The one area where Elasticsearch shines is distributed search. It was built from the ground up to be suitable for high-scale 'cloud' applications.
There are many features Elasticsearch has as a result of being designed to be distributed that aren't currently available in Solr, such as:
- Shards and replicas can to moved to any node in the cluster on demand.
- With a simple API call you can increase and decrease the number of replicas without the need of shutting down nodes or creating new nodes.
- Manipulate shard placement with the cluster reroute API on a live cluster.
- Search across multiple indexes.
- Change the schema without restarting the server.
- Automatic shard rebalancing
Elasticsearch also has a module called Gateway, that in the case of the whole cluster crashing or being taken down will enable you to easily restore the latest state of the cluster when it gets back up.
Services such as Bonsai further simplify scaling Elasticsearch by hosting and scaling the search servers for you, making it nearly as easy to get started as CloudSearch or Searchify. Elasticsearch was also specifically designed to run well and be relatively easy to setup on EC2.