Transform field types

When you migrate metadata to the Amazon OpenSearch Service domain or Amazon OpenSearch Serverless NextGen collection, the Metadata Migration phase rewrites index settings, mappings, templates, and aliases into a shape the target can accept. As part of this, it applies built-in field-type transformations that resolve version-specific field types that are deprecated or unsupported on newer engines. Most migrations are fully served by these built-in transformations, so start there and only add a custom transformer if a pilot run shows a field type the built-ins do not cover.

This page summarizes the built-in transformations, shows how to supply a custom JavaScript field-type transformer when the built-ins are not enough, recommends a sequence for introducing custom logic safely, and shows how to validate the transformed metadata on the target. Field-type transformation is part of the broader metadata migration phase — see Migrate metadata for how the phase fits into the overall workflow.