Architecting for Data Sovereignty: Designing EU-Only Storage on AWS European Sovereign Cloud

Stop guessing where data lives — build it inside the EU boundary

Pain point: You need storage that is physically and logically isolated inside the EU so contracts, auditors and regulators stop asking whether data ever crossed a border. This blueprint gives architects and developers a concrete, deployable design for storage, network and IAM inside the AWS European Sovereign Cloud (announced Jan 2026).

Executive summary — what this blueprint delivers

In 10 minutes you’ll get the core decisions and configuration patterns to ensure EU-only data residency on the AWS European Sovereign Cloud. The guide covers:

• Organizational controls (AWS Organizations, SCPs, Control Tower)
• VPC and network topology for in‑region isolation and EU-only egress
• Storage patterns for S3, EBS, EFS/FSx and archival (encryption, replication, Object Lock)
• IAM and KMS controls (CMKs, CloudHSM / BYOK, regional STS)
• Logging, auditing and continuous compliance inside the sovereign boundary
• Migration checklist, performance considerations and advanced mitigations

Why this matters in 2026

Late 2025 and early 2026 saw accelerated policy and product moves aimed at European digital sovereignty. AWS’s January 2026 launch of the AWS European Sovereign Cloud introduced an AWS region that is both physically and logically separate from other AWS regions.

Regulators and large enterprise customers now expect provable remedies: contractual assurances, in-region cryptographic controls, and technical evidence that metadata, logs and backups never left the EU. Architects must therefore combine cloud provider assurances with enforceable, verifiable controls.

Architectural principles — the rules to follow

• Region-first isolation: All sensitive workloads and storage must run in the European Sovereign Cloud region(s).
• Defense-in-depth: Network, IAM, encryption, and policy controls layered to reduce human or config mistakes.
• Least privilege + policy enforcement: Enforce guardrails at the organization level (SCPs) rather than relying on individual teams.
• Immutable audit trail: All policy and data actions logged and stored in-region with tamper protection.
• Zero trust for cross-border interactions: Explicit allow list and application-level protections for any external data flows.

1) Organizational controls: accounts, OUs and SCPs

Start at the top. Use AWS Organizations to create a dedicated Organizational Unit (OU) for EU‑sovereign workloads and enroll accounts into that OU. Use AWS Control Tower or a custom landing zone to provision baseline accounts.

Key step: attach Service Control Policies (SCPs) that prevent creation or usage of resources outside the sovereign region and disable global-only services that could leak data.

Example SCP: deny non-EU regions

{
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Deny",
    "Action": "*",
    "Resource": "*",
    "Condition": {
      "StringNotEquals": {"aws:RequestedRegion": ["eu-sovereign-1", "eu-sovereign-2"]}
    }
  }]
}

Replace region identifiers with the exact region names AWS publishes for the European Sovereign Cloud. Test SCPs in deny-mode using a non-production OU before broad rollout.

2) VPC and network design — keep traffic inside the boundary

Design a network that ensures in-region traffic stays in-region and that cross-border egress requires explicit, auditable approval.

Core network patterns

• Per-workload VPCs: One VPC per trust boundary (e.g., payments, PII analytics). Use subnet separation for public vs private.
• Transit Gateway inside EU only: Use an AWS Transit Gateway deployed in the sovereign region to centralize routing and VPN/Direct Connect attachments. Do not attach gateways that cross to other regions outside the EU OU.
• VPC endpoints: Use S3 Gateway endpoints and Interface endpoints for service access. Lock S3 access to the VPC endpoint in bucket policies.
• Direct Connect / DX: If you need private connectivity from on‑prem, terminate Direct Connect at EU PoPs and attach to the sovereign Transit Gateway. Record the ASNs and ensure DX locations are EU-located.
• No automatic internet egress: Avoid default internet access for workloads that handle regulated data. Route egress through controlled NATs or egress appliances in the sovereign region and record flows with VPC Flow Logs.

