The Elasticsearch target works best with the BufferingWrapper target applied. By default the target assumes an Elasticsearch node is running on the localhost on port 9200.
See wiki for parameters.
<nlog>
<extensions>
<add assembly="NLog.Targets.ElasticSearch"/>
</extensions>
<targets>
<target name="elastic" xsi:type="BufferingWrapper" flushTimeout="5000">
<target xsi:type="ElasticSearch"/>
</target>
</targets>
<rules>
<logger name="*" minlevel="Info" writeTo="elastic" />
</rules>
</nlog>