Friday 13 May 2022

AWS Simple Storage Service (S3)

AWS S3 is an infinitely scalable storage solution which provides high data availability which is achieved by storing data across multiple servers, at multiple locations.
S3 is used for storing any kind of data, in its native format.

Data objects are stored within S3 buckets which are like containers for grouping stored objects. We can create as many buckets as we need. Everything inside S3 bucket is an object: flat files (text, binary, images, videos etc...) and folders.

Max allowed file size is 5 TB.

How to create a S3 bucket

One way is to use AWS Management Console. We need to choose a name and region.

S3 bucket name must be unique because AWS creates DNS name for each new bucket. It comes in form:


DNS name is publicly accessible. Name also needs to be DNS-compliant: no upper cases and underscores, between 3 and 63 characters long, and should not end with a dash character. 

Objects are accessed via urls like:


Every object in S3 bucket has:
  • data
    • Key - actual name of the object e.g. my-file.txt
    • Value - actual data
  • metadata
    • Owner
    • Size
    • Last Modified
By default, upon creating a bucket and uploading the objects, no one can access them apart from bucket owner. Access is controlled via bucket policies and access control lists. Bucket policies are at bucket level and access control lists are at the level of individual objects. 

Just like IAM policies, bucket policies are JSON documents. With them we can grant access to users, groups, users from other AWS accounts or public access.

Example: bucket policy which allows user adam to retrieve all objects in a bucket

    "Version": "2022-05-13",
    "Statement": [
            "Action": [
                "s3: GetObject"
            "Effect": "Allow",
            "Resource": "arn:aws:s3:::my-bucket/*",
            "Principal": {
                "AWS": [


No comments: