ElasticSearch output plugin to support multiple hosts and enhance stability 

ElasticSearch output plugin to support multiple hosts and enhance stability
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1. Make elasticSearch output plugin to support mutiple hosts and round robin balance, which will help a lot to balance the resource and performance of whole elasticsearch cluster.
2. Improve stability by handling exception and retry with left servers while flushing bulk, which will reduce the possibility of data loss largely.
Yes, I have the same concern too but in most common cases, as the simplest solution, we may prefer little duplication instead of data loss especially for non high-precision data like log.