ME Pool Hardswap

src/cli.rs

@@ -196,7 +196,10 @@ use_middle_proxy = false
 log_level = "normal"
 desync_all_full = false
 update_every = 43200
-me_reinit_drain_timeout_secs = 300
+hardswap = false
+me_pool_drain_ttl_secs = 90
+me_pool_min_fresh_ratio = 0.8
+me_reinit_drain_timeout_secs = 120
 
 [network]
 ipv4 = true

src/config/defaults.rs

@@ -1,4 +1,3 @@
-use std::net::IpAddr;
 use std::collections::HashMap;
 use ipnetwork::IpNetwork;
 use serde::Deserialize;
@@ -172,11 +171,23 @@ pub(crate) fn default_proxy_config_reload_secs() -> u64 {
 }
 
 pub(crate) fn default_update_every_secs() -> u64 {
-    2 * 60 * 60
+    12 * 60 * 60
 }
 
 pub(crate) fn default_me_reinit_drain_timeout_secs() -> u64 {
-    300
+    120
+}
+
+pub(crate) fn default_me_pool_drain_ttl_secs() -> u64 {
+    90
+}
+
+pub(crate) fn default_me_pool_min_fresh_ratio() -> f32 {
+    0.8
+}
+
+pub(crate) fn default_hardswap() -> bool {
+    false
 }
 
 pub(crate) fn default_ntp_check() -> bool {

src/config/hot_reload.rs

@@ -12,6 +12,9 @@
 //! | `general` | `me_keepalive_*`              | Passed on next connection         |
 //! | `general` | `desync_all_full`             | Applied immediately               |
 //! | `general` | `update_every`                | Applied to ME updater immediately |
+//! | `general` | `hardswap`                    | Applied on next ME map update     |
+//! | `general` | `me_pool_drain_ttl_secs`      | Applied on next ME map update     |
+//! | `general` | `me_pool_min_fresh_ratio`     | Applied on next ME map update     |
 //! | `general` | `me_reinit_drain_timeout_secs`| Applied on next ME map update     |
 //! | `access`  | All user/quota fields         | Effective immediately             |
 //!
@@ -39,6 +42,9 @@ pub struct HotFields {
     pub middle_proxy_pool_size:  usize,
     pub desync_all_full:         bool,
     pub update_every_secs:       u64,
+    pub hardswap:                bool,
+    pub me_pool_drain_ttl_secs:  u64,
+    pub me_pool_min_fresh_ratio: f32,
     pub me_reinit_drain_timeout_secs: u64,
     pub me_keepalive_enabled:    bool,
     pub me_keepalive_interval_secs: u64,
@@ -55,6 +61,9 @@ impl HotFields {
             middle_proxy_pool_size:  cfg.general.middle_proxy_pool_size,
             desync_all_full:         cfg.general.desync_all_full,
             update_every_secs:       cfg.general.effective_update_every_secs(),
+            hardswap:                cfg.general.hardswap,
+            me_pool_drain_ttl_secs:  cfg.general.me_pool_drain_ttl_secs,
+            me_pool_min_fresh_ratio: cfg.general.me_pool_min_fresh_ratio,
             me_reinit_drain_timeout_secs: cfg.general.me_reinit_drain_timeout_secs,
             me_keepalive_enabled:    cfg.general.me_keepalive_enabled,
             me_keepalive_interval_secs: cfg.general.me_keepalive_interval_secs,
@@ -198,6 +207,27 @@ fn log_changes(
         );
     }
 
+    if old_hot.hardswap != new_hot.hardswap {
+        info!(
+            "config reload: hardswap: {} → {}",
+            old_hot.hardswap, new_hot.hardswap,
+        );
+    }
+
+    if old_hot.me_pool_drain_ttl_secs != new_hot.me_pool_drain_ttl_secs {
+        info!(
+            "config reload: me_pool_drain_ttl_secs: {}s → {}s",
+            old_hot.me_pool_drain_ttl_secs, new_hot.me_pool_drain_ttl_secs,
+        );
+    }
+
+    if (old_hot.me_pool_min_fresh_ratio - new_hot.me_pool_min_fresh_ratio).abs() > f32::EPSILON {
+        info!(
+            "config reload: me_pool_min_fresh_ratio: {:.3} → {:.3}",
+            old_hot.me_pool_min_fresh_ratio, new_hot.me_pool_min_fresh_ratio,
+        );
+    }
+
     if old_hot.me_reinit_drain_timeout_secs != new_hot.me_reinit_drain_timeout_secs {
         info!(
             "config reload: me_reinit_drain_timeout_secs: {}s → {}s",

