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Amazon S3’s Object Lock feature enables you to enforce a write-once-read-many (WORM) model, ensuring complete data immutability. By preventing objects from being permanently deleted or overwritten, Object Lock helps you meet stringent regulatory and compliance requirements.
The image describes "Object Lock," highlighting its features: preventing permanent data deletion or overwriting, meeting regulatory requirements, and enforcing a write-once-read-many (WORM) model.

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How Object Lock Works

You can apply Object Lock at two levels:
  1. Object-level – Lock individual objects when you upload them.
  2. Bucket-level rule – Automatically lock every new object in the bucket.
Once locked, objects cannot be deleted or altered until the retention period expires (or until you remove a legal hold).

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Use Case: Financial Records Retention

Regulated industries—such as banking and insurance—must often retain records for a defined period. With Object Lock, you can specify exactly how long data must remain immutable.
The image shows a diagram with a blue building icon on the left, an arrow labeled "5 Years" pointing to a green bucket icon on the right, under the title "Object Lock."
For example, enforcing a five-year retention period ensures that critical financial records remain tamper-proof until that timeframe ends.

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Object Lock Modes

Choose one of two retention modes when locking an object:
ModeDescriptionRequired Permission
Governance ModeMost users are blocked from deleting or overwriting. Principals with bypass rights can modify.s3:BypassGovernanceRetention
Compliance ModeAll users—including the root user—are blocked from deleting or shortening retention.None (only AWS account deletion)
Governance Mode lets security admins with the s3:BypassGovernanceRetention permission perform emergency deletions if needed.
Compliance Mode guarantees unbreakable WORM protection—for any removal, you must delete the entire AWS account.
The image illustrates two object lock modes: Governance Mode, where most users are restricted but users with bypass rights can access, and Compliance Mode, where all users, including root users, are restricted during the retention period.
When the exact retention period is unknown—such as during active litigation—you can apply a Legal Hold. This disables object deletion or modification indefinitely until the hold is lifted. Only principals with the s3:PutObjectLegalHold permission can remove a Legal Hold. 
aws s3api put-object-legal-hold \
  --bucket my-bucket \
  --key important-document.pdf \
  --legal-hold Status=ON
The image illustrates a "Legal Hold" process, showing that only users with "PutObjectLegalHold" permission can interact with a storage bucket, while regular users cannot. It includes a use case for documents used during active litigation.

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Prerequisites

Object Lock must be enabled at bucket creation and cannot be turned on afterward.
Ensure Versioning is also enabled on the same bucket.
  • Enable Versioning on your S3 bucket.
  • Enable Object Lock when you create the bucket.
The image provides instructions for using "Object Lock," stating that versioning and object locking must be enabled in the bucket.
Once both settings are enabled, you can configure retention periods, switch modes, and apply Legal Holds to satisfy compliance mandates.

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References

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