How to Upgrade to Solr 9 on Acquia with Custom Configsets for Drupal

Staff Reporter

Metadrop’s guide by Fran Rouco walks Drupal teams through Acquia’s Solr 9 upgrade with a self-service path for tighter control of timing and custom configsets. Key shifts include Lucene 9 improvements, vector/KNN search, and stricter config rules: collections must be migrated to stateFormat=2 before upgrading, and <lib/> directives are opt-in in 9.8 (disabled by default). The article details generating Solr 9-compatible configsets with Search API Solr (≥ 4.3), why Acquia configsets differ from local ones, and a 7-step flow (with Drush) to delete/recreate indexes and reindex—scheduled with a brief search downtime.

Teams on Acquia can upload/validate custom configsets in Cloud Platform, then rebuild tracking and reindex to restore search. The takeaway: plan a maintenance window, use Acquia-sourced configsets, and verify caches/field types against Solr 9 defaults for a smooth cutover.

Reference: Solr9 upgrade on Acquia by Fran Rouco, Metadrop (10 September 2025)

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