Comment by jturpin

Elasticsearch has built in horizontal scaling abilities, unlike Postgres/other SQL databases. It also has integrations with cloud providers for peer discovery, or can use DNS. Once a new data node is detected and reachable, the masters will start sending it shards of data, distributing the load. This all happens without any user intervention. I can't really speak to cost, it is somewhat easy to blow up the memory usage in Elastic for sure, but I can't say its been more expensive than similarly sized Postgres clusters.