Interview Q&A / AWS & Cloud

1. What is Amazon S3 and what are its storage classes?

   S3 is AWS's object storage. You store files as objects inside buckets and access them by key over HTTPS. Storage classes trade storage cost against access speed and retrieval cost, from S3 Standard for frequently used data to the Glacier classes for archives you rarely read.

   BeginnerIn-depth4 min read
2. What are S3 lifecycle rules and what can they do?

   Lifecycle rules automatically move objects to cheaper storage classes after a set number of days, or delete them. They also clean up old versions and incomplete multipart uploads.

   BeginnerQuick answer1 min read
3. What is the difference between S3 Standard-IA and S3 One Zone-IA?

   Both are for data accessed rarely but needed quickly. Standard-IA stores copies across at least three Availability Zones. One Zone-IA keeps data in a single AZ at lower cost, so it is lost if that AZ is destroyed.

   BeginnerQuick answer1 min read
4. How would you give a user read-only access to one specific S3 bucket?

   Attach an identity policy that allows s3:ListBucket on the bucket ARN and s3:GetObject on the objects inside it using the bucket ARN with /*. Nothing else is allowed, so the user can read but not write or delete.

   IntermediateQuick answer1 min read
5. Is Amazon S3 eventually consistent or strongly consistent?

   S3 gives strong read-after-write consistency for all object operations. After a successful PUT, overwrite or DELETE, any later GET or LIST immediately reflects the change.

   IntermediateQuick answer1 min read
6. What are the S3 Glacier storage classes and how do their retrieval times differ?

   Glacier Instant Retrieval returns data in milliseconds. Glacier Flexible Retrieval takes minutes to hours depending on the option. Glacier Deep Archive is the cheapest and takes hours, typically around 12 hours or more.

   IntermediateQuick answer1 min read
7. What happens when you delete an object in an S3 bucket that has versioning enabled?

   S3 does not remove the data. It adds a delete marker as the newest version, so normal reads return 404, but older versions remain and can be restored by removing the marker or fetching a version ID.

   IntermediateQuick answer1 min read
8. What is an S3 presigned URL and when would you use it?

   A presigned URL is a temporary link, signed with someone's credentials, that lets a person upload or download one specific S3 object without having AWS credentials. It stops working when it expires.

   IntermediateQuick answer1 min read