We want to increase the nodes dynamically when we need to increase based on our production load.
Just a thought. We never implemented an automatic cluster sizing on cloud.elastic.co and I think there are very good reasons for that. One of the reasons I believe is that I don't want my cluster to rebalance all the shards all the time.
I'd prefer sending "alerts" and then ask a ops to do the job if really needed.
Just my 0.05 cents.