src/config/load.rs

@@ -145,6 +145,24 @@ impl ProxyConfig {
             }
         }
 
+        if !(0.0..=1.0).contains(&config.general.me_pool_min_fresh_ratio) {
+            return Err(ProxyError::Config(
+                "general.me_pool_min_fresh_ratio must be within [0.0, 1.0]".to_string(),
+            ));
+        }
+
+        if config.general.effective_me_pool_force_close_secs() > 0
+            && config.general.effective_me_pool_force_close_secs()
+                < config.general.me_pool_drain_ttl_secs
+        {
+            warn!(
+                me_pool_drain_ttl_secs = config.general.me_pool_drain_ttl_secs,
+                me_reinit_drain_timeout_secs = config.general.effective_me_pool_force_close_secs(),
+                "force-close timeout is lower than drain TTL; bumping force-close timeout to TTL"
+            );
+            config.general.me_reinit_drain_timeout_secs = config.general.me_pool_drain_ttl_secs;
+        }
+
         // Validate secrets.
         for (user, secret) in &config.access.users {
             if !secret.chars().all(|c| c.is_ascii_hexdigit()) || secret.len() != 32 {
@@ -439,4 +457,45 @@ mod tests {
         assert!(err.contains("general.update_every must be > 0"));
         let _ = std::fs::remove_file(path);
     }
+
+    #[test]
+    fn me_pool_min_fresh_ratio_out_of_range_is_rejected() {
+        let toml = r#"
+            [general]
+            me_pool_min_fresh_ratio = 1.5
+
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+        "#;
+        let dir = std::env::temp_dir();
+        let path = dir.join("telemt_me_pool_min_ratio_invalid_test.toml");
+        std::fs::write(&path, toml).unwrap();
+        let err = ProxyConfig::load(&path).unwrap_err().to_string();
+        assert!(err.contains("general.me_pool_min_fresh_ratio must be within [0.0, 1.0]"));
+        let _ = std::fs::remove_file(path);
+    }
+
+    #[test]
+    fn force_close_bumped_when_below_drain_ttl() {
+        let toml = r#"
+            [general]
+            me_pool_drain_ttl_secs = 90
+            me_reinit_drain_timeout_secs = 30
+
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+        "#;
+        let dir = std::env::temp_dir();
+        let path = dir.join("telemt_force_close_bump_test.toml");
+        std::fs::write(&path, toml).unwrap();
+        let cfg = ProxyConfig::load(&path).unwrap();
+        assert_eq!(cfg.general.me_reinit_drain_timeout_secs, 90);
+        let _ = std::fs::remove_file(path);
+    }
 }

src/config/types.rs

@@ -206,6 +206,11 @@ pub struct GeneralConfig {
     #[serde(default = "default_desync_all_full")]
     pub desync_all_full: bool,
 
+    /// Enable C-like hard-swap for ME pool generations.
+    /// When true, Telemt prewarms a new generation and switches once full coverage is reached.
+    #[serde(default = "default_hardswap")]
+    pub hardswap: bool,
+
     /// Enable staggered warmup of extra ME writers.
     #[serde(default = "default_true")]
     pub me_warmup_stagger_enabled: bool,
@@ -262,6 +267,16 @@ pub struct GeneralConfig {
     #[serde(default)]
     pub update_every: Option<u64>,
 
+    /// Drain-TTL in seconds for stale ME writers after endpoint map changes.
+    /// During TTL, stale writers may be used only as fallback for new bindings.
+    #[serde(default = "default_me_pool_drain_ttl_secs")]
+    pub me_pool_drain_ttl_secs: u64,
+
+    /// Minimum desired-DC coverage ratio required before draining stale writers.
+    /// Range: 0.0..=1.0.
+    #[serde(default = "default_me_pool_min_fresh_ratio")]
+    pub me_pool_min_fresh_ratio: f32,
+
     /// Drain timeout in seconds for stale ME writers after endpoint map changes.
     /// Set to 0 to keep stale writers draining indefinitely (no force-close).
     #[serde(default = "default_me_reinit_drain_timeout_secs")]
@@ -328,8 +343,11 @@ impl Default for GeneralConfig {
             crypto_pending_buffer: default_crypto_pending_buffer(),
             max_client_frame: default_max_client_frame(),
             desync_all_full: default_desync_all_full(),
+            hardswap: default_hardswap(),
             fast_mode_min_tls_record: default_fast_mode_min_tls_record(),
             update_every: Some(default_update_every_secs()),
+            me_pool_drain_ttl_secs: default_me_pool_drain_ttl_secs(),
+            me_pool_min_fresh_ratio: default_me_pool_min_fresh_ratio(),
             me_reinit_drain_timeout_secs: default_me_reinit_drain_timeout_secs(),
             proxy_secret_auto_reload_secs: default_proxy_secret_reload_secs(),
             proxy_config_auto_reload_secs: default_proxy_config_reload_secs(),
@@ -348,6 +366,12 @@ impl GeneralConfig {
         self.update_every
             .unwrap_or_else(|| self.proxy_secret_auto_reload_secs.min(self.proxy_config_auto_reload_secs))
     }
+
+    /// Resolve force-close timeout for stale writers.
+    /// `me_reinit_drain_timeout_secs` remains backward-compatible alias.
+    pub fn effective_me_pool_force_close_secs(&self) -> u64 {
+        self.me_reinit_drain_timeout_secs
+    }
 }
 
 /// `[general.links]` — proxy link generation settings.

