Restarts of the elasticsearch service running on the logstash cluster are failing (it happened on logstah100[45] so far). The service command doesn't return since the elasticsearch service fails to shutdown. Guillaume filed a bug upstream at https://github.com/elastic/elasticsearch/issues/19829
Recent rolling restarts of elasticsearch on the search cluster went fine, so this is likely caused by a different workload on the logstash cluster. This didn't happen in the past when logstash* was still running Elastic 1.7.x