I've found OpenSearch to be a bit flaky but I haven't worked with it very seriously compared to ElasticSearch
(and before OpenSearch, the AWS-managed ElasticSearch absolutely hurt the ElasticSearch brand because of all of the issues Amazon created - it couldn't even rebalance shards, let alone add new nodes or switch to larger nodes without a blue-green deployment)
Elastic bought found.no, which became Elastic Cloud in 2015. That was years before Amazon forked Opensearch. The AWS hosted Elasticsearch emerged around the same time.
For most use-cases (indexing denormalised data as documents then running searches against them), there's little difference between the two. The mechanics of how the cluster operates are almost identical.
There are some Elasticsearch features that were part of X-Pack (their commercial offering) so aren't included in the OpenSearch fork. Some of those features are really nice to have and make life much easier; the enrich ingest processor is something I really miss in OpenSearch.
The biggest differences are in the tooling around Elasticsearch. All the observability stuff, the SIEM features, various integrations, and now the AI fluff. I've worked with clients in different sectors and - aside from the observability stuff (which is really nice) - none have had an appetite for any of that.
The OpenSearch team is doing some really cool stuff and the project has come a long way. I'm sure it'll continue to improve. It has a very loyal customer base and even has its own annual event; OpenSearchCon 2024 is next month!
Pure hearsay, but apparently ElasticSearch is considerably faster than OpenSearch. Would be good to compare the sources again, but I don't see any links to source on elastic.co yet.
I support both professionally. The last Apache licensed version of Elasticsearch was a very capable product and Opensearch inherits all of that. In the few years since the license change both products have evolved a little bit but the vast majority of those changes don't really matter to new users. Both products use the same core component, which is Apache Lucene; which powers all of the search features. If you are a new user, there is very little reason to prefer Elasticsearch over Opensearch. And this is confirmed by the fact that most of my new clients default to Opensearch.
The exception to this might be vector search, which is a relatively new feature that was implemented on both sides post fork. Lots of users want/need this. And both Elastic and Opensearch provide independent implementations with very similar feature sets. Both build on what Apache Lucene offers on this front. So there isn't a massive difference between the two. But I would give the advantage to Opensearch here since its implementation offers a bit more beyond just the Lucene support.
Kibana had a lot of closed source components before the fork already and Amazon fork of that is a bit more limited. But notably Amazon indeed re-implemented the security layer (before the fork actually), which on the Elastic side is a bit of a dumpster fire of complexity. In general I'm not impressed with the product from a usability point of view. Either on the Elastic or the Opensearch side. But the Elastic version is arguably a bit richer in features.
Some notable recent changes there include trying to introduce a new query language based on SQL and the whole fleet ecosystem (an agent based system) to get logging and other data into Elasticsearch. I don't think either is getting a lot of traction because of the licensing.
Are there any SMEs that have worked with both OpenSearch (the fork) and ElasticSearch? Are there significant differences?
I know the AWS fork had the big difference back then of having RBAC built into their Kibana portion.