Elasticsearch

Elasticsearch is the industry-standard distributed search and analytics engine built on Apache Lucene. It powers full-text search (Wikipedia, GitHub, Stack Overflow), log aggregation (ELK Stack = Elasticsearch, Logstash, Kibana), real-time analytics, and emerging vector search (for AI/RAG). Elasticsearch index data with custom analyzers and mappings, query with Query DSL (declarative JSON), and scale horizontally across multiple nodes. In 2026, vector search via ESRE is emerging as new use case, AI applications storing embeddings for semantic search. Elasticsearch is NOT a primary database (no transactions, eventual consistency) but the default search/analytics layer for systems handling >100GB of data. Learning Elasticsearch is valuable for backend engineers building search features, SREs building observability platforms, and data engineers building analytics pipelines. The ELK Stack (Elasticsearch + Logstash + Kibana) is ubiquitous in enterprises; OpenSearch (AWS fork post-license change) is alternative but fundamentally similar.