snitch: Export prefer-local

The boolean bit says whether "the system" should prefer connecting to
the address gossiper around via INTERNAL_IP. Currently only gossiping
property file snitch allows to tune it and ec2-multiregion snitch
prefers internal IP unconditionally.

So exporting consists of 2 pieces:

- add prefer_local() snitch method that's false by default or returns
  the (existing) _prefer_local bit for production snitch base
- set the _prefer_local to true by ec2-multiregion snitch

While at it the _prefer_local is moved to production_snitch_base for
uniformity with the new prefer_local() call

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

locator/ec2_multi_region_snitch.cc

@@ -27,7 +27,7 @@ future<> ec2_multi_region_snitch::start() {
     _state = snitch_state::initializing;
 
     return seastar::async([this] {
-        ec2_snitch::load_config().get();
+        ec2_snitch::load_config(true).get();
         if (this_shard_id() == io_cpu_id()) {
             inet_address local_public_address;
 

locator/ec2_snitch.cc

@@ -17,11 +17,11 @@ ec2_snitch::ec2_snitch(const snitch_config& cfg) : production_snitch_base(cfg) {
  *
  * @return
  */
-future<> ec2_snitch::load_config() {
+future<> ec2_snitch::load_config(bool prefer_local) {
     using namespace boost::algorithm;
 
     if (this_shard_id() == io_cpu_id()) {
-        return aws_api_call(AWS_QUERY_SERVER_ADDR, AWS_QUERY_SERVER_PORT, ZONE_NAME_QUERY_REQ).then([this](sstring az) {
+        return aws_api_call(AWS_QUERY_SERVER_ADDR, AWS_QUERY_SERVER_PORT, ZONE_NAME_QUERY_REQ).then([this, prefer_local](sstring az) {
             assert(az.size());
 
             std::vector<std::string> splits;
@@ -38,12 +38,15 @@ future<> ec2_snitch::load_config() {
                 _my_dc = az.substr(0, az.size() - 3);
             }
 
-            return read_property_file().then([this] (sstring datacenter_suffix) {
+            _prefer_local = prefer_local;
+
+            return read_property_file().then([this, prefer_local] (sstring datacenter_suffix) {
                 _my_dc += datacenter_suffix;
                 logger().info("Ec2Snitch using region: {}, zone: {}.", _my_dc, _my_rack);
 
-                return container().invoke_on_others([this] (snitch_ptr& local_s) {
+                return container().invoke_on_others([this, prefer_local] (snitch_ptr& local_s) {
                     local_s->set_my_dc_and_rack(_my_dc, _my_rack);
+                    local_s->set_prefer_local(prefer_local);
                 });
             });
         });
@@ -55,7 +58,7 @@ future<> ec2_snitch::load_config() {
 future<> ec2_snitch::start() {
     _state = snitch_state::initializing;
 
-    return load_config().then([this] {
+    return load_config(false).then([this] {
         set_snitch_ready();
     });
 }

locator/ec2_snitch.hh

@@ -23,7 +23,7 @@ public:
         return "org.apache.cassandra.locator.Ec2Snitch";
     }
 protected:
-    future<> load_config();
+    future<> load_config(bool prefer_local);
     future<sstring> aws_api_call(sstring addr, uint16_t port, const sstring cmd);
     future<sstring> read_property_file();
 private:

locator/production_snitch_base.hh

@@ -54,6 +54,10 @@ private:
     virtual void set_prefer_local(bool prefer_local) override;
     void parse_property_file();
 
+    virtual bool prefer_local() const noexcept override {
+        return _prefer_local;
+    }
+
 protected:
     /**
      * Loads the contents of the property file into the map
@@ -95,5 +99,7 @@ protected:
 private:
     size_t _prop_file_size;
     snitch_ptr* _backreference = nullptr;
+protected:
+    bool _prefer_local = false;
 };
 } // namespace locator

locator/snitch_base.hh

@@ -169,6 +169,11 @@ public:
         return snitch_signal_connection_t();
     }
 
+    // tells wheter the INTERNAL_IP address should be preferred over endpoint address
+    virtual bool prefer_local() const noexcept {
+        return false;
+    }
+
     static logging::logger& logger() {
         static logging::logger snitch_logger("snitch_logger");
         return snitch_logger;
@@ -348,7 +353,6 @@ private:
 protected:
     sstring _my_dc;
     sstring _my_rack;
-    bool _prefer_local = false;
 };
 
 } // namespace locator