* Add AWS Backup with offsite vault (audit C-7)
The account had zero AWS Backup vaults/plans, so 22 of 23 data stores
had no immutable, cross-region recovery path (audit finding C-7). One
ransomware event or rogue delete would erase primary plus same-region
snapshots/PITR.
Phase 1 ("critical data first") protects the seven highest-risk stores
with no offsite leg today (2 RDS, 2 DynamoDB, 3 S3) via a daily plan in
a new us-east-1 vault, copied cross-region into a governance-locked
us-west-2 vault. Governance (not compliance) mode first so the plan can
be validated before committing to irreversible immutability.
The backup service role is backup-only (no restore policies) to stay
least-privilege; restores get a separate audited path later. Resources
are selected by explicit ARN to avoid drifting the stacks that own them.
Deploys via the shared cdk deploy --all alongside the C-1 CloudTrail
stack. See the README pre-deploy gates (S3 versioning, database-1
unencrypted copy smoke-test, DynamoDB PITR) before the first run.
* Grant AWS Backup service use of vault CMKs
The L2 BackupVault does not grant the backup service principal use of a
customer-managed key; the synthesized key policy only delegated to
account IAM. Cross-region copy of encrypted RDS/EBS recovery points uses
KMS grants on the destination key, so without an explicit grant those
copy jobs fail — and silently, since the account has no CloudTrail yet.
Add backup.amazonaws.com crypto + CreateGrant statements to both vault
keys, scoped by aws:SourceAccount (cross-review BLOCK 2; mirrors the
discipline used on the C-1 CloudTrail key). Same class of bug the C-1
cross-review caught on the CloudTrail CMK.
