Amazon S3 for Developers
Difficulty: medium
Overview
Consistency: Strong read-after-write consistency for all operations since Dec 2020.
Multipart Upload: Recommended > 100 MB, required > 5 GB. Upload parts in parallel. Parts can be retried. Must complete or abort.
Pre-signed URLs: Temp access for GET or PUT. Up to 7 days (IAM user) or 12 hours (IAM role via STS).
S3 Event Notifications: ObjectCreated, ObjectRemoved → SQS, SNS, Lambda, EventBridge.
Object Lock (WORM):
- Compliance Mode: No one can delete before retention expires.
- Governance Mode: Privileged users can override.
SSE Options:
- SSE-S3: AWS manages keys. Header: x-amz-server-side-encryption: AES256.
- SSE-KMS: KMS manages keys. Uses GenerateDataKey per object.
- SSE-C: Customer provides key per request. HTTPS required.
Versioning: DELETE creates delete marker. MFA Delete: requires MFA to permanently delete versions.
CORS: Configure on bucket for browser clients making direct S3 requests from different domains.
S3 Select: Query data in-place with SQL. Reduce data transfer.
Transfer Acceleration: CloudFront edge for upload acceleration. URL: bucket.s3-accelerate.amazonaws.com.
Practice Linked Questions
Q1. A developer needs to allow a web browser to make cross-origin requests to an S3 bucket to display images. The browser shows a CORS error. What must the developer configure?
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Q2. A developer uses the S3 SDK to upload 100 MB files. Uploads frequently fail on slow connections. What S3 feature should the developer use to improve reliability?
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Q3. A developer needs to generate a temporary URL allowing an unauthenticated user to download a specific S3 object for exactly 15 minutes. Which S3 feature should be used?
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Q4. A developer accidentally deleted 1,000 S3 objects. The bucket does not have versioning enabled. Can the objects be recovered?
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Q5. A developer needs to store sensitive medical records in S3. The data must be encrypted with a customer-managed key, and all key usage must be auditable. The developer also needs to rotate the key annually. Which S3 encryption configuration satisfies all requirements?
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Q6. A developer needs to trigger a Lambda function every time a new object is uploaded to an S3 bucket. Which S3 feature should be configured?
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