src/main.rs

@@ -73,36 +73,27 @@ fn parse_cli() -> (String, bool, Option<String>) {
                 log_level = Some(s.trim_start_matches("--log-level=").to_string());
             }
             "--help" | "-h" => {
-                eprintln!("telemt - Telegram MTProto Proxy v{}", env!("CARGO_PKG_VERSION"));
+                eprintln!("Usage: telemt [config.toml] [OPTIONS]");
                 eprintln!();
-                eprintln!("USAGE:");
+                eprintln!("Options:");
-                eprintln!("    telemt [CONFIG] [OPTIONS]");
+                eprintln!("  --silent, -s            Suppress info logs");
-                eprintln!("    telemt --init [INIT_OPTIONS]");
+                eprintln!("  --log-level <LEVEL>     debug|verbose|normal|silent");
+                eprintln!("  --help, -h              Show this help");
                 eprintln!();
-                eprintln!("ARGS:");
+                eprintln!("Setup (fire-and-forget):");
-                eprintln!("    <CONFIG>       Path to config file (default: config.toml)");
+                eprintln!(
-                eprintln!();
+                    "  --init                  Generate config, install systemd service, start"
-                eprintln!("OPTIONS:");
+                );
-                eprintln!("    -s, --silent           Suppress info logs (equivalent to --log-level silent)");
-                eprintln!("    --log-level <LEVEL>    Set log level [possible values: debug, verbose, normal, silent]");
-                eprintln!("    -h, --help             Show this help message");
-                eprintln!("    -V, --version          Print version number");
-                eprintln!();
-                eprintln!("INIT OPTIONS (fire-and-forget setup):");
-                eprintln!("    --init                 Generate config, install systemd service, and start");
                 eprintln!("    --port <PORT>          Listen port (default: 443)");
-                eprintln!("    --domain <DOMAIN>      TLS domain for masking (default: www.google.com)");
+                eprintln!(
-                eprintln!("    --secret <HEX>         32-char hex secret (auto-generated if omitted)");
+                    "    --domain <DOMAIN>      TLS domain for masking (default: www.google.com)"
-                eprintln!("    --user <NAME>          Username for proxy access (default: user)");
+                );
+                eprintln!(
+                    "    --secret <HEX>         32-char hex secret (auto-generated if omitted)"
+                );
+                eprintln!("    --user <NAME>          Username (default: user)");
                 eprintln!("    --config-dir <DIR>     Config directory (default: /etc/telemt)");
-                eprintln!("    --no-start             Create config and service but don't start");
+                eprintln!("    --no-start             Don't start the service after install");
-                eprintln!();
-                eprintln!("EXAMPLES:");
-                eprintln!("    telemt                           # Run with default config");
-                eprintln!("    telemt /etc/telemt/config.toml   # Run with specific config");
-                eprintln!("    telemt --log-level debug         # Run with debug logging");
-                eprintln!("    telemt --init                    # Quick setup with defaults");
-                eprintln!("    telemt --init --port 8443 --user admin  # Custom setup");
                 std::process::exit(0);
             }
             "--version" | "-V" => {
@@ -371,6 +362,10 @@ match crate::transport::middle_proxy::fetch_proxy_secret(proxy_secret_path).awai
                     config.general.me_reconnect_backoff_base_ms,
                     config.general.me_reconnect_backoff_cap_ms,
                     config.general.me_reconnect_fast_retry_count,
+                    config.general.hardswap,
+                    config.general.me_pool_drain_ttl_secs,
+                    config.general.effective_me_pool_force_close_secs(),
+                    config.general.me_pool_min_fresh_ratio,
                 );
 
                 let pool_size = config.general.middle_proxy_pool_size.max(1);

src/metrics.rs

@@ -175,6 +175,30 @@ fn render_metrics(stats: &Stats) -> String {
         stats.get_desync_frames_bucket_gt_10()
     );
 
+    let _ = writeln!(out, "# HELP telemt_pool_swap_total Successful ME pool swaps");
+    let _ = writeln!(out, "# TYPE telemt_pool_swap_total counter");
+    let _ = writeln!(out, "telemt_pool_swap_total {}", stats.get_pool_swap_total());
+
+    let _ = writeln!(out, "# HELP telemt_pool_drain_active Active draining ME writers");
+    let _ = writeln!(out, "# TYPE telemt_pool_drain_active gauge");
+    let _ = writeln!(out, "telemt_pool_drain_active {}", stats.get_pool_drain_active());
+
+    let _ = writeln!(out, "# HELP telemt_pool_force_close_total Forced close events for draining writers");
+    let _ = writeln!(out, "# TYPE telemt_pool_force_close_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_pool_force_close_total {}",
+        stats.get_pool_force_close_total()
+    );
+
+    let _ = writeln!(out, "# HELP telemt_pool_stale_pick_total Stale writer fallback picks for new binds");
+    let _ = writeln!(out, "# TYPE telemt_pool_stale_pick_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_pool_stale_pick_total {}",
+        stats.get_pool_stale_pick_total()
+    );
+
     let _ = writeln!(out, "# HELP telemt_user_connections_total Per-user total connections");
     let _ = writeln!(out, "# TYPE telemt_user_connections_total counter");
     let _ = writeln!(out, "# HELP telemt_user_connections_current Per-user active connections");

src/proxy/middle_relay.rs

@@ -184,6 +184,7 @@ where
     let user = success.user.clone();
     let peer = success.peer;
     let proto_tag = success.proto_tag;
+    let pool_generation = me_pool.current_generation();
 
     info!(
         user = %user,
@@ -191,6 +192,7 @@ where
         dc = success.dc_idx,
         proto = ?proto_tag,
         mode = "middle_proxy",
+        pool_generation,
         "Routing via Middle-End"
     );
 
