[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.

[thinkharderdev]

Right, GB for GB ES is much easier to scale than Postgres (or any other DB) but probably also more expensive since ES is much more memory and compute hungry. But I can't say I have an apples-to-apples comparison since the use case for ES is usually "dump massive amounts of raw data in and index everything" which you wouldn't typically do with a Postgres instance. But in places where we have run large ES clusters my experience has not really been that it works without any user intervention (at least once you reach a certain scale) and that it involved a lot of operational support. Not that any other solution with comparable features would have been easier necessarily but still not easy in any absolute sense.