Uploading and downloading objects in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when you upload an object with the same key to an S3 bucket?

You upload a file named report.pdf to an Amazon S3 bucket. Later, you upload another file with the same name report.pdf to the same bucket. What is the result?

A The bucket creates a version of the file but keeps both accessible by default.

B The upload fails with an error because the key already exists.

C The new file overwrites the existing file with the same key.

D Both files are stored separately with different keys automatically.

💡 Hint

Think about how S3 handles object keys and overwriting.

In Amazon S3, object keys are unique within a bucket. Uploading an object with the same key replaces the existing object. Versioning must be enabled to keep multiple versions.

❓ Configuration

intermediate

Which AWS CLI command downloads an object from S3 to your local machine?

You want to download the file image.png from the S3 bucket my-bucket to your current local directory using AWS CLI. Which command is correct?

A aws s3 get-object my-bucket image.png ./

B aws s3 download s3://my-bucket/image.png ./

C aws s3 fetch s3://my-bucket/image.png ./

D aws s3 cp s3://my-bucket/image.png ./

💡 Hint

Look for the AWS CLI command that copies files between S3 and local.

The aws s3 cp command copies files between S3 and your local system. The other commands are invalid or do not exist.

❓ Architecture

advanced

How to design a secure upload system for user files to S3 with minimal permissions?

You want users to upload files directly to an S3 bucket without exposing your AWS credentials or giving full bucket access. Which approach is best?

A Generate pre-signed URLs for upload with limited time and permissions.

B Give users IAM user credentials with full S3 bucket access.

C Allow public write access on the S3 bucket so users can upload freely.

D Use AWS Lambda to upload files on behalf of users with admin permissions.

💡 Hint

Think about temporary, limited access for uploads without exposing credentials.

Pre-signed URLs allow users to upload files directly to S3 with limited permissions and expiration, improving security and reducing complexity.

❓ security

advanced

What is the effect of enabling S3 bucket versioning on object uploads and deletions?

You enable versioning on an S3 bucket. What happens when you upload a new object with the same key or delete an object?

A New uploads overwrite existing objects; deletions permanently remove the object.

B New uploads create new versions; deletions add a delete marker without removing versions.

C New uploads fail if the key exists; deletions are disabled.

D New uploads create copies with different keys; deletions archive the object.

💡 Hint

Consider how versioning preserves object history.

With versioning enabled, each upload creates a new version. Deleting an object adds a delete marker but does not remove previous versions, allowing recovery.

✅ Best Practice

expert

Which method optimizes large file uploads to S3 for reliability and performance?

You need to upload a 10 GB video file to S3. Which method is best to ensure efficient upload and recovery from failures?

A Use multipart upload to upload parts in parallel and retry failed parts.

B Upload the entire file in a single <code>put-object</code> request.

C Split the file manually and upload each part as a separate object.

D Compress the file and upload it using the AWS CLI <code>sync</code> command.

💡 Hint

Think about handling large files and network interruptions.

Multipart upload splits large files into parts uploaded in parallel. It allows retrying failed parts without restarting the entire upload, improving reliability and speed.

Practice

1. What does uploading an object to an AWS S3 bucket mean?

easy

A. Deleting a file from the cloud storage

B. Saving a file from your computer to the cloud storage

C. Copying a file from one folder to another on your computer

D. Viewing a file stored in the cloud without downloading

Solution

1. Step 1: Understand uploading concept

   Uploading means moving or saving a file from your local device to a remote place, like cloud storage.

2. Step 2: Apply to AWS S3 context

   In AWS S3, uploading an object means saving your local file into an S3 bucket in the cloud.

