If no broker from bootstrap.servers is available consumer retries indefinitely with debug log message :
DEBUG 17:16:13 Give up sending metadata request since no node is available
DEBUG 17:16:13 Initialize connection to node -1 for sending metadata request
DEBUG 17:16:13 Initiating connection to node -1 at localhost:9091.
At least, an ERROR message should be log after a number of retries.
In addition, maybe the consumer should fail in a such case ? This behavior could be set by a configuration property ?