# Basic Concepts

#### Basic Concepts Related to OBS APIs

- Domain

  You can register a domain with the cloud service. The domain has full access permissions for all the resources and cloud services that are subscribed under it. The domain can also reset user passwords and grant permissions to users. A domain is a payment entity. To keep the domain secure, it is recommended that you create users under the domain to perform routine management operations.

- User

  You can create users under a domain on Identity and Access Management (IAM), and authorize the users with permissions required for accessing cloud services. Each IAM user has its own identity credentials (password and access keys).

  On the My Credentials page on the console, you can view the domain ID and user ID, you can also manage the access keys of the domain and IAM users.

  Access keys of the domain and its IAM users are required for authentication when calling APIs.

- Bucket

  A bucket is a container where objects are stored. It is the top namespace in OBS. Each object must reside in a bucket. For example, if the object named picture.jpg is stored in the photo bucket, you can use the following URL to access the object: http://photo.obs.region.example.com/picture.jpg.

- Objects

  An object is a basic data unit on OBS. A bucket can store multiple objects, and OBS does not distinguish between object types. Objects are serialized in OBS. An object may be a text, a video, or any other types of files. In OBS, the size of a file can range from 0 bytes to 48.8 TB. However, when an object is uploaded through the PutObject operation, it cannot exceed the maximum size of 5 GB. Use the multipart upload method, if the object size is larger than 5 GB.

- Region

  A region is a geographic area in which cloud resources are deployed. Availability zones (AZs) in the same region can communicate with each other over an intranet, while AZs in different regions are isolated from each other. Deploying cloud resources in different regions can better suit certain user requirements or comply with local laws or regulations.

  Each bucket in OBS must reside in a region. You can specify the region when creating the bucket. Once a bucket is created, its region cannot be changed. Select the most appropriate region for a bucket based on the location, cost, and regulatory compliance requirements. For details about regions, see Endpoints.

Parent topic: Before You Start