Immutable Audit Logs in AWS S3 with Read‑Only Access

The request came from security: make the audit logs impossible to alter, even by accident. No hidden write access. No quiet delete.

Immutable audit logs in AWS S3 start with one non‑negotiable step—S3 Object Lock. This setting fixes each log object in place. You choose retention in days or years, and AWS enforces it. Attempting to overwrite or delete within the lock window fails. This is the backbone for compliance, incident response, and proving your data integrity.

The next layer is access control. Use IAM to define read‑only roles for S3. Grant only s3:GetObject and list permissions. Remove s3:DeleteObject, s3:PutObject, and all modify actions. Attach the role to the principals servicing audit reads, not writes. Combine this with versioning to ensure any object change is tracked and preserved.

For logging itself, target a dedicated bucket. Enable server‑side encryption with AWS KMS. Configure your applications or AWS CloudTrail to write directly into this bucket under a write‑only service role. Readers—human or automated—must authenticate with the read‑only role. This separation of duties eliminates cross‑access that can break immutability.

Monitoring completes the loop. Use AWS CloudWatch to alert on denied write attempts. Set S3 bucket logging or AWS Config to detect policy drift. Immutable logs are only as strong as the controls you keep watching.

With immutable audit logs in AWS S3, backed by read‑only IAM roles, you lock down history. You get evidence that survives tampering. You get truth—stored, versioned, encrypted, and protected by policy.

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