@@ -220,6 +222,7 @@ where
         peer_hash = format_args!("0x{:016x}", forensics.peer_hash),
         desync_all_full = forensics.desync_all_full,
         proto_flags = format_args!("0x{:08x}", proto_flags),
+        pool_generation,
         "ME relay started"
     );
 

src/stats/mod.rs

@@ -38,6 +38,10 @@ pub struct Stats {
     desync_frames_bucket_1_2: AtomicU64,
     desync_frames_bucket_3_10: AtomicU64,
     desync_frames_bucket_gt_10: AtomicU64,
+    pool_swap_total: AtomicU64,
+    pool_drain_active: AtomicU64,
+    pool_force_close_total: AtomicU64,
+    pool_stale_pick_total: AtomicU64,
     user_stats: DashMap<String, UserStats>,
     start_time: parking_lot::RwLock<Option<Instant>>,
 }
@@ -108,6 +112,35 @@ impl Stats {
             }
         }
     }
+    pub fn increment_pool_swap_total(&self) {
+        self.pool_swap_total.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_pool_drain_active(&self) {
+        self.pool_drain_active.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn decrement_pool_drain_active(&self) {
+        let mut current = self.pool_drain_active.load(Ordering::Relaxed);
+        loop {
+            if current == 0 {
+                break;
+            }
+            match self.pool_drain_active.compare_exchange_weak(
+                current,
+                current - 1,
+                Ordering::Relaxed,
+                Ordering::Relaxed,
+            ) {
+                Ok(_) => break,
+                Err(actual) => current = actual,
+            }
+        }
+    }
+    pub fn increment_pool_force_close_total(&self) {
+        self.pool_force_close_total.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_pool_stale_pick_total(&self) {
+        self.pool_stale_pick_total.fetch_add(1, Ordering::Relaxed);
+    }
     pub fn get_connects_all(&self) -> u64 { self.connects_all.load(Ordering::Relaxed) }
     pub fn get_connects_bad(&self) -> u64 { self.connects_bad.load(Ordering::Relaxed) }
     pub fn get_me_keepalive_sent(&self) -> u64 { self.me_keepalive_sent.load(Ordering::Relaxed) }
@@ -149,6 +182,18 @@ impl Stats {
     pub fn get_desync_frames_bucket_gt_10(&self) -> u64 {
         self.desync_frames_bucket_gt_10.load(Ordering::Relaxed)
     }
+    pub fn get_pool_swap_total(&self) -> u64 {
+        self.pool_swap_total.load(Ordering::Relaxed)
+    }
+    pub fn get_pool_drain_active(&self) -> u64 {
+        self.pool_drain_active.load(Ordering::Relaxed)
+    }
+    pub fn get_pool_force_close_total(&self) -> u64 {
+        self.pool_force_close_total.load(Ordering::Relaxed)
+    }
+    pub fn get_pool_stale_pick_total(&self) -> u64 {
+        self.pool_stale_pick_total.load(Ordering::Relaxed)
+    }
     
     pub fn increment_user_connects(&self, user: &str) {
         self.user_stats.entry(user.to_string()).or_default()

src/transport/middle_proxy/config_updater.rs

@@ -131,6 +131,13 @@ pub async fn fetch_proxy_config(url: &str) -> Result<ProxyConfigData> {
 }
 
 async fn run_update_cycle(pool: &Arc<MePool>, rng: &Arc<SecureRandom>, cfg: &ProxyConfig) {
+    pool.update_runtime_reinit_policy(
+        cfg.general.hardswap,
+        cfg.general.me_pool_drain_ttl_secs,
+        cfg.general.effective_me_pool_force_close_secs(),
+        cfg.general.me_pool_min_fresh_ratio,
+    );
+
     let mut maps_changed = false;
 
     // Update proxy config v4
@@ -162,12 +169,7 @@ async fn run_update_cycle(pool: &Arc<MePool>, rng: &Arc<SecureRandom>, cfg: &Pro
     }
 
     if maps_changed {
-        let drain_timeout = if cfg.general.me_reinit_drain_timeout_secs == 0 {
+        pool.zero_downtime_reinit_after_map_change(rng.as_ref())
-            None
-        } else {
-            Some(Duration::from_secs(cfg.general.me_reinit_drain_timeout_secs))
-        };
-        pool.zero_downtime_reinit_after_map_change(rng.as_ref(), drain_timeout)
             .await;
     }
 
