gossiper: add is_alive that works on host_id

The function checks if a node with provided id is alive. If it fails to map id to ip
or there is no state for the ip found the node is considered to be dead.

gms/gossiper.cc

@@ -2410,6 +2410,30 @@ bool gossiper::is_alive(inet_address ep) const {
     return is_alive;
 }
 
+bool gossiper::is_alive(locator::host_id id) const {
+    auto ip_opt = _address_map.find(id);
+
+    if (!ip_opt) {
+        // if host ID is not in the gossiper state (and hence not in the address map) it is dead
+        return false;
+    }
+
+    auto ep = get_endpoint_state_ptr(*ip_opt);
+    if (!ep) {
+        // _address_map may have stale entry since we rely on gc to remove entries there
+        // FIXME: add function to address_map to remove immediately
+        return false;
+    }
+
+    if (id != ep->get_host_id()) {
+        // If IDs do not match it means that the node with provided ID was replaced
+        // with a new node with same IP address and hence it is dead
+        return false;
+    }
+
+    return is_alive(*ip_opt);
+}
+
 future<> gossiper::wait_alive(std::vector<gms::inet_address> nodes, std::chrono::milliseconds timeout) {
     return wait_alive([nodes = std::move(nodes)] { return nodes; }, timeout);
 }

gms/gossiper.hh

@@ -13,6 +13,7 @@
 #include <seastar/core/shared_ptr.hh>
 #include <seastar/core/gate.hh>
 #include <seastar/rpc/rpc_types.hh>
+#include "locator/host_id.hh"
 #include "utils/atomic_vector.hh"
 #include "utils/UUID.hh"
 #include "gms/generation-number.hh"
@@ -516,6 +517,8 @@ private:
 
 public:
     bool is_alive(inet_address ep) const;
+    bool is_alive(locator::host_id id) const;
+
     bool is_dead_state(const endpoint_state& eps) const;
     // Wait for nodes to be alive on all shards
     future<> wait_alive(std::vector<gms::inet_address> nodes, std::chrono::milliseconds timeout);