Programming Amazon Web Services

Objects

S3 objects are resources that store data. They are somewhat similar to the files in a standard computer system, but there are a number of important differences which were summarized in S3 Architecture.”

An object can contain up to 5 GB of data, or it can be entirely empty. An object can store two types of information: data and metadata. The data stored by an object is its main content, such as a photo or text document. In addition to the data content, an object can store metadata that provides further information about the object, such as when it was created and the type of data it contains. You can store your own metadata information when you create or replace an object.

Each object resource in S3 can have access control permissions applied to it, allowing you to keep the object private, or to make it available to other S3 users or the general public.

Object Keys and Hierarchical Naming

Each object in S3 is identified by a unique name, known as its key, which uniquely identifies it within a bucket. Object keys must not be longer than 1,024 bytes when encoded as UTF-8, and they can contain almost any characters, including spaces and punctuation. Objects are similar to files, so it makes sense to use obvious names for your objects, as you would for a file, such as My Birthday Cake.jpg.

One major difference between the S3 storage model and the average computer file system is that S3 has no notion of a hierarchical folder or directory structure. S3 buckets contain objects—that is ...