Stop 05 · Storage ServicesTopics · 1/9

Object Storage (S3, Cloud Storage, Blob Storage)

In short

Profile photos, PDF notes, backups, website images, huge data lakes: most of the world's cloud data sits in object storage. It's cheap, nearly bottomless, and the first service most people actually use.

Storing files as objects (not a traditional file system) with virtually unlimited scale — the default choice for static assets, backups, and data lakes across every major cloud provider.

The blob character hands a suitcase over a cloakroom counter and gets a token.

Think of it like this

The railway cloakroom

You hand your bag over at the station cloakroom and get a token. You don't care which shelf it's on. Show the token later and the bag comes back. Object storage is a giant cloakroom: give it a file, get a key, fetch it by key.

Watch it happen

Store and fetch by key

Your app

S3 bucket

PUT notes/os/unit1.pdf

1/5You upload a file with a key. The slashes just look like folders; the key is one long name.

The big ideas

What you need to know

Buckets, keys, objects

A bucket is the container, a key is the object's full name, and the object is the data plus metadata.

Practically unlimited

No disk to resize. Store one file or billions; you pay per gigabyte stored and per request.

Reached over HTTPS

Objects are read and written through an API, not mounted as a drive. Any app or CLI can use them.

Very durable

Data is copied across multiple zones automatically. Losing a file to hardware failure is extremely unlikely.

See it in code

Walk through the code

bash

1aws s3 mb s3://riya-notes-20262aws s3 cp unit1.pdf s3://riya-notes-2026/os/unit1.pdf3aws s3 ls s3://riya-notes-2026/os/4 5# Share for 1 hour without making the bucket public6aws s3 presign s3://riya-notes-2026/os/unit1.pdf --expires-in 3600

1/2Make a bucket, upload a file under a key, list keys with that prefix.

A presigned URL gives time-limited access to one object. It's the safe way to share without opening the bucket.

Save yourself the pain

Common mistakes

Oops

Making a bucket public so one friend can download a file.

Do this instead

Use a presigned URL. Public buckets get scanned by bots and are a classic source of leaks.

Oops

Treating object storage like a hard disk for a database.

Do this instead

Objects are written whole and read over HTTP. Databases need block storage attached to a server.

Your mission

Your personal notes bucket

~20 min

Quick check

In S3, what is 'photos/2026/trip.jpg'?

Go deeper

1Create a storage bucket and practice uploading, downloading, and deleting objects.
2Learn how object storage differs conceptually from a traditional file system.
3Configure basic access permissions on a bucket and understand the risk of accidental public exposure.