Going to port the Nginx plus metrics from Nginxbeat to Metricbeat, I wonder if we need to split the nested metrics (see https://github.com/mrkschan/nginxbeat/#exported-fields) in Metricbeat as well. Does Kibnana support viewing nested document now?
We initially tried to work with some nested documents but we came to the conclusion that it is much easier and more powerful to create separate metricsets. In the nginx case I recommend to create one metricset for each type you have listed on the page.
Be aware that there are also 2 types of Fetch interfaces. One that returns just one event and one that returns a list of events as this is sometimes needed (for example we use it in system/processes). For each process one event is stored, but still all process events have the same timestamp.
In your example, tcpupstream peers is such an example. tcpupstream could be sent without the peers itself but the number of peers. An peers which a separate metricset sends and event for each peer.