Sample bucket policy: restrict S3 to VPC endpoint and region

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "DenyNonVpcAndNonRegion",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:*",
      "Resource": ["arn:aws:s3:::my-sensitive-bucket","arn:aws:s3:::my-sensitive-bucket/*"],
      "Condition": {
        "StringNotEquals": {"aws:RequestedRegion": "eu-sovereign-1"},
        "Null": {"aws:SourceVpc": "true"}
      }
    }
  ]
}

3) Storage patterns — enforce in-region residency and encryption

Each storage class has its quirks. The goal: make it impossible to accidentally replicate or snapshot data outside the sovereign boundary.

S3 (object storage)

• Always enable Block Public Access and apply bucket policies that deny requests that don't originate from approved VPC endpoints or IP ranges.
• Use SSE-KMS with a CMK whose key policy and key material are constrained to the sovereign region; consider CloudHSM / BYOK for extra assurance.
• Disable or tightly control cross-region replication. If replication is necessary, replicate only to other EU sovereign region endpoints.
• Use S3 Object Lock and retention modes for WORM requirements; store the lock governance metadata in-region.

Block and file storage (EBS, EFS, FSx)

• Enable default encryption with KMS CMKs from the sovereign region.
• Restrict snapshot copy operations with IAM and SCPs so snapshots cannot be copied to other regions.
• Use lifecycle policies that write backups to an in-region backup vault (see AWS Backup) with immutability options.

Archival

Ensure tape/archival classes (Glacier / Archive tiers) are located in-region. Verify the archival provider’s physical locations are EU‑based.

4) IAM and key management — the cryptographic boundary

IAM and KMS are your proof points. Treat them as compliance artifacts and design policies accordingly.

IAM

• Use AWS IAM Identity Center or an EU-hosted IdP for SSO. Prefer identity providers that store identity metadata in the EU.
• Enforce Permission Boundaries and role session duration limits. Require MFA for interactive roles and use short-lived credentials for programmatic access.
• Use resource-based policies and explicit deny statements for actions that could move data out of the sovereign region (e.g., ec2:CopySnapshot to non-EU regions, s3:ReplicateObject to non-EU).

KMS & CloudHSM

• Create CMKs in the sovereign region and put strict key policies that only allow principals from the sovereign OU to use them.
• For the highest assurance, use AWS CloudHSM in the sovereign region with BYOK to control key material. Maintain audit logs for HSM operations.
• Use KMS grants and never store unencrypted key material outside the region.

Example KMS key policy snippet

{
  "Version": "2012-10-17",
  "Statement": [{
    "Sid": "AllowOrgUse",
    "Effect": "Allow",
    "Principal": {"AWS": "arn:aws:iam::111122223333:root"},
    "Action": ["kms:Encrypt","kms:Decrypt","kms:GenerateDataKey*"],
    "Resource": "*",
    "Condition": {"StringEquals": {"aws:PrincipalOrgID": "o-abc123"}}
  }]
}

5) Logging, monitoring and immutable evidence

Regulators will want logs. Make them reliable, immutable and in-region.

• Enable CloudTrail across all accounts and aggregate logs into a central, write-once S3 bucket inside the sovereign OU. Protect with S3 Object Lock and versioning.
• Deploy AWS Config Recorder and aggregate configuration snapshots into-region. Use aggregated Config rules to detect non-compliant resources.
• Run GuardDuty, Security Hub and Detective in the sovereign region and forward findings to a SIEM hosted in the EU.
• Capture VPC Flow Logs and DNS logs and ensure retention policies meet audit requirements.

6) Data flows and cross-border controls

Document and enforce every allowed cross-border flow. Anything else = denied by default.

• Classify data by sensitivity and legal constraints. Use this to decide which datasets are EU-only.
• For permitted exports, apply application-level encryption where only the recipient holds the key (end-to-end encryption).
• Use explicit allowlists for external integrations and require legal sign-off before enabling any non-EU endpoint.

Practical rule: if you can’t produce a signed, auditable business case for a cross-border flow, block it.

