(mongodb >=1.13.0)
The MongoDB\Driver\ServerDescription class is a value object that represents a server to which the driver is connected. Instances of this class are returned by MongoDB\Driver\Server::getServerDescription() and MongoDB\Driver\Monitoring\ServerChangedEvent methods.
MongoDB\Driver\ServerDescription::TYPE_UNKNOWN
Unknown server type, returned by MongoDB\Driver\ServerDescription::getType().
MongoDB\Driver\ServerDescription::TYPE_STANDALONE
Standalone server type, returned by MongoDB\Driver\ServerDescription::getType().
MongoDB\Driver\ServerDescription::TYPE_MONGOS
Mongos server type, returned by MongoDB\Driver\ServerDescription::getType().
MongoDB\Driver\ServerDescription::TYPE_POSSIBLE_PRIMARY
Replica set possible primary server type, returned by MongoDB\Driver\ServerDescription::getType().
A server may be identified as a possible primary if it has not yet been checked but another memory of the replica set thinks it is the primary.
MongoDB\Driver\ServerDescription::TYPE_RS_PRIMARY
Replica set primary server type, returned by MongoDB\Driver\ServerDescription::getType().
MongoDB\Driver\ServerDescription::TYPE_RS_SECONDARY
Replica set secondary server type, returned by MongoDB\Driver\ServerDescription::getType().
MongoDB\Driver\ServerDescription::TYPE_RS_ARBITER
Replica set arbiter server type, returned by MongoDB\Driver\ServerDescription::getType().
MongoDB\Driver\ServerDescription::TYPE_RS_OTHER
Replica set other server type, returned by MongoDB\Driver\ServerDescription::getType().
Such servers may be hidden, starting up, or recovering. They cannot be queried, but their hosts lists are useful for discovering the current replica set configuration.
MongoDB\Driver\ServerDescription::TYPE_RS_GHOST
Replica set ghost server type, returned by MongoDB\Driver\ServerDescription::getType().
Servers may be identified as such in at least three situations: briefly during server startup; in an uninitialized replica set; or when the server is shunned (i.e. removed from the replica set config). They cannot be queried, nor can their host list be used to discover the current replica set configuration; however, the client may monitor this server in hope that it transitions to a more useful state.
MongoDB\Driver\ServerDescription::TYPE_LOAD_BALANCER
Load balancer server type, returned by MongoDB\Driver\ServerDescription::getType().