title: “Amazon S3 Fundamentals” created: 2026-07-20 updated: 2026-07-20 type: knowledge tags:

aws
s3
storage
certification

Amazon S3 Fundamentals

What It Is

Amazon Simple Storage Service (Amazon S3) is an object storage service — not block storage (EBS) or file storage (EFS). It stores data as objects within buckets.

Object = file + metadata + unique key
Bucket = container for objects (flat namespace, no real folders — prefixes simulate hierarchy)

S3 is one of the most foundational AWS services. It appears in nearly every certification exam and real-world architecture. Use cases span websites, mobile apps, backup/restore, archive, enterprise apps, IoT, and big data analytics.

Key Concepts

Concept	Detail
Durability	99.999999999% (11 nines) — data is replicated across multiple AZs
Availability	Varies by storage class (99.99% for Standard)
Storage model	Object storage (not hierarchical file system)
Global namespace	Bucket names are globally unique across all AWS accounts
Max object size	5 TB (single PUT limited to 5 GB; use multipart for larger)
Region-bound	Objects stay in a region unless explicitly transferred

How It Works

You create a bucket in a specific AWS Region
You upload objects (files) into the bucket
Each object gets a unique key (its full path within the bucket)
Access is controlled via IAM policies, bucket policies, ACLs, and Block Public Access
Objects are accessed via HTTPS URLs: https://<bucket>.s3.<region>.amazonaws.com/<key>

Examples

Static website hosting
Data lake for analytics
Backup and disaster recovery
Log storage (CloudTrail, ELB, CloudFront)
Application data storage (reports pushed from EC2)

Gotchas

Bucket names are globally unique and immutable once created
S3 is eventually consistent for overwrite PUTs and DELETEs (though strong consistency was added in Dec 2020 for all operations)
Objects are private by default — you must explicitly grant access
Block Public Access (BPA) overrides any permissive ACL or policy

AWS Certification Notes