Object Versioning

Object versioning in swift is implemented by setting a flag on the container to tell swift to version all objects in the container. The flag is the X-Versions-Location header on the container, and its value is the container where the versions are stored. It is recommended to use a different X-Versions-Location container for each container that is being versioned.

When data is PUT into a versioned container (a container with the versioning flag turned on), the existing data in the file is redirected to a new object and the data in the PUT request is saved as the data for the versioned object. The new object name (for the previous version) is <versions_container>/<length><object_name>/<timestamp>, where length is the 3-character zero-padded hexadecimal length of the <object_name> and <timestamp> is the timestamp of when the previous version was created.

A GET to a versioned object will return the current version of the object without having to do any request redirects or metadata lookups.

A POST to a versioned object will update the object metadata as normal, but will not create a new version of the object. In other words, new versions are only created when the content of the object changes.

A DELETE to a versioned object will only remove the current version of the object. If you have 5 total versions of the object, you must delete the object 5 times to completely remove the object.

How to Enable Object Versioning in a Swift Cluster

This middleware was written as an effort to refactor parts of the proxy server, so this functionality was already available in previous releases and every attempt was made to maintain backwards compatibility. To allow operators to perform a seamless upgrade, it is not required to add the middleware to the proxy pipeline and the flag allow_versions in the container server configuration files are still valid. In future releases, allow_versions will be deprecated in favor of adding this middleware to the pipeline to enable or disable the feature.

In case the middleware is added to the proxy pipeline, you must also set allow_versioned_writes to True in the middleware options to enable the information about this middleware to be returned in a /info request.

Upgrade considerations: If allow_versioned_writes is set in the filter configuration, you can leave the allow_versions flag in the container server configuration files untouched. If you decide to disable or remove the allow_versions flag, you must re-set any existing containers that had the ‘X-Versions-Location’ flag configured so that it can now be tracked by the versioned_writes middleware.

Examples Using curl

First, create a container with the X-Versions-Location header or add the header to an existing container. Also make sure the container referenced by the X-Versions-Location exists. In this example, the name of that container is “versions”:

curl -i -XPUT -H "X-Auth-Token: <token>" -H "X-Versions-Location: versions" http://<storage_url>/container
curl -i -XPUT -H "X-Auth-Token: <token>" http://<storage_url>/versions

Create an object (the first version):

curl -i -XPUT --data-binary 1 -H "X-Auth-Token: <token>" http://<storage_url>/container/myobject

Now create a new version of that object:

curl -i -XPUT --data-binary 2 -H "X-Auth-Token: <token>" http://<storage_url>/container/myobject

See a listing of the older versions of the object:

curl -i -H "X-Auth-Token: <token>" http://<storage_url>/versions?prefix=008myobject/

Now delete the current version of the object and see that the older version is gone:

curl -i -XDELETE -H "X-Auth-Token: <token>" http://<storage_url>/container/myobject
curl -i -H "X-Auth-Token: <token>" http://<storage_url>/versions?prefix=008myobject/

How to Disable Object Versioning in a Swift Cluster

If you want to disable all functionality, set allow_versioned_writes to False in the middleware options.

Disable versioning from a container (x is any value except empty):

curl -i -XPOST -H "X-Auth-Token: <token>" -H "X-Remove-Versions-Location: x" http://<storage_url>/container