I'm seeing connection failures using Sniffing ConnectionPool , where parts of the elasticsearch cluster is only available on the http port, that is - the transport port is closed for these nodes. When limiting the set of cluster nodes to only those with open transport ports, no failed sniffing cluster state errors occur.
So it seems that there is a requirement for the transport ports to be open, alternatively to set a publish port (which should be open to the client). If this is correct, you might want to add this to the documentation.
Elasticsearch.Net.PipelineException: Failed sniffing cluster state. ---> System.AggregateException: One or more errors occurred. ---> Elasticsearch.Net.PipelineException: An error occurred trying to read the response from the specified node. at Elasticsearch.Net.RequestPipeline.Sniff() in C:\Users\russ\source\elasticsearch-net-5.x\src\Elasticsearch.Net\Transport\Pipeline\RequestPipeline.cs:line 340
Thanks for the awesome work with the NEST language client for .Net.