3. Final Answer:

   Saving a file from your computer to the cloud storage -> Option B

4. Quick Check:

   Uploading = Save local file to cloud [OK]

Hint: Uploading means sending files from your PC to cloud storage [OK]

Common Mistakes:

• Confusing uploading with downloading
• Thinking uploading deletes files
• Mixing local file moves with cloud uploads

2. Which AWS CLI command correctly uploads a file named photo.jpg to a bucket called mybucket?

easy

A. aws s3 get photo.jpg s3://mybucket/

B. aws s3 download photo.jpg s3://mybucket/

C. aws s3 cp photo.jpg s3://mybucket/

D. aws s3 remove photo.jpg s3://mybucket/

Solution

1. Step 1: Identify correct AWS CLI upload command

   The command to upload files to S3 is aws s3 cp followed by the local file and the bucket path.

2. Step 2: Match command with given file and bucket

   Using aws s3 cp photo.jpg s3://mybucket/ uploads the file photo.jpg to the bucket mybucket.

3. Final Answer:

   aws s3 cp photo.jpg s3://mybucket/ -> Option C

4. Quick Check:

   Upload command = aws s3 cp [OK]

Hint: Use 'aws s3 cp' to copy files to S3 bucket [OK]

Common Mistakes:

• Using 'download' instead of 'cp' for upload
• Confusing 'get' with upload command
• Using 'remove' which deletes files

3. What will be the result of this AWS CLI command?
aws s3 cp s3://mybucket/report.pdf ./

medium

A. Downloads report.pdf from the bucket to current folder

B. Uploads report.pdf from local to the bucket

C. Deletes report.pdf from the bucket

D. Lists all files in the bucket

Solution

1. Step 1: Understand the command structure

   The command aws s3 cp copies files. The source is s3://mybucket/report.pdf and destination is ./ (current folder).

2. Step 2: Determine direction of copy

   Since source is S3 and destination is local, the file is downloaded from the bucket to the local folder.

3. Final Answer:

   Downloads report.pdf from the bucket to current folder -> Option A

4. Quick Check:

   Source S3 to local = download [OK]

Hint: Source path starting with s3:// means download to local [OK]

Common Mistakes:

• Thinking 'cp' always uploads
• Confusing source and destination order
• Assuming it deletes files

4. You run this command to download a file but get an error:
aws s3 cp s3://mybucket/data.csv ./
What is the most likely cause?

medium

A. You forgot to add --recursive flag

B. You used the wrong command; should be aws s3 upload

C. The local folder ./ does not exist

D. The file data.csv does not exist in the bucket

Solution

1. Step 1: Analyze the error context

   The command is correct for downloading a single file. An error usually means the file is missing or inaccessible.

2. Step 2: Check common causes

   If the file data.csv is not in the bucket, the command fails. The local folder ./ always exists as current directory, and --recursive is not needed for single files.

3. Final Answer:

   The file data.csv does not exist in the bucket -> Option D

4. Quick Check:

   Missing file in bucket causes download error [OK]

Hint: Check if file exists in bucket before downloading [OK]

Common Mistakes:

• Using wrong command for download
• Assuming local folder missing causes error
• Adding unnecessary flags

5. You want to upload all files from your local folder photos/ to the S3 bucket mybucket preserving folder structure. Which command should you use?

hard

A. aws s3 sync photos/ s3://mybucket/

B. aws s3 cp photos/ s3://mybucket/

C. aws s3 cp photos/ s3://mybucket/ --no-recursive

D. aws s3 mv photos/ s3://mybucket/ --recursive

Solution

1. Step 1: Understand folder upload options

   To upload multiple files preserving folder structure, aws s3 sync is preferred as it copies all files and folders efficiently.

2. Step 2: Compare commands

   aws s3 cp --recursive can copy folders but sync is better for syncing changes and preserving structure. mv moves files (deletes local), which may not be desired.

3. Final Answer:

   aws s3 sync photos/ s3://mybucket/ -> Option A

4. Quick Check:

   Use 'sync' to upload folders preserving structure [OK]

Hint: Use 'aws s3 sync' for folder uploads preserving structure [OK]

Common Mistakes:

• Using 'cp' without --recursive for folders
• Using 'mv' which deletes local files
• Forgetting to preserve folder structure