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Versioning enables you to keep multiple versions of an object in one bucket. You must explicitly enable versioning on your bucket. By default versioning is disabled. Regardless of whether you have enabled versioning on your bucket or not, each object has a version ID. If you have not enabled versioning on your bucket, then Amazon S3 sets the version ID value null. If you have enabled versioning on your bucket, Amazon S3 assigns a unique version ID value for the object.
Versioning enables you to keep multiple versions of an object in one bucket, for
my-image.jpg (version 111111) and
my-image.jpg (version 222222). You might enable versioning to
recover from unintended overwrites and deletions or to archive objects so that you
can retrieve previous versions of them.
The SOAP API does not support Versioning.
When you enable versioning on a bucket, existing objects, if any, in the bucket are unchanged: the version IDs (null), contents, and permissions remain the same.
Enabling and suspending versioning is done at the bucket level. When you enable
versioning for a bucket, all objects added to it will have a unique version ID.
Unique version IDs are randomly generated, Unicode, UTF-8 encoded, URL-ready, opaque
strings that are at most 1024 bytes long. An example version ID is
3/L4kqtJlcpXroDTDmJ+rmSpXd3dIbrHY+MTRCxf3vjVBH40Nr8X8gdRQBpUMLUo. Only Amazon S3
generates version IDs. They cannot be edited.
For simplicity, we will use much shorter IDs in all our examples.
PUT an object in a version-enabled bucket, the old
version is not overwritten. The following figure shows that when a new version of
PUT into a bucket that
already contains an object with the same name, the original object (ID = 111111)
remains in the bucket, Amazon S3 generates a new version ID (121212), and adds the
newer version to the bucket.
This functionality prevents you from accidentally overwriting or deleting objects and affords you the opportunity to retrieve a previous version of an object.
DELETE an object, all versions remain in the bucket
and Amazon S3 inserts a delete marker, as shown in the following figure.
The delete marker becomes the latest version of the object. By default,
GET requests retrieve the most recently stored version. Performing a
GET Object request when the latest version is a delete
marker returns a
404 Not Found error, as shown in the following figure.
You can, however,
GET an older version of an object by
specifying its version ID. In the following figure, we
specific object version, 111111. Amazon S3 returns that object version even though
it's not the latest version.
You can permanently delete an object by specifying the version you want to delete.
Only the owner of an Amazon S3 bucket can permanently delete a version. The
following figure shows how
DELETE versionId permanently deletes
an object from a bucket and that Amazon S3 doesn't insert a delete marker.
You can add additional security by configuring a bucket to enable MFA (Multi-Factor Authentication) Delete. When you do, the bucket owner must include two forms of authentication in any request to delete a version or change the versioning state of the bucket. For more information, see MFA Delete.
For more information, see Using Versioning.