7) Migration checklist — move with confidence

1. Inventory: discover all data stores, metadata flows and backups (use tools like AWS Application Discovery Service or open-source scanners).
2. Classify: tag datasets by residency requirement and retention policy.
3. Design landing zones and SCPs in a test OU. Validate with policy-as-code tools (e.g., Terraform + Sentinel or OPA).
4. Move compute and data using in-region services — for DBs use AWS DMS inside the sovereign region and test replication endpoints carefully.
5. Cutover: freeze writes, replicate final deltas, validate consistency, then retire previous foreign-region copies (document destruction).
6. Evidence: generate an access and transfer log package for the change control board and auditors.

8) Performance, cost and operational trade-offs

Choosing EU-only residency can cost more (less global edge caching, potentially higher compute costs). Manage it with:

• Edge strategy: use EU CDN PoPs; if CloudFront edge nodes run globally, consider regional caching appliances or configure geo-restrictions and origin shields inside EU.
• Latency: place data and compute together — co-locate latency-sensitive services in the same AZs in the sovereign region.
• Cost: use lifecycle policies to tier cold data and enable intelligent-tiering for S3 with in-region archival.

9) Advanced strategies and automation

• Automate compliance validation using AWS Config Rules, Terraform and CI pipelines that run policy-as-code checks on PRs.
• Use HSM-backed signing for attestation reports that can be presented to auditors.
• Adopt split-key or escrow models with escrow agents inside the EU for recovery — maintain tamper evidence and clear SLAs.
• Build reusable IaC modules (Terraform modules / AWS CDK) to provision “sovereign-ready” stacks to reduce human error.

10) Example — a bank’s migration pattern (concise case study)

Situation: a European bank with customer PII currently split across EU and non-EU AWS regions. Goal: move PII into AWS European Sovereign Cloud and prove residency.

Approach summary:

1. Created a sovereign OU; implemented SCP to block non-EU region creation.
2. Provisioned Transit Gateway in the sovereign region; established DX to EU on-prem locations.
3. Exported PII data using DMS to RDS instances in the sovereign region; snapshots were encrypted with a CloudHSM-backed CMK.
4. Retained immutable logs in a central S3 bucket with Object Lock and provided auditors with signed attestations.
5. Result: auditors validated that backups, logs and keys never left the EU boundary.

Actionable takeaways — quick checklist

• Deploy a sovereign OU and attach an SCP that denies non-EU regions.
• Create CMKs in-region and consider CloudHSM for BYOK.
• Lock S3 access to VPC endpoints and enable Object Lock for evidence retention.
• Aggregate CloudTrail, Config and Flow Logs to an in-region, immutable S3 bucket.
• Use Control Tower / Landing Zone templates to standardize deployments.
• Document and approve any permitted cross-border flows; everything else remains blocked.

Common pitfalls to avoid

• Assuming CDN/edge nodes don’t cache sensitive payloads — verify geolocation of caches and use tokenized responses.
• Relying solely on contractual assurances without technical enforcement (SCPs, KMS boundaries, endpoint policies).
• Not protecting backups and snapshots — these are common leak vectors.
• Neglecting identity provider location — SSO metadata and logs can leak outside the EU.

Final checklist for first 30 days

1. Set up the EU sovereign OU and test SCPs in staging.
2. Provision central logging and enforce S3 Object Lock on logs.
3. Configure per-workload VPCs with endpoints and restrict S3 access to endpoints.
4. Create CMKs in-region and evaluate CloudHSM if required.
5. Run automated compliance checks (Config rules, policy-as-code) in CI/CD.

Closing notes — legal & operational caveats

Technical controls are necessary but not sufficient. Always pair the blueprint with:

• Legal review of contracts and DPA amendments reflecting the sovereign environment.
• Operational runbooks for audits and incident response that reference region-bound delegation and escrow procedures.
• Regular third-party attestation (pen tests, compliance audits) whose reports are stored in-region.

Call to action

If you’re planning or executing an EU sovereignty migration, don’t improvise. Download our ready-to-run Terraform modules and a pre-built Control Tower landing zone for the AWS European Sovereign Cloud, or schedule a design session with storages.cloud’s architects to convert this blueprint into a validated production rollout tailored to your compliance needs.

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