Logstash fails to send events to ES when one instance of cluster stops


I have this config. Logstash (2.3*) and ES (2.1.1).

Logstash ES output are configured with two ES servers in cluster: hosts => ["",""]

There are 2 ES instances in this IPs configured in a cluster. When I stop one of the servers, Logstash stops to index events while one of the nodes are down.
Error that I'm getting from ES:
message=>"Attempted to send a bulk request to Elasticsearch configured at '["", ""]', but an error occurred and it failed! Are you sure you can reach elasticsearch from this machine using the configuration provided?", :error_message=>" failed to respond", :error_class=>"Manticore::ClientProtocolException"

Logstash stops to send events to ES. Why I'm getting this error if the other instance of ES is up and running?