What Is Amazon S3? Object Storage for the Cloud

Amazon S3 (Simple Storage Service) is AWS object store: you put files (objects) into buckets and read them back over HTTP, with extreme durability and effectively unlimited scale.

S3 is one of the oldest and most-used AWS services. Instead of a filesystem with directories, it stores objects in flat buckets, each addressed by a key. It is designed for very high durability and is the default home for backups, static assets, data lakes, and build artifacts.

Buckets, objects, and keys

A bucket is a globally named container; an object is a file plus metadata; a key is the object name within the bucket. There are no real folders, but slashes in keys create a folder-like view. Each object can be up to several terabytes.

Durability and storage classes

Standard for frequently accessed data.
Infrequent Access for data you rarely read but keep.
Glacier tiers for cheap long-term archival.
Lifecycle rules that move objects between tiers automatically.

Access control

By default buckets are private. You grant access with IAM policies, bucket policies, and presigned URLs for temporary direct access. Public hosting requires explicit configuration, which is why accidental public buckets make headlines.

Serving static websites

S3 can host a static site directly, and is usually paired with CloudFront for a CDN, HTTPS, and caching at the edge. This combination is a common, cheap way to deploy front-end builds.

Role in CI/CD

Pipelines use S3 constantly: storing build artifacts and test reports, caching dependencies, and deploying static sites by syncing a build folder to a bucket. A deploy job runs aws s3 sync and then invalidates the CloudFront cache, all authenticated through an IAM/OIDC role rather than long-lived keys.

Key takeaways

S3 stores objects in buckets, addressed by keys, with very high durability.
Storage classes and lifecycle rules optimize cost for hot vs cold data.
Pipelines use S3 for artifacts and to deploy static sites, often fronted by CloudFront.