Support min load besides random routing key assignment policy in ManualPolicy (#16767)

sgl-model-gateway/bindings/python/src/lib.rs

@@ -348,6 +348,7 @@ struct Router {
     eviction_interval_secs: u64,
     max_tree_size: usize,
     max_idle_secs: u64,
+    assignment_mode: String,
     max_payload_size: usize,
     dp_aware: bool,
     api_key: Option<String>,
@@ -457,6 +458,11 @@ impl Router {
                 PolicyType::Manual => ConfigPolicyConfig::Manual {
                     eviction_interval_secs: self.eviction_interval_secs,
                     max_idle_secs: self.max_idle_secs,
+                    assignment_mode: match self.assignment_mode.as_str() {
+                        "random" => config::ManualAssignmentMode::Random,
+                        "min_load" => config::ManualAssignmentMode::MinLoad,
+                        other => panic!("Unknown assignment mode: {}", other),
+                    },
                 },
                 PolicyType::ConsistentHashing => ConfigPolicyConfig::ConsistentHashing,
                 PolicyType::PrefixHash => ConfigPolicyConfig::PrefixHash {
@@ -640,6 +646,7 @@ impl Router {
         eviction_interval_secs = 120,
         max_tree_size = 2usize.pow(26),
         max_idle_secs = 14400,
+        assignment_mode = String::from("random"),
         max_payload_size = 512 * 1024 * 1024,
         dp_aware = false,
         api_key = None,
@@ -724,6 +731,7 @@ impl Router {
         eviction_interval_secs: u64,
         max_tree_size: usize,
         max_idle_secs: u64,
+        assignment_mode: String,
         max_payload_size: usize,
         dp_aware: bool,
         api_key: Option<String>,
@@ -821,6 +829,7 @@ impl Router {
             eviction_interval_secs,
             max_tree_size,
             max_idle_secs,
+            assignment_mode,
             max_payload_size,
             dp_aware,
             api_key,

sgl-model-gateway/bindings/python/src/sglang_router/router_args.py

@@ -36,6 +36,7 @@ class RouterArgs:
     eviction_interval_secs: int = 60
     max_tree_size: int = 2**26
     max_idle_secs: int = 4 * 3600
+    assignment_mode: str = "random"
     max_payload_size: int = 512 * 1024 * 1024  # 512MB default for large batches
     bucket_adjust_interval_secs: int = 5
     dp_aware: bool = False
@@ -310,6 +311,13 @@ class RouterArgs:
             default=RouterArgs.max_idle_secs,
             help="Maximum idle time in seconds before eviction (for manual policy)",
         )
+        routing_group.add_argument(
+            f"--{prefix}assignment-mode",
+            type=str,
+            default=RouterArgs.assignment_mode,
+            choices=["random", "min_load"],
+            help="Mode for assigning new routing keys in manual policy: random (default), min_load (worker with fewest requests)",
+        )
         routing_group.add_argument(
             f"--{prefix}max-payload-size",
             type=int,