Opensearch

OpenSearch is the AWS-backed open-source fork of Elasticsearch, maintaining API compatibility while providing an independently governed alternative to Elastic's licensing changes. For agents in AWS environments or teams that require open-source licensing for their search infrastructure, OpenSearch provides full-featured search and analytics with the same REST API patterns as Elasticsearch. Amazon OpenSearch Service offers the managed cloud deployment with AWS-native security integration.

The REST API is compatible with Elasticsearch APIs, covering document indexing, search queries (full-text, structured, semantic with k-NN), aggregations, index management, and cluster operations. Agents built for Elasticsearch can typically be pointed at OpenSearch with minimal changes. The k-NN plugin adds vector search capabilities for semantic search use cases alongside traditional full-text search.

Authentication for Amazon OpenSearch Service uses AWS IAM with fine-grained access control for index-level permissions. Self-hosted OpenSearch uses its own Security plugin with user management and role-based access control. The auth model differs between managed (AWS IAM) and self-hosted (internal security plugin) deployments — teams should plan their auth architecture based on their deployment model.

Reliability for Amazon OpenSearch Service is AWS-managed with high-availability cluster configurations. Self-hosted OpenSearch reliability is the team's operational responsibility. The distributed cluster architecture handles node failures gracefully when configured correctly. Teams running OpenSearch for production search infrastructure should plan shard counts and replica configurations appropriate for their availability requirements.

Documentation is thorough and maintained at opensearch.org with additional AWS-specific documentation for the managed service. Teams familiar with Elasticsearch documentation will find OpenSearch documentation immediately recognizable — the API compatibility extends to documentation patterns. AWS-specific configuration documentation supplements the core OpenSearch documentation for managed service deployments.