@@ -224,6 +226,12 @@ pub async fn me_config_updater(
                     break;
                 }
                 let cfg = config_rx.borrow().clone();
+                pool.update_runtime_reinit_policy(
+                    cfg.general.hardswap,
+                    cfg.general.me_pool_drain_ttl_secs,
+                    cfg.general.effective_me_pool_force_close_secs(),
+                    cfg.general.me_pool_min_fresh_ratio,
+                );
                 let new_secs = cfg.general.effective_update_every_secs().max(1);
                 if new_secs == update_every_secs {
                     continue;

src/transport/middle_proxy/health.rs

@@ -68,6 +68,7 @@ async fn check_family(
         .read()
         .await
         .iter()
+        .filter(|w| !w.draining.load(std::sync::atomic::Ordering::Relaxed))
         .map(|w| w.addr)
         .collect();
 

src/transport/middle_proxy/pool.rs

@@ -1,14 +1,14 @@
 use std::collections::{HashMap, HashSet};
 use std::net::{IpAddr, Ipv6Addr, SocketAddr};
 use std::sync::Arc;
-use std::sync::atomic::{AtomicBool, AtomicI32, AtomicU64, AtomicUsize, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicI32, AtomicU32, AtomicU64, AtomicUsize, Ordering};
 use bytes::BytesMut;
 use rand::Rng;
 use rand::seq::SliceRandom;
 use tokio::sync::{Mutex, RwLock, mpsc, Notify};
 use tokio_util::sync::CancellationToken;
 use tracing::{debug, info, warn};
-use std::time::{Duration, Instant};
+use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
 
 use crate::crypto::SecureRandom;
 use crate::error::{ProxyError, Result};
@@ -27,10 +27,13 @@ const ME_ACTIVE_PING_JITTER_SECS: i64 = 5;
 pub struct MeWriter {
     pub id: u64,
     pub addr: SocketAddr,
+    pub generation: u64,
     pub tx: mpsc::Sender<WriterCommand>,
     pub cancel: CancellationToken,
     pub degraded: Arc<AtomicBool>,
     pub draining: Arc<AtomicBool>,
+    pub draining_started_at_epoch_secs: Arc<AtomicU64>,
+    pub allow_drain_fallback: Arc<AtomicBool>,
 }
 
 pub struct MePool {
@@ -73,6 +76,11 @@ pub struct MePool {
     pub(super) writer_available: Arc<Notify>,
     pub(super) conn_count: AtomicUsize,
     pub(super) stats: Arc<crate::stats::Stats>,
+    pub(super) generation: AtomicU64,
+    pub(super) hardswap: AtomicBool,
+    pub(super) me_pool_drain_ttl_secs: AtomicU64,
+    pub(super) me_pool_force_close_secs: AtomicU64,
+    pub(super) me_pool_min_fresh_ratio_permille: AtomicU32,
     pool_size: usize,
 }
 
@@ -83,6 +91,22 @@ pub struct NatReflectionCache {
 }
 
 impl MePool {
+    fn ratio_to_permille(ratio: f32) -> u32 {
+        let clamped = ratio.clamp(0.0, 1.0);
+        (clamped * 1000.0).round() as u32
+    }
+
+    fn permille_to_ratio(permille: u32) -> f32 {
+        (permille.min(1000) as f32) / 1000.0
+    }
+
+    fn now_epoch_secs() -> u64 {
+        SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs()
+    }
+
     pub fn new(
         proxy_tag: Option<Vec<u8>>,
         proxy_secret: Vec<u8>,
@@ -110,6 +134,10 @@ impl MePool {
         me_reconnect_backoff_base_ms: u64,
         me_reconnect_backoff_cap_ms: u64,
         me_reconnect_fast_retry_count: u32,
+        hardswap: bool,
+        me_pool_drain_ttl_secs: u64,
+        me_pool_force_close_secs: u64,
+        me_pool_min_fresh_ratio: f32,
     ) -> Arc<Self> {
         Arc::new(Self {
             registry: Arc::new(ConnRegistry::new()),
@@ -152,6 +180,11 @@ impl MePool {
             nat_reflection_cache: Arc::new(Mutex::new(NatReflectionCache::default())),
             writer_available: Arc::new(Notify::new()),
             conn_count: AtomicUsize::new(0),
+            generation: AtomicU64::new(1),
+            hardswap: AtomicBool::new(hardswap),
+            me_pool_drain_ttl_secs: AtomicU64::new(me_pool_drain_ttl_secs),
+            me_pool_force_close_secs: AtomicU64::new(me_pool_force_close_secs),
+            me_pool_min_fresh_ratio_permille: AtomicU32::new(Self::ratio_to_permille(me_pool_min_fresh_ratio)),
         })
     }
 
@@ -159,6 +192,25 @@ impl MePool {
         self.proxy_tag.is_some()
     }
 
+    pub fn current_generation(&self) -> u64 {
+        self.generation.load(Ordering::Relaxed)
+    }
+
+    pub fn update_runtime_reinit_policy(
+        &self,
+        hardswap: bool,
+        drain_ttl_secs: u64,
+        force_close_secs: u64,
+        min_fresh_ratio: f32,
+    ) {
+        self.hardswap.store(hardswap, Ordering::Relaxed);
+        self.me_pool_drain_ttl_secs.store(drain_ttl_secs, Ordering::Relaxed);
+        self.me_pool_force_close_secs
+            .store(force_close_secs, Ordering::Relaxed);
+        self.me_pool_min_fresh_ratio_permille
+            .store(Self::ratio_to_permille(min_fresh_ratio), Ordering::Relaxed);
+    }
+
     pub fn reset_stun_state(&self) {
         self.nat_probe_attempts.store(0, Ordering::Relaxed);
         self.nat_probe_disabled.store(false, Ordering::Relaxed);
@@ -177,6 +229,42 @@ impl MePool {
         self.writers.clone()
     }
 
