Object Storage API overview

OpenStack Object Storage is a highly available, distributed, eventually consistent object/blob store. You create, modify, and get objects and metadata by using the Object Storage API, which is implemented as a set of Representational State Transfer (REST) web services.

For an introduction to OpenStack Object Storage, see the OpenStack Swift Administrator Guide.

You use the HTTPS (SSL) protocol to interact with Object Storage, and you use standard HTTP calls to perform API operations. You can also use language-specific APIs, which use the RESTful API, that make it easier for you to integrate into your applications.

To assert your right to access and change data in an account, you identify yourself to Object Storage by using an authentication token. To get a token, you present your credentials to an authentication service. The authentication service returns a token and the URL for the account. Depending on which authentication service that you use, the URL for the account appears in:

  • OpenStack Identity Service. The URL is defined in the service catalog.

  • Tempauth. The URL is provided in the X-Storage-Url response header.

In both cases, the URL is the full URL and includes the account resource.

The Object Storage API supports the standard, non-serialized response format, which is the default, and both JSON and XML serialized response formats.

The Object Storage system organizes data in a hierarchy, as follows:

  • Account. Represents the top-level of the hierarchy.

    Your service provider creates your account and you own all resources in that account. The account defines a namespace for containers. A container might have the same name in two different accounts.

    In the OpenStack environment, account is synonymous with a project or tenant.

  • Container. Defines a namespace for objects. An object with the same name in two different containers represents two different objects. You can create any number of containers within an account.

    In addition to containing objects, you can also use the container to control access to objects by using an access control list (ACL). You cannot store an ACL with individual objects.

    In addition, you configure and control many other features, such as object versioning, at the container level.

    You can bulk-delete up to 10,000 containers in a single request.

    You can set a storage policy on a container with predefined names and definitions from your cloud provider.

  • Object. Stores data content, such as documents, images, and so on. You can also store custom metadata with an object.

    With the Object Storage API, you can:

    • Store an unlimited number of objects. Each object can be as large as 5 GB, which is the default. You can configure the maximum object size.

    • Upload and store objects of any size with large object creation.

    • Use cross-origin resource sharing to manage object security.

    • Compress files using content-encoding metadata.

    • Override browser behavior for an object using content-disposition metadata.

    • Schedule objects for deletion.

    • Bulk-delete up to 10,000 objects in a single request.

    • Auto-extract archive files.

    • Generate a URL that provides time-limited GET access to an object.

    • Upload objects directly to the Object Storage system from a browser by using form POST middleware.

    • Create symbolic links to other objects.

The account, container, and object hierarchy affects the way you interact with the Object Storage API.

Specifically, the resource path reflects this structure and has this format:


For example, for the flowers/rose.jpg object in the images container in the 12345678912345 account, the resource path is:


Notice that the object name contains the / character. This slash does not indicate that Object Storage has a sub-hierarchy called flowers because containers do not store objects in actual sub-folders. However, the inclusion of / or a similar convention inside object names enables you to create pseudo-hierarchical folders and directories.

For example, if the endpoint for Object Storage is objects.mycloud.com, the returned URL is https://objects.mycloud.com/v1/12345678912345.

To access a container, append the container name to the resource path.

To access an object, append the container and the object name to the path.

If you have a large number of containers or objects, you can use query parameters to page through large lists of containers or objects. Use the marker, limit, and end_marker query parameters to control how many items are returned in a list and where the list starts or ends. If you want to page through in reverse order, you can use the query parameter reverse, noting that your marker and end_markers should be switched when applied to a reverse listing. I.e, for a list of objects [a, b, c, d, e] the non-reversed could be:


However, when reversed marker and end_marker are applied to a reversed list:


Object Storage HTTP requests have the following default constraints. Your service provider might use different default values.


Maximum value


Number of HTTP headers


Length of HTTP headers

4096 bytes

Length per HTTP request line

8192 bytes

Length of HTTP request

5 GB

Length of container names

256 bytes

Cannot contain the / character.

Length of object names

1024 bytes

By default, there are no character restrictions.

You must UTF-8-encode and then URL-encode container and object names before you call the API binding. If you use an API binding that performs the URL-encoding for you, do not URL-encode the names before you call the API binding. Otherwise, you double-encode these names. Check the length restrictions against the URL-encoded string.

The API Reference describes the operations that you can perform with the Object Storage API:

  • Storage accounts: Use to perform account-level tasks.

    Lists containers for a specified account. Creates, updates, and deletes account metadata. Shows account metadata.

  • Storage containers: Use to perform container-level tasks.

    Lists objects in a specified container. Creates, shows details for, and deletes containers. Creates, updates, shows, and deletes container metadata.

  • Storage objects: Use to perform object-level tasks.

    Creates, replaces, shows details for, and deletes objects. Copies objects with another object with a new or different name. Updates object metadata.