fix: pool metrics + YAML pool config (#114, #115)

src/config.rs

@@ -96,6 +96,11 @@ pub struct Config {
 
     // Cluster configuration (Issue #45)
     pub cluster: ClusterConfig,
+
+    // Connection pool overrides from YAML (Issue #114).
+    // When Some, these override env-var defaults when building the HTTP client.
+    pub pool_max_idle_per_host: Option<usize>,
+    pub pool_idle_timeout_secs: Option<u64>,
 }
 
 /// Helper to get a required environment variable.
@@ -230,6 +235,11 @@ impl Config {
         let auto_disable_percentiles_on_warning =
             env_bool("AUTO_DISABLE_PERCENTILES_ON_WARNING", true);
 
+        let (pool_max_idle_per_host, pool_idle_timeout_secs) = match &yaml_config.config.pool {
+            Some(p) => (p.max_idle_per_host, p.idle_timeout_secs),
+            None => (None, None),
+        };
+
         let config = Config {
             target_url,
             request_type,
@@ -251,6 +261,8 @@ impl Config {
             memory_critical_threshold_percent,
             auto_disable_percentiles_on_warning,
             cluster: ClusterConfig::from_env(),
+            pool_max_idle_per_host,
+            pool_idle_timeout_secs,
         };
 
         config.validate()?;
@@ -318,6 +330,11 @@ impl Config {
         let auto_disable_percentiles_on_warning =
             env_bool("AUTO_DISABLE_PERCENTILES_ON_WARNING", true);
 
+        let (pool_max_idle_per_host, pool_idle_timeout_secs) = match &yaml_config.config.pool {
+            Some(p) => (p.max_idle_per_host, p.idle_timeout_secs),
+            None => (None, None),
+        };
+
         let config = Config {
             target_url,
             request_type,
@@ -339,6 +356,8 @@ impl Config {
             memory_critical_threshold_percent,
             auto_disable_percentiles_on_warning,
             cluster: ClusterConfig::from_env(),
+            pool_max_idle_per_host,
+            pool_idle_timeout_secs,
         };
 
         config.validate()?;
@@ -504,6 +523,8 @@ impl Config {
             memory_critical_threshold_percent,
             auto_disable_percentiles_on_warning,
             cluster: ClusterConfig::from_env(),
+            pool_max_idle_per_host: None,
+            pool_idle_timeout_secs: None,
         };
 
         config.validate()?;
@@ -707,18 +728,27 @@ impl Config {
             memory_critical_threshold_percent: 90.0,
             auto_disable_percentiles_on_warning: true,
             cluster: ClusterConfig::for_testing(),
+            pool_max_idle_per_host: None,
+            pool_idle_timeout_secs: None,
         }
     }
 
     /// Creates a ClientConfig from this Config.
     pub fn to_client_config(&self) -> ClientConfig {
+        let mut pool = crate::connection_pool::PoolConfig::from_env();
+        if let Some(v) = self.pool_max_idle_per_host {
+            pool.max_idle_per_host = v;
+        }
+        if let Some(v) = self.pool_idle_timeout_secs {
+            pool.idle_timeout = Duration::from_secs(v);
+        }
         ClientConfig {
             skip_tls_verify: self.skip_tls_verify,
             resolve_target_addr: self.resolve_target_addr.clone(),
             client_cert_path: self.client_cert_path.clone(),
             client_key_path: self.client_key_path.clone(),
             custom_headers: self.custom_headers.clone(),
-            pool_config: Some(crate::connection_pool::PoolConfig::from_env()),
+            pool_config: Some(pool),
             cookie_store: false,
         }
     }

src/connection_pool.rs

@@ -8,6 +8,11 @@ use std::sync::{Arc, Mutex};
 use std::time::{Duration, Instant};
 use tracing::debug;
 
+use crate::metrics::{
+    CONNECTION_POOL_LIKELY_NEW, CONNECTION_POOL_LIKELY_REUSED, CONNECTION_POOL_REQUESTS_TOTAL,
+    CONNECTION_POOL_REUSE_RATE,
+};
+
 /// Connection pool configuration.
 #[derive(Debug, Clone)]
 pub struct PoolConfig {
@@ -212,6 +217,7 @@ impl PoolStatsTracker {
         let mut stats = self.stats.lock().unwrap();
 
         stats.total_requests += 1;
+        CONNECTION_POOL_REQUESTS_TOTAL.inc();
 
         // Track timing
         if stats.first_request.is_none() {
@@ -224,19 +230,25 @@ impl PoolStatsTracker {
         // Slow requests likely established new connections (TLS handshake adds ~50-100ms)
         if latency_ms >= self.new_connection_threshold_ms {
             stats.likely_new_connections += 1;
+            CONNECTION_POOL_LIKELY_NEW.inc();
             debug!(
                 latency_ms = latency_ms,
                 threshold = self.new_connection_threshold_ms,
                 "Request latency suggests new connection"
             );
         } else {
             stats.likely_reused_connections += 1;
+            CONNECTION_POOL_LIKELY_REUSED.inc();
             debug!(
                 latency_ms = latency_ms,
                 threshold = self.new_connection_threshold_ms,
                 "Request latency suggests reused connection"
             );
         }
+
+        // Update reuse rate gauge
+        let reuse_rate = stats.reuse_rate();
+        CONNECTION_POOL_REUSE_RATE.set(reuse_rate);
     }
 
     /// Get current connection statistics.

src/executor.rs

@@ -5,6 +5,7 @@
 //! and metrics tracking.
 
 use crate::assertions;
+use crate::connection_pool::GLOBAL_POOL_STATS;
 use crate::extractor;
 use crate::metrics::{
     CONCURRENT_SCENARIOS, SCENARIO_ASSERTIONS_TOTAL, SCENARIO_DURATION_SECONDS,
@@ -347,6 +348,7 @@ impl ScenarioExecutor {
         let response_result = request_builder.send().await;
 
         let response_time_ms = step_start.elapsed().as_millis() as u64;
+        GLOBAL_POOL_STATS.record_request(response_time_ms);
 
         match response_result {
             Ok(response) => {

src/yaml_config.rs

@@ -99,6 +99,25 @@ pub struct YamlGlobalConfig {
     /// Equivalent to the RESOLVE_TARGET_ADDR env var; env var takes precedence.
     #[serde(rename = "resolveTargetAddr")]
     pub resolve_target_addr: Option<String>,
+
+    /// Connection pool settings.  When omitted the pool uses env-var defaults
+    /// (`POOL_MAX_IDLE_PER_HOST`, `POOL_IDLE_TIMEOUT_SECS`).
+    #[serde(default)]
+    pub pool: Option<YamlPoolConfig>,
+}
+
+/// Connection pool tuning exposed via YAML.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct YamlPoolConfig {
+    /// Maximum idle connections kept per host (default: 32).
+    /// Set to 0 to force a new connection for every request.
+    #[serde(rename = "maxIdlePerHost")]
+    pub max_idle_per_host: Option<usize>,
+
+    /// Seconds an idle connection stays in the pool before cleanup (default: 30).
+    /// Set to 0 to immediately close connections after each request.
+    #[serde(rename = "idleTimeoutSecs")]
+    pub idle_timeout_secs: Option<u64>,
 }
 
 fn default_timeout() -> YamlDuration {
@@ -723,6 +742,7 @@ impl Default for YamlConfig {
                 skip_tls_verify: false,
                 custom_headers: None,
                 resolve_target_addr: None,
+                pool: None,
             },
             load: YamlLoadModel::Concurrent,
             scenarios: vec![],