Web / Apache Solr Interview questions
What is the difference between Apache Solr and Elasticsearch?
Both are search platforms built on Apache Lucene and share the same underlying inverted-index fundamentals, but they diverge in ecosystem, API design, and operational model.
| Apache Solr | Elasticsearch |
| Fully open-source (Apache 2.0), governed by the Apache Software Foundation | Source-available under the Elastic license for recent versions, with OpenSearch as the Apache-licensed fork |
| Coordination via external Apache ZooKeeper (SolrCloud) | Built-in coordination and cluster state management |
| Config-file driven (solrconfig.xml, managed-schema) with a Schema API | Mapping and settings defined primarily through REST APIs and index templates |
| Strong, mature admin UI | Relies more on external tooling (Kibana) for visualization |
In practice, the choice often comes down more to ecosystem and team familiarity than raw capability: teams already invested in the ELK/Elastic stack (Kibana, Logstash) tend to pick Elasticsearch, while teams wanting a fully open-source license without usage restrictions, or already running ZooKeeper-based infrastructure, often prefer Solr. Both can handle large-scale full-text and faceted search well when properly tuned.
What coordination service does SolrCloud rely on that Elasticsearch does not require externally?
What do Solr and Elasticsearch share at their core?
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