+    fn force_close_timeout(&self) -> Option<Duration> {
+        let secs = self.me_pool_force_close_secs.load(Ordering::Relaxed);
+        if secs == 0 {
+            None
+        } else {
+            Some(Duration::from_secs(secs))
+        }
+    }
+
+    fn coverage_ratio(
+        desired_by_dc: &HashMap<i32, HashSet<SocketAddr>>,
+        active_writer_addrs: &HashSet<SocketAddr>,
+    ) -> (f32, Vec<i32>) {
+        if desired_by_dc.is_empty() {
+            return (1.0, Vec::new());
+        }
+
+        let mut missing_dc = Vec::<i32>::new();
+        let mut covered = 0usize;
+        for (dc, endpoints) in desired_by_dc {
+            if endpoints.is_empty() {
+                continue;
+            }
+            if endpoints.iter().any(|addr| active_writer_addrs.contains(addr)) {
+                covered += 1;
+            } else {
+                missing_dc.push(*dc);
+            }
+        }
+
+        missing_dc.sort_unstable();
+        let total = desired_by_dc.len().max(1);
+        let ratio = (covered as f32) / (total as f32);
+        (ratio, missing_dc)
+    }
+
     pub async fn reconcile_connections(self: &Arc<Self>, rng: &SecureRandom) {
         let writers = self.writers.read().await;
         let current: HashSet<SocketAddr> = writers
@@ -235,39 +323,104 @@ impl MePool {
         out
     }
 
+    async fn warmup_generation_for_all_dcs(
+        self: &Arc<Self>,
+        rng: &SecureRandom,
+        generation: u64,
+        desired_by_dc: &HashMap<i32, HashSet<SocketAddr>>,
+    ) {
+        for endpoints in desired_by_dc.values() {
+            if endpoints.is_empty() {
+                continue;
+            }
+
+            let has_fresh = {
+                let ws = self.writers.read().await;
+                ws.iter().any(|w| {
+                    !w.draining.load(Ordering::Relaxed)
+                        && w.generation == generation
+                        && endpoints.contains(&w.addr)
+                })
+            };
+
+            if has_fresh {
+                continue;
+            }
+
+            let mut shuffled: Vec<SocketAddr> = endpoints.iter().copied().collect();
+            shuffled.shuffle(&mut rand::rng());
+            for addr in shuffled {
+                if self.connect_one(addr, rng).await.is_ok() {
+                    break;
+                }
+            }
+        }
+    }
+
     pub async fn zero_downtime_reinit_after_map_change(
         self: &Arc<Self>,
         rng: &SecureRandom,
-        drain_timeout: Option<Duration>,
     ) {
-        // Stage 1: prewarm writers for new endpoint maps before draining old ones.
-        self.reconcile_connections(rng).await;
-
         let desired_by_dc = self.desired_dc_endpoints().await;
         if desired_by_dc.is_empty() {
             warn!("ME endpoint map is empty after update; skipping stale writer drain");
             return;
         }
 
+        let previous_generation = self.current_generation();
+        let generation = self.generation.fetch_add(1, Ordering::Relaxed) + 1;
+        let hardswap = self.hardswap.load(Ordering::Relaxed);
+
+        if hardswap {
+            self.warmup_generation_for_all_dcs(rng, generation, &desired_by_dc)
+                .await;
+        } else {
+            self.reconcile_connections(rng).await;
+        }
+
         let writers = self.writers.read().await;
         let active_writer_addrs: HashSet<SocketAddr> = writers
             .iter()
             .filter(|w| !w.draining.load(Ordering::Relaxed))
             .map(|w| w.addr)
             .collect();
-
+        let min_ratio = Self::permille_to_ratio(
-        let mut missing_dc = Vec::<i32>::new();
+            self.me_pool_min_fresh_ratio_permille
-        for (dc, endpoints) in &desired_by_dc {
+                .load(Ordering::Relaxed),
-            if endpoints.is_empty() {
+        );
-                continue;
+        let (coverage_ratio, missing_dc) = Self::coverage_ratio(&desired_by_dc, &active_writer_addrs);
-            }
+        if !hardswap && coverage_ratio < min_ratio {
-            if !endpoints.iter().any(|addr| active_writer_addrs.contains(addr)) {
+            warn!(
-                missing_dc.push(*dc);
+                previous_generation,
-            }
+                generation,
+                coverage_ratio = format_args!("{coverage_ratio:.3}"),
+                min_ratio = format_args!("{min_ratio:.3}"),
+                missing_dc = ?missing_dc,
+                "ME reinit coverage below threshold; keeping stale writers"
+            );
+            return;
         }
 
