diff --git a/Makefile b/Makefile
index b5622a9..dd68dfb 100644
--- a/Makefile
+++ b/Makefile
@@ -18,11 +18,20 @@ endif
 
 WARN = -Wall -Wno-unused-function -finline-functions -Wno-sign-compare #-Wconversion
 INCPATH = -I./src -I$(THIRD_PATH)/include
+<<<<<<< HEAD
+CFLAGS = -std=c++0x $(WARN) $(OPT) $(INCPATH)
+LDFLAGS += $(THIRD_LIB) -lpthread
+OS := $(shell uname -s)
+ifeq ($(OS),Linux)
+	LFLAGS += -lrt
+endif
+=======
 CFLAGS = -std=c++0x $(WARN) $(OPT) $(INCPATH) $(EXTRA_CFLAGS)
 ifeq ($(USE_S3), 1)
 CFLAGS += -DUSE_S3=1
 endif
 LDFLAGS = $(EXTRA_LDFLAGS) $(THIRD_LIB) -lpthread # -lrt
+>>>>>>> upstream/master
 
 PS_LIB = build/libps.a
 PS_MAIN = build/libpsmain.a
diff --git a/src/system/dashboard.cc b/src/system/dashboard.cc
index 3e66962..a1348e5 100644
--- a/src/system/dashboard.cc
+++ b/src/system/dashboard.cc
@@ -3,7 +3,7 @@
 
 namespace PS {
 
-bool NodeIDCmp::operator()(const NodeID& a, const NodeID& b) {
+bool NodeIDCmp::operator()(const NodeID& a, const NodeID& b) const {
   string a_primary, a_secondary;
   splitNodeID(a, a_primary, a_secondary);
   string b_primary, b_secondary;
@@ -17,7 +17,7 @@ bool NodeIDCmp::operator()(const NodeID& a, const NodeID& b) {
   }
 }
 
-void NodeIDCmp::splitNodeID(const NodeID& in, string& primary, string& secondary) {
+void NodeIDCmp::splitNodeID(const NodeID& in, string& primary, string& secondary) const {
   size_t tailing_alpha_idx = in.find_last_not_of("0123456789");
   if (std::string::npos == tailing_alpha_idx) {
     primary = in;
diff --git a/src/system/dashboard.h b/src/system/dashboard.h
index 1cff3b8..5054257 100644
--- a/src/system/dashboard.h
+++ b/src/system/dashboard.h
@@ -5,8 +5,8 @@
 namespace PS {
 
 struct NodeIDCmp {
-  void splitNodeID(const NodeID& in, string& primary, string& secondary);
-  bool operator()(const NodeID& a, const NodeID& b);
+  void splitNodeID(const NodeID& in, string& primary, string& secondary) const;
+  bool operator()(const NodeID& a, const NodeID& b) const;
 };
 
 class Dashboard {
diff --git a/src/system/postoffice.cc b/src/system/postoffice.cc
index 9b47588..5dfc8dd 100644
--- a/src/system/postoffice.cc
+++ b/src/system/postoffice.cc
@@ -115,6 +115,59 @@ void Postoffice::Recv() {
   }
 }
 
+<<<<<<< HEAD
+void Postoffice::manageNode(Task& tk) {
+  CHECK(tk.has_mng_node());
+  auto& mng = tk.mng_node();
+  switch (mng.cmd()) {
+    case ManageNode::CONNECT: {
+      CHECK(IamScheduler());
+      CHECK_EQ(mng.node_size(), 1);
+      // first add this node into app
+      Task add = tk;
+      add.set_customer(CHECK_NOTNULL(app_)->name());
+      add.mutable_mng_node()->set_cmd(ManageNode::ADD);
+      manageNode(add);
+      // create the app in this node
+      Task task;
+      task.set_request(true);
+      task.set_customer(app_->name());
+      task.set_type(Task::MANAGE);
+      task.set_time(1);
+      task.mutable_mng_app()->set_cmd(ManageApp::ADD);
+      task.mutable_mng_app()->set_conf(app_conf_);
+      app_->port(mng.node(0).id())->submit(task);
+      // check if all nodes are connected
+      if (yp().num_workers() >= FLAGS_num_workers &&
+          yp().num_servers() >= FLAGS_num_servers) {
+        nodes_are_ready_.set_value();
+      }
+      tk.set_customer(app_->name());  // otherwise the remote node doesn't know
+      // how to find the according customer
+      break;
+    }
+    case ManageNode::ADD:
+    case ManageNode::UPDATE: {
+      auto obj = yp().customer(tk.customer());
+      CHECK(obj) << "customer [" << tk.customer() << "] doesn't exists";
+      for (int i = 0; i < mng.node_size(); ++i) {
+        auto node = mng.node(i);
+        yp().addNode(node);
+        obj->exec().add(node);
+        for (auto c : yp().children(obj->name())) {
+          auto child = yp().customer(c);
+          if (child) child->exec().add(node);
+        }
+      }
+      break;
+    }
+    case ManageNode::REPLACE: {
+      break;
+    }
+    case ManageNode::REMOVE: {
+      break;
+    }
+=======
 bool Postoffice::Process(Message* msg) {
   if (!msg->task.request()) manager_.AddResponse(msg);
   // process this message
@@ -126,6 +179,7 @@ bool Postoffice::Process(Message* msg) {
     int id = msg->task.customer_id();
     // let the executor to delete "msg"
     manager_.customer(id)->executor()->Accept(msg);
+>>>>>>> upstream/master
   }
   return true;
 }
diff --git a/src/system/yellow_pages.h b/src/system/yellow_pages.h
new file mode 100644
index 0000000..81c652e
--- /dev/null
+++ b/src/system/yellow_pages.h
@@ -0,0 +1,57 @@
+#pragma once
+
+#include "util/common.h"
+#include "system/proto/node.pb.h"
+#include "system/van.h"
+
+namespace PS {
+
+class Customer;
+typedef shared_ptr<Customer> CustomerPtr;
+class NodeGroup;
+
+// maintain inforamations about nodes and customers
+class YellowPages {
+ public:
+  YellowPages() { }
+  ~YellowPages();
+  void init() { van_.init(); }
+
+  // manage customers
+  void addCustomer(Customer* obj);
+  // ask the system to delete the customer
+  void depositCustomer(const string& name);
+  void removeCustomer(const string& name);
+  Customer* customer(const string& name);
+
+  void addRelation(const string& child, const string& parent) {
+    relations_[parent].push_back(child);
+  }
+  const std::vector<string>& children(const string& parent) {
+    return relations_[parent];
+  }
+
+  // manage nodes
+  void addNode(const Node& node);
+  void removeNode(const Node& node);
+
+  int num_workers() { return num_workers_; }
+  int num_servers() { return num_servers_; }
+  std::vector<Node> nodes();
+
+  Van& van() { return van_; }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(YellowPages);
+  int num_workers_ = 0;
+  int num_servers_ = 0;
+
+  std::map<NodeID, Node> nodes_;
+  std::map<string, std::pair<Customer*, bool>> customers_;
+
+  // parent vs children
+  std::unordered_map<string, std::vector<string>> relations_;
+  Van van_;
+};
+
+} // namespace PS