I'm curious about the recommendation put forth in https://www.elastic.co/blog/how-many-shards-should-i-have-in-my-elasticsearch-cluster, specifically that
A good rule-of-thumb is to ensure you keep the number of shards per node below 20 per GB heap it has configured. A node with a 30GB heap should therefore have a maximum of 600 shards, but the further below this limit you can keep it the better. This will generally help the cluster stay in good health.
I've definitely seen the total count of shards in a cluster affect master node performance, but I'm curious what evidence or benchmarking would lead to the per-datanode recommendation. I'm mainly trying to determine if alerting on this metric is needed as a trigger for scaling a cluster.