The replica set member host changed for itself from server IP address to hostname

chris · December 2, 2022, 2:28pm

The initiate is using the servers own hostname as returned by the OS.

class CmdReplSetInitiate : public ReplSetCommand

mongodb/mongo/blob/e79fa3438f0fe33a4e688e29fad0a161a8681523/src/mongo/db/repl/repl_set_commands.cpp#L339


      
                      seeds->push_back(m);
                  }
                  if (*comma == 0) {
                      break;
                  }
                  p = comma + 1;
              }
          }
          }  // namespace
          
          class CmdReplSetInitiate : public ReplSetCommand {
          public:
              CmdReplSetInitiate() : ReplSetCommand("replSetInitiate") {}
              std::string help() const override {
                  return "Initiate/christen a replica set.\n"
                         "http://dochub.mongodb.org/core/replicasetcommands";
              }
              virtual bool run(OperationContext* opCtx,
                               const DatabaseName&,
                               const BSONObj& cmdObj,
                               BSONObjBuilder& result) {

HostAndPort me = someHostAndPortForMe();

github.com

mongodb/mongo/blob/e79fa3438f0fe33a4e688e29fad0a161a8681523/src/mongo/db/repl/repl_set_commands.cpp#L390


      
              StorageInterface::get(opCtx),
              ReplicationProcess::get(opCtx));
          std::string name;
          std::vector<HostAndPort> seeds;
          parseReplSetSeedList(&externalState, replSetString, &name, &seeds);  // may throw...
          
          BSONObjBuilder b;
          b.append("_id", name);
          b.append("version", 1);
          BSONObjBuilder members;
          HostAndPort me = someHostAndPortForMe();
          
          auto appendMember =
              [&members, serial = DecimalCounter<uint32_t>()](const HostAndPort& host) mutable {
                  members.append(
                      StringData{serial},
                      BSON("_id" << static_cast<int>(serial) << "host" << host.toString()));
                  ++serial;
              };
          appendMember(me);
          result.append("me", me.toString());

Which eventually leads to the call of getHostName() in someHostAndPortForMe():

github.com

mongodb/mongo/blob/e79fa3438f0fe33a4e688e29fad0a161a8681523/src/mongo/db/repl/repl_set_commands.cpp#L281


      
              if (localhost_only) {
                  // We're only binding localhost-type interfaces.
                  // Use one of those by name if available,
                  // otherwise fall back on "localhost".
                  return HostAndPort(addrs.size() ? addrs[0] : "localhost", bind_port);
              }
          
              // Based on the above logic, this is only reached for --bind_ip '0.0.0.0'.
              // We are listening externally, but we don't have a definite hostname.
              // Ask the OS.
              std::string h = getHostName();
              verify(!h.empty());
              verify(h != "localhost");
              return HostAndPort(h, serverGlobalParams.port);
          }
          
          void parseReplSetSeedList(ReplicationCoordinatorExternalState* externalState,
                                    const std::string& replSetString,
                                    std::string* setname,
                                    std::vector<HostAndPort>* seeds) {
              const char* p = replSetString.c_str();