Amazon OpenSearch Service

OpenSearch is an open source search and analytics engine, the technology behind the search box of many websites. Amazon OpenSearch Service runs it for you on AWS: you get a cluster that stays patched and backed up, and you send it documents to make searchable. It grew out of Elasticsearch, and the service was called Amazon Elasticsearch Service until 2021.

Its core is an inverted index: for every word, a list of the documents where it appears, like the index at the back of a book. That is why it can search millions of product descriptions for "red running shoes" in milliseconds, tolerate typos, and rank the results by relevance, things a regular database does poorly.

The other big use is logs. Apps and servers produce endless lines of text, and teams send them to OpenSearch to search for an error message, count failures per minute, or build charts in OpenSearch Dashboards, its visual tool. More recently it is also used for vector search, finding documents by meaning rather than exact words, which is a common piece of RAG systems. A serverless option scales capacity without managing a cluster.