fix(prefill): IPv6-ready bootstrap host resolution for sglang (#3019)

Signed-off-by: Dmitrii Gabor <dmitryg1709@gmail.com>
Co-authored-by: ishandhanani <82981111+ishandhanani@users.noreply.github.com>

components/src/dynamo/sglang/request_handlers/handler_base.py

@@ -110,12 +110,40 @@ class BaseWorkerHandler(ABC):
         bootstrap_port = inner_tm.server_args.disaggregation_bootstrap_port
 
         if inner_tm.server_args.dist_init_addr:
-            bootstrap_host = socket.gethostbyname(
-                inner_tm.server_args.dist_init_addr.split(":")[0]
-            )
+            # IPv6-ready host extraction and resolution:
+            # 1) Extract raw host from "host:port" or "[IPv6]:port"/"[IPv6]".
+            # 2) Resolve via AF_UNSPEC to accept A/AAAA and literals.
+            # 3) Bracket-wrap IPv6 for safe "{host}:{port}" URL formatting.
+            addr = inner_tm.server_args.dist_init_addr.strip()
+            if addr.startswith("["):
+                end = addr.find("]")
+                host_core = addr[1:end] if end != -1 else addr.strip("[]")
+            else:
+                # Only treat single ':' with numeric suffix as host:port; otherwise it's an IPv6/FQDN host.
+                if addr.count(":") == 1:
+                    host_candidate, maybe_port = addr.rsplit(":", 1)
+                    host_core = host_candidate if maybe_port.isdigit() else addr
+                else:
+                    host_core = addr
+            try:
+                infos = socket.getaddrinfo(
+                    host_core,
+                    None,
+                    family=socket.AF_UNSPEC,
+                    type=socket.SOCK_STREAM,
+                )
+                resolved = infos[0][4][0]  # let OS policy pick v4/v6
+                bootstrap_host = resolved
+            except socket.gaierror:
+                # Fallback: keep literal/FQDN as-is (still wrap IPv6 below)
+                bootstrap_host = host_core
         else:
             bootstrap_host = get_local_ip_auto()
 
+        # Wrap IPv6 literal with brackets so f"{host}:{port}" stays valid.
+        if ":" in bootstrap_host and not bootstrap_host.startswith("["):
+            bootstrap_host = f"[{bootstrap_host}]"
+
         return bootstrap_host, bootstrap_port
 
     def _propagate_trace_context_to_sglang(