Staff SRE / Principal Architect [L3] AWS Cost & Architecture Staff SRE Scenario [L3]

Q: A team in AWS Account A is writing data to an S3 bucket in Account B. Account B explicitly grants them `s3:PutObject` in the bucket policy. However, when Account B administrators try to read the files, they get `Access Denied`. Why, and how is it fixed?

\"When an interviewer asks how I troubleshoot this in AWS, I frame it through my hands-on production experience. The interviewer is testing: Cross-account S3 Object Ownership.. I structure my answer around systematic triage first, root cause analysis second, and permanent remediation third.\" Key Strategy: Pro-Tip: Historically, in S3, the AWS account that uploads the object retains explicit ownership and full control of that object, even if t.

Historically, in S3, the AWS account that uploads the object retains explicit ownership and full control of that object, even if the buck...

#AWS #Cost & Architecture #L3 #Cloud #Infrastructure #S3

🎙️ Candidate Opening & Architectural Context

""When an interviewer asks how I troubleshoot this in AWS, I frame it through my hands-on production experience. The interviewer is testing: Cross-account S3 Object Ownership.. I structure my answer around systematic triage first, root cause analysis second, and permanent remediation third.""

🛠️ Production Runbook & Step-by-Step Resolution

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Production Solution & Architecture

Historically, in S3, the AWS account that uploads the object retains explicit ownership and full control of that object, even if the bucket itself belongs to a different account. Because Account A uploaded the file, Account A owns it, and Account B (the bucket owner) is locked out unless Account A explicitly grants them read ACLs during the upload (--acl bucket-owner-full-control). *The Modern Fix:* In Account B, go to the S3 bucket settings and enable S3 Object Ownership: Bucket owner enforced. This entirely disables all legacy ACLs. The bucket owner (Account B) automatically and forcefully assumes ownership of every file uploaded to the bucket, instantly restoring their read access.

💡 The Senior SRE Gold Nugget (Key Architectural Takeaway)

"Pro-Tip: Historically, in S3, the AWS account that uploads the object retains explicit ownership and full control of that object, even if t."

⚡ 60-Second Elevator Pitch Talking Points

Immediate Triage: Historically, in S3, the AWS account that uploads the object retains explicit ownership and ful
Run targeted verification commands before modifying configuration.
Automate permanent guardrails (CI check, alerts, IaC policy) to prevent recurrence.

Q: A team in AWS Account A is writing data to an S3 bucket in Account B. Account B explicitly grants them `s3:PutObject` in the bucket policy. However, when Account B administrators try to read the files, they get `Access Denied`. Why, and how is it fixed?

🛠️ Production Runbook & Step-by-Step Resolution

Production Solution & Architecture

📚 Related Production Scenarios in AWS