aspect               | [Logging](./core/logging) |

powertools-metrics/src/main/java/software/amazon/lambda/powertools/metrics/internal/LambdaMetricsAspect.java

@@ -37,11 +37,18 @@ public class LambdaMetricsAspect {
     public static final String TRACE_ID_PROPERTY = "xray_trace_id";
     public static final String REQUEST_ID_PROPERTY = "function_request_id";
     private static final String SERVICE_DIMENSION = "Service";
+    private static final String FUNCTION_NAME_ENV_VAR = "POWERTOOLS_METRICS_FUNCTION_NAME";
 
     private String functionName(Metrics metrics, Context context) {
         if (!"".equals(metrics.functionName())) {
             return metrics.functionName();
         }
+
+        String envFunctionName = System.getenv(FUNCTION_NAME_ENV_VAR);
+        if (envFunctionName != null && !envFunctionName.isEmpty()) {
+            return envFunctionName;
+        }
+
         return context != null ? context.getFunctionName() : null;
     }
 

powertools-metrics/src/test/java/software/amazon/lambda/powertools/metrics/internal/LambdaMetricsAspectTest.java

@@ -162,6 +162,7 @@ void shouldCaptureColdStartMetricWhenConfigured() throws Exception {
     }
 
     @Test
+    @SetEnvironmentVariable(key = "POWERTOOLS_METRICS_FUNCTION_NAME", value = "EnvFunctionName")
     void shouldNotIncludeServiceDimensionInColdStartMetricWhenServiceUndefined() throws Exception {
         // Given - no service name set, so it will use the default undefined value
         RequestHandler<Map<String, Object>, String> handler = new HandlerWithColdStartMetricsAnnotation();
@@ -187,6 +188,7 @@ void shouldNotIncludeServiceDimensionInColdStartMetricWhenServiceUndefined() thr
 
         // FunctionName dimension should be present
         assertThat(coldStartNode.has("FunctionName")).isTrue();
+        assertThat(coldStartNode.get("FunctionName").asText()).isEqualTo("EnvFunctionName");
     }
 
     @Test