Track observability business metric (metric 7) (#4420)

## Motivation and Context
Implements business metric tracking for observability providers per SEP
User Agent 2.1 specification. The metric '7' (ObservabilityOtelMetrics)
must be tracked when users configure OpenTelemetry metrics providers to
help AWS understand observability usage patterns.

## Description
This PR adds a new ObservabilityMetricDecorator that tracks the
observability metric when OpenTelemetry metrics providers are configured
through the global telemetry provider.

## Implementation
The decorator registers an ObservabilityFeatureTrackerInterceptor that
runs during request execution. It checks the global telemetry provider
and uses type downcasting to detect if an OtelMeterProvider is
configured:

- Checks global telemetry provider via
`aws_smithy_observability::global::get_telemetry_provider()`
- Uses `downcast_ref::<OtelMeterProvider>()` for reliable type detection
- Adds `as_any()` method to `ProvideMeter` trait to enable downcasting
- Stores metric in interceptor state when OTel provider is detected

When an OpenTelemetry metrics provider is configured, the metric is
tracked in the User-Agent header.

## Checklist
- [x] I have updated CHANGELOG.next.toml if I made changes to the
smithy-rs codegen or runtime crates
- [x] I have updated CHANGELOG.next.toml if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

Note: This is a draft PR for review. The implementation successfully
tracks OpenTelemetry metrics provider usage, which covers the SEP
requirements for metric 7.

---------

Co-authored-by: Landon James <[email protected]>

Author: vcjana

.changelog/observability-metrics.md

@@ -0,0 +1,9 @@
+---
+applies_to: ["client"]
+authors: ["vcjana"]
+references: []
+breaking: false
+new_feature: false
+bug_fix: false
+---
+Add support for tracking observability business metrics (OBSERVABILITY_TRACING, OBSERVABILITY_OTEL_TRACING, OBSERVABILITY_OTEL_METRICS) in User-Agent headers when telemetry providers are configured.

aws/codegen-aws-sdk/src/main/kotlin/software/amazon/smithy/rustsdk/AwsCodegenDecorator.kt

@@ -46,6 +46,7 @@ val DECORATORS: List<ClientCodegenDecorator> =
             CredentialsProviderDecorator(),
             RegionDecorator(),
             RequireEndpointRules(),
+            ObservabilityMetricDecorator(),
             EndpointOverrideMetricDecorator(),
             UserAgentDecorator(),
             SigV4AuthDecorator(),

aws/codegen-aws-sdk/src/main/kotlin/software/amazon/smithy/rustsdk/ObservabilityMetricDecorator.kt

@@ -0,0 +1,53 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.rustsdk
+
+import software.amazon.smithy.rust.codegen.client.smithy.ClientCodegenContext
+import software.amazon.smithy.rust.codegen.client.smithy.customize.ClientCodegenDecorator
+import software.amazon.smithy.rust.codegen.client.smithy.generators.ServiceRuntimePluginCustomization
+import software.amazon.smithy.rust.codegen.client.smithy.generators.ServiceRuntimePluginSection
+import software.amazon.smithy.rust.codegen.core.rustlang.CargoDependency
+import software.amazon.smithy.rust.codegen.core.rustlang.Visibility
+import software.amazon.smithy.rust.codegen.core.rustlang.rustTemplate
+import software.amazon.smithy.rust.codegen.core.rustlang.writable
+import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType
+
+/**
+ * Decorator that tracks observability business metrics when tracing/metrics providers are configured.
+ */
+class ObservabilityMetricDecorator : ClientCodegenDecorator {
+    override val name: String = "ObservabilityMetric"
+    override val order: Byte = 0
+
+    override fun serviceRuntimePluginCustomizations(
+        codegenContext: ClientCodegenContext,
+        baseCustomizations: List<ServiceRuntimePluginCustomization>,
+    ): List<ServiceRuntimePluginCustomization> =
+        baseCustomizations + listOf(ObservabilityFeatureTrackerInterceptor(codegenContext))
+}
+
+private class ObservabilityFeatureTrackerInterceptor(private val codegenContext: ClientCodegenContext) :
+    ServiceRuntimePluginCustomization() {
+    override fun section(section: ServiceRuntimePluginSection) =
+        writable {
+            if (section is ServiceRuntimePluginSection.RegisterRuntimeComponents) {
+                section.registerInterceptor(this) {
+                    val runtimeConfig = codegenContext.runtimeConfig
+                    rustTemplate(
+                        "#{Interceptor}",
+                        "Interceptor" to
+                            RuntimeType.forInlineDependency(
+                                InlineAwsDependency.forRustFile(
+                                    "observability_feature",
+                                    Visibility.PRIVATE,
+                                    CargoDependency.smithyObservability(runtimeConfig),
+                                ),
+                            ).resolve("ObservabilityFeatureTrackerInterceptor"),
+                    )
+                }
+            }
+        }
+}

