Cross-Region S3 Replication Without the Gotchas (2026)
Cross-Region S3 Replication Without the Gotchas (2026) Cross-region S3 replication copies objects from a source bucket to a destination in another region, continuously. AWS S3, MinIO, and RustFS all do it, but the failures almost never come from the copy itself. They come from versioning, IAM, and delete-marker defaults you forgot to set. Key facts before you start Check What the official docs…
Cross-region S3 replication is a feature that automatically copies new objects from a source bucket in one region to a destination bucket in another region. The process is asynchronous, meaning that the source bucket acknowledges the write before the destination bucket receives the copy, resulting in eventual consistency rather than real-time synchronization.
This functionality is supported by various systems, including AWS S3, MinIO, and RustFS, which are used for disaster recovery and to provide faster access to data for users in different regions.
However, several often-overlooked details can cause replication to fail silently. The first critical requirement is versioning, which must be enabled on both the source and destination buckets. If versioning is not enabled on either side, the replication process will not function. Additionally, objects that are written before the replication configuration is applied will not be replicated. To address this, tools like S3 Batch Replication can be used to backfill these pre-existing objects.
In terms of permissions, the AWS IAM role used by replication needs specific S3 actions, totaling seven different actions. These include GetReplicationConfiguration, ListBucket, GetObjectVersionForReplication, Acl, and Tagging, as well as ReplicateObject, Delete, and Tags actions. The IAM role also requires a trust policy that allows s3.amazonaws.com to assume the role.
A common mistake is to miss one of these actions or to omit the principal s3.amazonaws.com in the trust policy, leading to silent failures where replication does not occur.
To correctly set up the IAM role and avoid silent failures, the trust policy must include s3.amazonaws.com, and the permissions policy must grant the full set of replication actions. Any omission can result in the absence of data in the destination bucket with no error messages to indicate what went wrong.
The final step involves attaching a replication configuration file, typically in JSON format, to the source bucket using the AWS CLI command. The minimal replication configuration includes specifying the role used for replication and defining the destination bucket. A common mistake is to leave the filter prefix empty, meaning "all objects," which can inadvertently replicate all data, including objects that were not intended to be replicated.
Additionally, the priority of the replication rule must be set, especially when multiple rules are defined.
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