support dp attn with client lb (#33105)

Co-authored-by: Kan Wu <wukanustc@gmail.com>

python/sglang/srt/managers/rust_server.py

@@ -76,6 +76,13 @@ class RustServer:
                 "drop --preferred-sampling-params and send those values per request."
             )
         http_addr = f"{server_args.host}:{server_args.port}"
+
+        # Per-DP-rank HTTP port with client load balancing. `None` when DP is off,
+        # so the rank is not conflated with rank 0 of a one-rank group.
+        dp_rank = scheduler.ps.attn_dp_rank if scheduler.ps.dp_size > 1 else None
+        if dp_rank is not None:
+            http_addr = f"{server_args.host}:{server_args.port + dp_rank}"
+
         launch_cores, server_cores = cls._partition_cores()
 
         server = Server(
@@ -93,9 +100,15 @@ class RustServer:
             except OSError as e:
                 logger.warning("rust server: cannot pin scheduler launch thread: %s", e)
 
+        # Under DP every rank runs its own server on its own port, so the rank is
+        # what tells two otherwise identical startup lines apart.
+        dp_note = (
+            "" if dp_rank is None else f" (DP rank {dp_rank}/{scheduler.ps.dp_size})"
+        )
         logger.info(
-            "SGLANG_RUST_SERVER enabled, Rust server listen on %s",
+            "SGLANG_RUST_SERVER enabled, Rust server listen on %s%s",
             http_addr,
+            dp_note,
         )
 
         return cls(server)

python/sglang/srt/server_args.py

@@ -9332,6 +9332,10 @@ class PortArgs:
             if dp_rank is None:
                 # TokenizerManager to DataParallelController
                 scheduler_input_port = port_base + 4
+            elif is_rust_server:
+                # Rust server path (SGLANG_RUST_SERVER + dp attention): there is no
+                # DataParallelController allocating worker ports.
+                scheduler_input_port = port_base + 6 + dp_rank
             else:
                 assert worker_ports is not None
                 scheduler_input_port = worker_ports[dp_rank]