S3 General

  • Object-based storage — some might call it blob, can be any bytes, immutable once created.
  • Durability by duplication across the network
  • 0–5TB file limit
  • No limit on storage per account
  • Buckets are flat, unique in name across all AWS
  • Buckets can be accessed via URL
  • Uploading to S3 returns a 200


  • Designed for 99.99% availability
  • Guarantee 99.9% availability
  • Guarantee 99.999999999% durability

S3 Behaviours

  • S3 gives you read after write consistency, creating new content means you get that back right away
  • S3 gives you eventual consistency from updating existing objects. This is because of the duplication. It takes time to propagate.
  • There are some different storage classes, some include Infrequent Access and Glacier. The trade-offs are availability and minimum storage duration and cost.
  • Objects are key-value storage with metadata and custom data. Version ID’s if you enable versioning and an ACL (access control list).

S3 Versioning

  • Versioning can be turned on but only suspended once on.
  • Versioning a bucket means a delete is a ‘delete marker’

Life Cycle Management

  • Life Cycle Management is setting up transitions for objects to move objects into IA Access etc.
  • Life Cycle has an expiry (delete) transition too.

S3 Cross-Region

  • Copies objects from one bucket to another in different regions
  • Requires versioning turned on
  • Does not replicate retrospectively so decide upfront if you need it probably.
  • Used to place the assets closer to the user.
  • Delete markers are replicated, but deleting the delete markers does not replicate… (circa 2018 — need to verify this myself still)

S3 => Cloudfront

  • Used to reduce the object retrieval time
  • Origin — location of the objects the CDN will distribute, can be S3, could be a load balancer, EC2, server etc etc
  • Edge Location — AWS server where the object will be cached
  • Distribution — A CDN configuration of edge locations used for a particular CloudFront e.g. Web HTTP/S
  • Edge locations can accept uploads
  • TTL is the cache time
  • Caches can be invalidated to force the requester to go to the origin

S3 Security

  • All buckets are born Private
  • Buckets access can be done in the bucket itself on a per bucket basis
  • Access Control Lists let you control policy for a user in a more bucket instance agnostic way e.g. Read from Buckets, Write to Buckets
  • Objects can be controlled at the ACL level.
  • You can log bucket activity (into a separate bucket)
  • You can set up events when bucket activities are performed e.g. add a new item

S3 Security / Encryption

  • In transit, the objects are protected by SSL/TLS
  • At rest, there are some encryption options you can enable
  • SSE-S3 has its own built-in management
  • SSE-KMS (Key management store) another service can be used to protect and manage your own keys
  • SSE-C (Custom) lets you set your own keys and basically roll your own encryption.

S3 Transfer Acceleration

  • Lets you transfer data faster (lower latency)
  • Uses AWS’s own infrastructure
  • Costs x2.. not always worth it, so check.

S3 Static Website

  • Host an entire website
  • Requires no virtual website
  • Scales automatically




Fullish-stack engineer (codebykev.dev) and Lead front-end engineer @Cinch with 20 developing stuff for things with screens since the turn of the millenium.

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Kevin Jones

Kevin Jones

Fullish-stack engineer (codebykev.dev) and Lead front-end engineer @Cinch with 20 developing stuff for things with screens since the turn of the millenium.

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