# Online index migration and shard scaling in OpenSearch with the AOSC plugin

DevFeed: [Online index migration and shard scaling in OpenSearch with the AOSC plugin](<https://devfeed.tech/articles/online-index-migration-and-shard-scaling-in-opensearch-with-the-aosc-plugin-12789.md>)

Original publisher: [Read original article](<https://opensearch.org/blog/online-index-migration-and-shard-scaling-in-opensearch-with-the-aosc-plugin/>)

Author: Arpit Singla

Published: 2026-08-18T21:56:28Z

Content type: article

Language: en

Sources: [OpenSearch](<https://devfeed.tech/sources/opensearch.md>)

Topics: [Amazon OpenSearch Service](<https://devfeed.tech/topics/amazon-opensearch-service.md>), [migration](<https://devfeed.tech/topics/migration.md>), [Open Source](<https://devfeed.tech/topics/open-source.md>), [Routing (disambiguation)](<https://devfeed.tech/topics/routing.md>)

Tags: [blog](<https://devfeed.tech/tags/blog.md>), [mapping](<https://devfeed.tech/tags/mapping.md>), [migration](<https://devfeed.tech/tags/migration.md>), [open-source](<https://devfeed.tech/tags/open-source.md>), [opensearch](<https://devfeed.tech/tags/opensearch.md>), [pipeline](<https://devfeed.tech/tags/pipeline.md>), [plugin](<https://devfeed.tech/tags/plugin.md>), [production](<https://devfeed.tech/tags/production.md>), [reconciliation](<https://devfeed.tech/tags/reconciliation.md>), [routing](<https://devfeed.tech/tags/routing.md>), [schema](<https://devfeed.tech/tags/schema.md>), [technical](<https://devfeed.tech/tags/technical.md>), [workflow](<https://devfeed.tech/tags/workflow.md>)

## AI overview

This article introduces Automatic Online Schema Change (AOSC), an open-source OpenSearch plugin for migrating live indexes to pre-created targets with different mappings, settings, shard counts, or document shapes. It backfills existing documents, replays operations made during migration, and switches an alias after a short write block, while documenting its scaling behavior and limitations.

## Source excerpt

Learn how the open-source AOSC plugin migrates live OpenSearch indexes--changing mappings, settings, or shard counts--without losing writes or requiring downtime. The post Online index migration and shard scaling in OpenSearch with the AOSC plugin appeared first on OpenSearch.