S3 Exam Tips

Basics

Remember that S3 is object-based i.e. allows you to upload files. Object-based storage only (for files).
Not suitable to install an OS or run a database.
Files can be from 0 Bytes to 5 TB.
The largest size file you can transfer to S3 using a PUT is 5 GB.
There is unlimited storage
Files are stored in Buckets
S3 is a universal namespace. That is, names must be unique globally.
https://s3-us-west-1.amazonaws.com/acloudguru
Read after write consistency for PUTS of new objects
Eventual Consistency for overwrite PUTS and DELETEs (can take some time to propagate).
S3 (durable, immediately available, frequently accessed)
S3 IA (durable, immediately available, infrequently accessed)
S3 One-Zone IA: Same as IA. However, data is stored in a single AZ only.
S3 Reduced Redundancy Storage (data that is easily reproducible, such as thumbnails, etc.)
Glacier: Archived data, where you can wait 3-5 hours before accessing.
Remember the core fundamentals of an S3 object
- Key (name0)
- Value (data)
- Version ID
- Metadata
- Subresources - bucket-specific configuration.
  - Bucket policies, Access Control Lists
  - Cross-Origin Resource Sharing (CORS)
  - Transfer Acceleration
Successful uploads will generate an HTTP 200 status code when you use the CLI or API.
Make sure you read the S3 FAQ. GOOD TO READ JUST BEFORE EXAM
AWS Storage Gateway acts as a file system mounted on an S3 bucket.

By default, all newly created buckets are Private.
You can setup access control to your buckets using:
- Bucket Policies: Applied at a bucket level.
- Access Control Lists: Applied at an object level.
S3 Buckets can be configured to create access logs, which log all requests made to the S3 bucket. These logs can be written to another bucket.

Encryption In-Transit
- SSL/TLS (HTTPS)
Encryption At Rest
- Server-Side Encryption
  - SSE-S3
  - SSE-KMS
  - SSE-C (Customer-Managed)
- Client-Side Encryption
If you want to enforce the use of encryption for your files stored in S3, use an S3 Bucket Policy to deny all PUT requests that don't include the x-amz-server-side-encryption parameter in the request header.

Used to enable cross-origin access for your AWS resources. E.g. S3-hosted website accessing JavaScript or image files located in another S3 bucket.
By default, resources in one bucket cannot access resources located in another.
To allow cross-origin access, we need to configure CORS on the bucket being accessed and enable access for the origin (bucket) attempting to access.
Always use the S3 website URL, not the regular bucket URL:
- http://acloudguru.s3-website.eu-west-1.amazonaws.com

Edge Location: This is the location where content will be cached. This is separate to an AWS Region/AZ.
Origin: This is the origin of all the files that the CDN will distribute. Origins can be an S3 Bucket, an EC2 instance, an ELB, or Route53.
Distribution: This is the name given to the CDN, which consists of Edge Locations.
- Web Distribution: Typically used for websites.
- RTMP: Used for media streaming
Edge Locations are not just READ only. You can write to them too. (i.e. PUT an object onto them).
CloudFront Edge Locations are utilized by S3 Transfer Acceleration to reduce latency for S3 uploads.
Objects are cached for the life of the TTL (Time To Live)
You can clear cached objects, but you will be charged for invalidations.

Remember the 2 main approaches to Performance Optimization for S3:
- GET-Intensive Workloads: Use CloudFront
- Mixed Workloads (DEPRECATED JULY 2018): Avoid sequential key names for your S3 objects. Instead, add a random prefix like a hex hash to the key name to prevent multiple objects from being stored on the same partition.

Again, read the S3 FAQS.