AWS Simple Storage Service S3

Some of the key notes related to S3 from AWS documentation

Amazon S3 has a simple web services interface that can be used to store and retrieve any amount of data, at any time, from anywhere on the web.

Amazon S3 Data Consistency Model

Amazon S3 provides read-after-write consistency for PUTS of new objects in your S3 bucket in all Regions with one caveat. The caveat is that if you make a HEAD or GET request to the key name (to find if the object exists) before creating the object, Amazon S3 provides eventual consistency for read-after-write.

Amazon S3 offers eventual consistency for overwrite PUTS and DELETES in all Regions.

Updates to a single key are atomic. For example, if you PUT to an existing key, a subsequent read might return the old data or the updated data, but it never returns corrupted or partial data.

Amazon S3 achieves high availability by replicating data across multiple servers within AWS data centers. If a PUT request is successful, your data is safely stored. However, information about the changes must replicate across Amazon S3, which can take some time, and so you might observe the following behaviors:

• A process writes a new object to Amazon S3 and immediately lists keys within its bucket. Until the change is fully propagated, the object might not appear in the list.
• A process replaces an existing object and immediately tries to read it. Until the change is fully propagated, Amazon S3 might return the previous data.
• A process deletes an existing object and immediately tries to read it. Until the deletion is fully propagated, Amazon S3 might return the deleted data.
• A process deletes an existing object and immediately lists keys within its bucket. Until the deletion is fully propagated, Amazon S3 might list the deleted object.

Note

• Amazon S3 does not currently support object locking. If two PUT requests are simultaneously made to the same key, the request with the latest timestamp wins. If this is an issue, you will need to build an object-locking mechanism into your application.
• Updates are key-based. There is no way to make atomic updates across keys. For example, you cannot make the update of one key dependent on the update of another key unless you design this functionality into your application.

Storage Classes

Amazon S3 offers a range of storage classes designed for different use cases. These include

1. Amazon S3 STANDARD for general-purpose storage of frequently accessed data, 
2. Amazon S3 STANDARD_IA for long-lived, but less frequently accessed data, and 
3. GLACIER for long-term archive.

Operations

Following are the most common operations that you'll execute through the API.

1. Create a bucket – Create and name your own bucket in which to store your objects.
2. Write an object – Store data by creating or overwriting an object. When you write an object, you specify a unique key in the namespace of your bucket. This is also a good time to specify any access control you want on the object.
3. Read an object – Read data back. You can download the data via HTTP or BitTorrent.
4. Delete an object – Delete some of your data.
5. List keys – List the keys contained in one of your buckets. You can filter the key list based on a prefix.