-        if !missing_dc.is_empty() {
+        if hardswap {
-            missing_dc.sort_unstable();
+            let fresh_writer_addrs: HashSet<SocketAddr> = writers
+                .iter()
+                .filter(|w| !w.draining.load(Ordering::Relaxed))
+                .filter(|w| w.generation == generation)
+                .map(|w| w.addr)
+                .collect();
+            let (fresh_ratio, fresh_missing_dc) =
+                Self::coverage_ratio(&desired_by_dc, &fresh_writer_addrs);
+            if !fresh_missing_dc.is_empty() {
+                warn!(
+                    previous_generation,
+                    generation,
+                    fresh_ratio = format_args!("{fresh_ratio:.3}"),
+                    missing_dc = ?fresh_missing_dc,
+                    "ME hardswap pending: fresh generation coverage incomplete"
+                );
+                return;
+            }
+        } else if !missing_dc.is_empty() {
             warn!(
                 missing_dc = ?missing_dc,
                 // Keep stale writers alive when fresh coverage is incomplete.
@@ -284,7 +437,13 @@ impl MePool {
         let stale_writer_ids: Vec<u64> = writers
             .iter()
             .filter(|w| !w.draining.load(Ordering::Relaxed))
-            .filter(|w| !desired_addrs.contains(&w.addr))
+            .filter(|w| {
+                if hardswap {
+                    w.generation < generation
+                } else {
+                    !desired_addrs.contains(&w.addr)
+                }
+            })
             .map(|w| w.id)
             .collect();
         drop(writers);
@@ -294,14 +453,21 @@ impl MePool {
             return;
         }
 
+        let drain_timeout = self.force_close_timeout();
         let drain_timeout_secs = drain_timeout.map(|d| d.as_secs()).unwrap_or(0);
         info!(
             stale_writers = stale_writer_ids.len(),
+            previous_generation,
+            generation,
+            hardswap,
+            coverage_ratio = format_args!("{coverage_ratio:.3}"),
+            min_ratio = format_args!("{min_ratio:.3}"),
             drain_timeout_secs,
             "ME map update covered; draining stale writers"
         );
+        self.stats.increment_pool_swap_total();
         for writer_id in stale_writer_ids {
-            self.mark_writer_draining_with_timeout(writer_id, drain_timeout)
+            self.mark_writer_draining_with_timeout(writer_id, drain_timeout, !hardswap)
                 .await;
         }
     }
@@ -507,9 +673,12 @@ impl MePool {
         let hs = self.handshake_only(stream, addr, rng).await?;
 
         let writer_id = self.next_writer_id.fetch_add(1, Ordering::Relaxed);
+        let generation = self.current_generation();
         let cancel = CancellationToken::new();
         let degraded = Arc::new(AtomicBool::new(false));
         let draining = Arc::new(AtomicBool::new(false));
+        let draining_started_at_epoch_secs = Arc::new(AtomicU64::new(0));
+        let allow_drain_fallback = Arc::new(AtomicBool::new(false));
         let (tx, mut rx) = mpsc::channel::<WriterCommand>(4096);
         let mut rpc_writer = RpcWriter {
             writer: hs.wr,
@@ -540,10 +709,13 @@ impl MePool {
         let writer = MeWriter {
             id: writer_id,
             addr,
+            generation,
             tx: tx.clone(),
             cancel: cancel.clone(),
             degraded: degraded.clone(),
             draining: draining.clone(),
+            draining_started_at_epoch_secs: draining_started_at_epoch_secs.clone(),
+            allow_drain_fallback: allow_drain_fallback.clone(),
         };
         self.writers.write().await.push(writer.clone());
         self.conn_count.fetch_add(1, Ordering::Relaxed);
@@ -715,6 +887,9 @@ impl MePool {
             let mut ws = self.writers.write().await;
             if let Some(pos) = ws.iter().position(|w| w.id == writer_id) {
                 let w = ws.remove(pos);
+                if w.draining.load(Ordering::Relaxed) {
+                    self.stats.decrement_pool_drain_active();
+                }
                 w.cancel.cancel();
                 close_tx = Some(w.tx.clone());
                 self.conn_count.fetch_sub(1, Ordering::Relaxed);
@@ -731,11 +906,20 @@ impl MePool {
         self: &Arc<Self>,
         writer_id: u64,
         timeout: Option<Duration>,
+        allow_drain_fallback: bool,
     ) {
         let timeout = timeout.filter(|d| !d.is_zero());
         let found = {
             let mut ws = self.writers.write().await;
             if let Some(w) = ws.iter_mut().find(|w| w.id == writer_id) {
+                let already_draining = w.draining.swap(true, Ordering::Relaxed);
+                w.allow_drain_fallback
+                    .store(allow_drain_fallback, Ordering::Relaxed);
+                w.draining_started_at_epoch_secs
+                    .store(Self::now_epoch_secs(), Ordering::Relaxed);
+                if !already_draining {
+                    self.stats.increment_pool_drain_active();
+                }
                 w.draining.store(true, Ordering::Relaxed);
                 true
             } else {
@@ -748,7 +932,12 @@ impl MePool {
         }
 
