Solr vs Elasticsearch vs OpenSearch: Which Should You Run?

Stay on Solr if your application is built on its query parsers and facets and the real problem is an old version. Move to Elasticsearch or OpenSearch only if you need something they offer that Solr does not, because a move is a rewrite of every query, facet and client call, not an upgrade. As of 31 October 2026, Solr 10.1.0 is the current release, and the Apache project lists every release below 9.11, including all of Solr 8, as end of life.

Most teams asking this question are not unhappy with search. They are running Solr 7 or 8, the project has moved on, and "should we just switch" sounds cheaper than an upgrade. It usually is not. If you want help costing either path, AceMQ's Apache Solr upgrade and migration service starts with a written inventory of what your application uses.

Solr is an Apache Software Foundation project, and its downloads page labels 10.x as the current stable line. Solr 9.11 is the last release in the 9.x series and may receive critical bugfix releases. Everything older is end of life, and the project warns that community help for those versions may be hard to get.

Solr 10 raises the floor. The Reference Guide says it needs Java 21 or higher, while SolrJ 10 needs Java 17. It also removes features some estates still use: HDFS index storage, the Prometheus exporter and JMX reporters (metrics moved to OpenTelemetry), PKI authentication v1, and the master and slave terminology in replication, which becomes leader and follower.

The cost of an upgrade is mostly the reindex, and the rule comes from Lucene: it keeps one major version of backward compatibility and refuses to open an index more than one major version old. The Solr guide says to reindex when moving between majors and to reindex whenever an index is more than one major version behind. So Solr 8 to 9 can be a rolling upgrade, but Solr 8 to 10 means building a new collection and switching an alias.

• Solr 8 to 9 rolling upgrade: the cluster must first be on 8.7 or newer, and SolrJ clients on 8.10 or newer if they use CloudSolrClient.
• Solr 8 to 10: reindex into a new collection, because the index is two majors old.
• From 9.10 on: SolrCloud nodes refuse to start if their version is lower than the highest in the cluster, so plan rollbacks as restores from backup, not rolling downgrades (the check can be switched off with SOLR_CLOUD_DOWNGRADE_ENABLED).
• Solr 10 specifics: solr.xml can no longer be loaded from ZooKeeper, and the Overseer can be disabled, a choice that cannot be changed during a rolling upgrade.

Most application queries need no rewrite, but check the 10.0 notes for removed field types (CurrencyField, ExternalFileField, EnumField), the removed HttpClient-based SolrJ clients and changed defaults such as the suggester lookup.

All three engines are built on Apache Lucene, so analyzers and relevance ideas carry over. Almost nothing else does. Solr's request parameters and JSON Facet API become the Query DSL and aggregations, SolrJ becomes another client library, fields become index mappings, and each analysis chain has to be rebuilt and tested against real queries. Nothing is copied across as files: you reindex from your source of truth or run both engines side by side with dual writes.

The cluster model changes too. SolrCloud uses a ZooKeeper ensemble. Elasticsearch and OpenSearch coordinate inside the cluster, and shard sizing and allocation become the main operational problem. Amazon OpenSearch Service is fully managed, so you tune through the domain configuration and APIs rather than on the nodes.

The two targets differ from each other in licence and governance. OpenSearch is Apache 2.0 under the OpenSearch Software Foundation; Elasticsearch's source added AGPLv3 as an option in 2024 while its default distribution stays under the Elastic License. AceMQ's OpenSearch vs Elasticsearch comparison sets out the differences with sources, and the Elasticsearch to OpenSearch migration guide covers moving between them.

• Stay and upgrade when the application depends on Solr features, the team knows Solr, and the trigger is an end-of-life version.
• Move to Elasticsearch when you already run Elastic for logs or security and want Kibana, Elastic's solutions or Elastic Cloud. See Elasticsearch consulting and support.
• Move to OpenSearch when you run on AWS and want Amazon OpenSearch Service, Apache 2.0 terms or a fully open security stack. See OpenSearch consulting and support.
• Do not move because Solr is old. An upgrade to 10 is smaller than a rewrite of every query.

Whichever you pick, cost it from an inventory: the query parsers, facets, analyzers and clients actually in use, and the reindex each path needs. A cluster that stays on Solr in the meantime still needs someone to answer when a replica will not recover; that is what 24/7 Apache Solr support covers.

• Apache Solr downloads page, solr.apache.org/downloads.html, read 31 October 2026.
• Apache Solr Reference Guide: System Requirements, Major Changes in Solr 10, Upgrade Notes and Reindexing pages (solr.apache.org/guide), read 31 October 2026.
• AceMQ, OpenSearch vs Elasticsearch, which cites Elastic, OpenSearch and Linux Foundation documentation checked in October 2026.