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After upgrading to OpenSearch 3.0.0, snapshot repositories on S3-compatible storage (e.g. Outscale) stopped working. The repository-s3 plugin in 3.0.0 upgraded the AWS SDK to 2.30.31, and testing a repository failed with: "Caused by: software.amazon.awssdk.services.s3.model.S3Exception: trailing checksum is not supported (Service: S3, Status Code: 400 ...)". The documented workaround of disabling checksum calculation via env vars did not help. Users confirmed the bug persisted in 3.1.0 and 3.2.0, blocking upgrades.

The 3.0.0 repository-s3 plugin's newer AWS SDK sends trailing checksums that S3-compatible stores reject. Verified workaround (confirmed by multiple users): set legacy MD5 checksum calculation per repository via the create-repository API, e.g. settings {"bucket": "bucketname", "basepath": "pathinbucket", "legacymd5checksumcalculation": "true"}. Permanent fix: maintainer cwperks raised PR #19788 to make this settable in opensearch.yml; it shipped in 3.3.2, where users confirmed s3.client.default.legacymd5checksumcalculation works without per-repo config. Resolution: upgrade to OpenSearch 3.3.2+ and set s3.client.default.legacymd5checksumcalculation: true, or apply the per-repository setting on older 3.x. (An earlier community workaround was rebuilding the repository-s3 plugin zip against AWS SDK 2.29.52.) Source: https://github.com/opensearch-project/OpenSearch/issues/18240

Source: https://github.com/opensearch-project/OpenSearch/issues/18240