feat: raise error if not 1 head instance created; privte ips from api

sky/provision/lambda_cloud/instance.py

@@ -118,9 +118,11 @@ def launch_nodes(node_type: str, quantity: int):
             raise
 
     if head_instance_id is None:
-        instance_id = launch_nodes('head', 1)[0]
-        created_instance_ids.append(instance_id)
-        head_instance_id = instance_id
+        instance_ids = launch_nodes('head', 1)
+        if len(instance_ids) != 1:
+            raise RuntimeError(f"Expected exactly one instance, got {len(instance_ids)}")
+        created_instance_ids.append(instance_ids[0])
+        head_instance_id = instance_ids[0]
 
     assert head_instance_id is not None, 'head_instance_id should not be None'
 
@@ -201,10 +203,8 @@ def get_cluster_info(
         instances[instance_id] = [
             common.InstanceInfo(
                 instance_id=instance_id,
-                # TODO (kmushegi): check if this is correct;
-                # external ip is preferred
-                internal_ip='',
-                external_ip=instance_info['ip'],
+                internal_ip=instance_info["private_ip"],
+                external_ip=instance_info["ip"],
                 ssh_port=22,
                 tags={},
             )