aws/rust-runtime/Cargo.lock

@@ -23,6 +23,7 @@ aws-types = { path = "../aws-types" }
 aws-smithy-async = { path = "../../../rust-runtime/aws-smithy-async", features = ["rt-tokio"] }
 aws-smithy-checksums = { path = "../../../rust-runtime/aws-smithy-checksums" }
 aws-smithy-http = { path = "../../../rust-runtime/aws-smithy-http" }
+aws-smithy-observability = { path = "../../../rust-runtime/aws-smithy-observability" }
 aws-smithy-runtime = { path = "../../../rust-runtime/aws-smithy-runtime", features = ["client"] }
 aws-smithy-runtime-api = { path = "../../../rust-runtime/aws-smithy-runtime-api", features = ["client"] }
 aws-smithy-types = { path = "../../../rust-runtime/aws-smithy-types", features = ["http-body-0-4-x"] }

aws/rust-runtime/aws-inlineable/Cargo.toml

@@ -26,6 +26,10 @@
 #[allow(dead_code)]
 pub mod account_id_endpoint;
 
+/// Supporting code for tracking observability features (tracing/metrics).
+#[allow(dead_code)]
+pub mod observability_feature;
+
 /// Supporting code for the aws-chunked content encoding.
 pub mod aws_chunked;
 

aws/rust-runtime/aws-inlineable/src/lib.rs

@@ -0,0 +1,40 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+use aws_smithy_runtime::client::sdk_feature::SmithySdkFeature;
+use aws_smithy_runtime_api::{
+    box_error::BoxError,
+    client::interceptors::{context::BeforeSerializationInterceptorContextRef, Intercept},
+};
+use aws_smithy_types::config_bag::ConfigBag;
+
+// Interceptor that tracks Smithy SDK features for observability (tracing/metrics).
+#[derive(Debug, Default)]
+pub(crate) struct ObservabilityFeatureTrackerInterceptor;
+
+impl Intercept for ObservabilityFeatureTrackerInterceptor {
+    fn name(&self) -> &'static str {
+        "ObservabilityFeatureTrackerInterceptor"
+    }
+
+    fn read_before_execution(
+        &self,
+        _context: &BeforeSerializationInterceptorContextRef<'_>,
+        cfg: &mut ConfigBag,
+    ) -> Result<(), BoxError> {
+        // Check if an OpenTelemetry meter provider is configured via the global provider
+        if let Ok(telemetry_provider) = aws_smithy_observability::global::get_telemetry_provider() {
+            let meter_provider = telemetry_provider.meter_provider();
+
+            // Use provider_name() to detect OpenTelemetry without importing the otel crate.
+            if meter_provider.provider_name() == "AwsSmithyObservabilityOtelProvider" {
+                cfg.interceptor_state()
+                    .store_append(SmithySdkFeature::ObservabilityOtelMetrics);
+            }
+        }
+
+        Ok(())
+    }
+}

aws/rust-runtime/aws-inlineable/src/observability_feature.rs

@@ -1,6 +1,6 @@
 [package]
 name = "aws-runtime"
-version = "1.5.17"
+version = "1.5.18"
 authors = ["AWS Rust SDK Team <[email protected]>"]
 description = "Runtime support code for the AWS SDK. This crate isn't intended to be used directly."
 edition = "2021"

aws/rust-runtime/aws-runtime/Cargo.toml

@@ -210,6 +210,7 @@ impl ProvideBusinessMetric for SmithySdkFeature {
             FlexibleChecksumsResWhenRequired => {
                 Some(BusinessMetric::FlexibleChecksumsResWhenRequired)
             }
+            ObservabilityOtelMetrics => Some(BusinessMetric::ObservabilityOtelMetrics),
             otherwise => {
                 // This may occur if a customer upgrades only the `aws-smithy-runtime-api` crate
                 // while continuing to use an outdated version of an SDK crate or the `aws-runtime`

aws/rust-runtime/aws-runtime/src/user_agent/metrics.rs

@@ -12,6 +12,7 @@ publish = false
 
 [dev-dependencies]
 aws-config = { path = "../../build/aws-sdk/sdk/aws-config", features = ["test-util", "behavior-version-latest"] }
+aws-runtime = { path = "../../build/aws-sdk/sdk/aws-runtime", features = ["test-util"] }
 aws-sdk-dynamodb = { path = "../../build/aws-sdk/sdk/dynamodb", features = ["test-util", "behavior-version-latest"] }
 aws-sdk-s3 = { path = "../../build/aws-sdk/sdk/s3", features = ["test-util", "behavior-version-latest"] }
 aws-smithy-observability = { path = "../../build/aws-sdk/sdk/aws-smithy-observability" }