         let timeout_secs = timeout.map(|d| d.as_secs()).unwrap_or(0);
-        debug!(writer_id, timeout_secs, "ME writer marked draining");
+        debug!(
+            writer_id,
+            timeout_secs,
+            allow_drain_fallback,
+            "ME writer marked draining"
+        );
 
         let pool = Arc::downgrade(self);
         tokio::spawn(async move {
@@ -758,6 +947,7 @@ impl MePool {
                     if let Some(deadline_at) = deadline {
                         if Instant::now() >= deadline_at {
                             warn!(writer_id, "Drain timeout, force-closing");
+                            p.stats.increment_pool_force_close_total();
                             let _ = p.remove_writer_and_close_clients(writer_id).await;
                             break;
                         }
@@ -775,10 +965,31 @@ impl MePool {
     }
 
     pub(crate) async fn mark_writer_draining(self: &Arc<Self>, writer_id: u64) {
-        self.mark_writer_draining_with_timeout(writer_id, Some(Duration::from_secs(300)))
+        self.mark_writer_draining_with_timeout(writer_id, Some(Duration::from_secs(300)), false)
             .await;
     }
 
+    pub(super) fn writer_accepts_new_binding(&self, writer: &MeWriter) -> bool {
+        if !writer.draining.load(Ordering::Relaxed) {
+            return true;
+        }
+        if !writer.allow_drain_fallback.load(Ordering::Relaxed) {
+            return false;
+        }
+
+        let ttl_secs = self.me_pool_drain_ttl_secs.load(Ordering::Relaxed);
+        if ttl_secs == 0 {
+            return true;
+        }
+
+        let started = writer.draining_started_at_epoch_secs.load(Ordering::Relaxed);
+        if started == 0 {
+            return false;
+        }
+
+        Self::now_epoch_secs().saturating_sub(started) <= ttl_secs
+    }
+
 }
 
 fn hex_dump(data: &[u8]) -> String {

src/transport/middle_proxy/send.rs

@@ -134,8 +134,8 @@ impl MePool {
             candidate_indices.sort_by_key(|idx| {
                 let w = &writers_snapshot[*idx];
                 let degraded = w.degraded.load(Ordering::Relaxed);
-                let draining = w.draining.load(Ordering::Relaxed);
+                let stale = (w.generation < self.current_generation()) as usize;
-                (draining as usize, degraded as usize)
+                (stale, degraded as usize)
             });
 
             let start = self.rr.fetch_add(1, Ordering::Relaxed) as usize % candidate_indices.len();
@@ -143,13 +143,23 @@ impl MePool {
             for offset in 0..candidate_indices.len() {
                 let idx = candidate_indices[(start + offset) % candidate_indices.len()];
                 let w = &writers_snapshot[idx];
-                if w.draining.load(Ordering::Relaxed) {
+                if !self.writer_accepts_new_binding(w) {
                     continue;
                 }
                 if w.tx.send(WriterCommand::Data(payload.clone())).await.is_ok() {
                     self.registry
                         .bind_writer(conn_id, w.id, w.tx.clone(), meta.clone())
                         .await;
+                    if w.generation < self.current_generation() {
+                        self.stats.increment_pool_stale_pick_total();
+                        debug!(
+                            conn_id,
+                            writer_id = w.id,
+                            writer_generation = w.generation,
+                            current_generation = self.current_generation(),
+                            "Selected stale ME writer for fallback bind"
+                        );
+                    }
                     return Ok(());
                 } else {
                     warn!(writer_id = w.id, "ME writer channel closed");
@@ -159,7 +169,7 @@ impl MePool {
             }
 
             let w = writers_snapshot[candidate_indices[start]].clone();
-            if w.draining.load(Ordering::Relaxed) {
+            if !self.writer_accepts_new_binding(&w) {
                 continue;
             }
             match w.tx.send(WriterCommand::Data(payload.clone())).await {
@@ -167,6 +177,9 @@ impl MePool {
                     self.registry
                         .bind_writer(conn_id, w.id, w.tx.clone(), meta.clone())
                         .await;
+                    if w.generation < self.current_generation() {
+                        self.stats.increment_pool_stale_pick_total();
+                    }
                     return Ok(());
                 }
                 Err(_) => {
@@ -245,13 +258,13 @@ impl MePool {
 
         if preferred.is_empty() {
             return (0..writers.len())
-                .filter(|i| !writers[*i].draining.load(Ordering::Relaxed))
+                .filter(|i| self.writer_accepts_new_binding(&writers[*i]))
                 .collect();
         }
 
         let mut out = Vec::new();
         for (idx, w) in writers.iter().enumerate() {
-            if w.draining.load(Ordering::Relaxed) {
+            if !self.writer_accepts_new_binding(w) {
                 continue;
             }
             if preferred.iter().any(|p| *p == w.addr) {
@@ -260,7 +273,7 @@ impl MePool {
         }
         if out.is_empty() {
             return (0..writers.len())
-                .filter(|i| !writers[*i].draining.load(Ordering::Relaxed))
+                .filter(|i| self.writer_accepts_new_binding(&writers[*i]))
                 .collect();
         }
         out