AWS European Sovereign Cloud: A Technical Checklist for Secure Migration

Hook — Why this checklist matters now

If you're an architect responsible for migrating regulated EU workloads to cloud, you face a narrow margin for error: misconfigured keys, an overlooked replication rule, or a missing contractual clause can convert a compliance project into a major breach and regulatory headache. In 2026 the stakes for AWS Sovereign Cloud migrations are higher — regulators and customers expect demonstrable, technical isolation plus ironclad contractual assurances. This checklist is a practical, prioritized playbook for migration teams to deliver a secure, auditable move into the AWS European Sovereign Cloud.

Executive summary (most important first)

Start here if you have 30 seconds. The migration must prove four things to technical and legal stakeholders:

• Cryptographic sovereignty: KMS separation and key custody reside in the EU, with strict access controls and auditable key events.
• Network and region isolation: No accidental egress to non-EU regions or public internet paths; all interconnects terminate in EU-only infrastructure.
• Legal and contractual assurances: DPA, demonstrable personnel restrictions, subcontractor visibility, audit rights and breach notification commitments locked into contract.
• Complete, tamper-evident logging: Audit trails for config changes, KMS usage, and network flows that are retained and stored inside the sovereign cloud region.

Below you’ll find a detailed, actionable checklist for architects covering design decisions, configuration controls, migration steps and validation tests tailored to the AWS European Sovereign Cloud launched in early 2026 and evolving regulatory guidance through late 2025.

Context: 2025–2026 trends shaping sovereign cloud migrations

Late 2025 and early 2026 saw EU governments and large enterprises accelerate sovereign cloud pilots and demand stronger controls over data location, personnel access, and cryptographic keys. AWS’s January 2026 launch of the AWS European Sovereign Cloud emphasized physical and logical separation and new contractual protections designed to meet these expectations.

"Designed to help customers meet the EU’s sovereignty requirements, the AWS European Sovereign Cloud is physically and logically separate from other AWS regions."

At the same time, regulators (including national supervisory authorities and the EDPB) increased scrutiny of cross-border transfer risk assessments and technical controls for preventing unauthorized access. That means technical architecture must be paired with contractual and operational commitments — your migration plan needs both.

Migration checklist overview (high level)

1. Pre-migration: legal & technical readiness assessment
2. Design: KMS and key custody model
3. Design: network topology and interconnects
4. Design: logging, monitoring, export controls
5. Data flows: replication, backups, and cross-region restrictions
6. Contractual: DPAs, audit rights, personnel & subcontractor clauses
7. Migration: tools, incremental migration, validations
8. Post-migration: audits, red-team, compliance attestations

KMS separation: architecture options and checklist

Cryptographic control is the single most visible indicator of sovereignty. Architects must choose how keys are generated, stored, and controlled.

Recommended key custody models

• Cloud-native KMS (region-bound): Use AWS KMS keys created and stored in the Sovereign Cloud region, with key policies that deny use outside the region and strict IAM controls.
• Dedicated HSM (CloudHSM) in-EU: For higher assurance, provision CloudHSM clusters physically located in the sovereign region; use KMS custom key store backed by CloudHSM.
• External Key Manager (XKS) / Bring-Your-Own-Key (BYOK): If you require external key material or full customer custody, integrate an EKM inside EU boundaries or a network-local HSM appliance that keeps key generation and export in-scope.

Practical KMS checklist for architects

• Generate and store all root/master keys in EU-only KMS/CloudHSM instances.
• Implement KMS key policies with explicit Deny statements that block decrypt/encrypt operations if the request principal or request region is outside the sovereign region.
• Enable CloudTrail for all KMS API calls and route logs to an immutable S3 bucket in the sovereign region with object lock enabled (WORM) where requirements apply.
• Enforce multi-person approval (split custody) for key import, rotation and deletion using AWS Lambda workflow or KMS multi-account MFA controls for highly sensitive keys.
• Use CMKs for data encryption and never store plaintext keys outside the EU region; validate that third-party connectors don’t cache key material locally.
• Document access processes and retain key lifecycle logs for regulatory audit windows (e.g., 5–7 years depending on sector).
• Run regular key policy & IAM permission reviews and automated compliance checks (IAM Access Analyzer, automated guardrails).

Network isolation: design patterns and controls

Network misconfiguration is one of the top causes of accidental data exposure during and after migration. For sovereign cloud, block all unintended egress paths by design.

Core network controls to implement

• VPC-per-environment: Separate VPCs for prod, pre-prod, and non-sensitive workloads with transit architectures that enforce central inspection.
• Private connectivity: Use Direct Connect (private VIF) or AWS Partner interconnects terminating in EU-only PoPs; avoid Internet-based tunnels for primary data channels.
• VPC Endpoints and PrivateLink: Disable public S3/Gateway endpoints; use interface or gateway endpoints restricted to the region to access AWS services privately.
• Egress controls: Centralized egress via NATs with strict egress allowlists; implement proxy with TLS inspection if policy requires.
• DNS controls: Use Route 53 Resolver inbound/outbound endpoints restricted to EU IP ranges; block non-EU DNS resolvers.
• Network firewalling: AWS Network Firewall or third-party NGFW with rules that deny traffic to non-EU IP prefixes and non-authorized regions.

Network checklist for architects

• Design the transit architecture so all lateral and north-south traffic passes through EU-bound inspection and logging points.
• Lockdown security groups and NACLs with deny-by-default posture; enforce least-privilege ports and protocols.
• Implement flow logs (VPC Flow Logs) centralized to the sovereign-region logging bucket/collector with retention and integrity controls.
• Use resource policies on endpoints to prevent cross-region access (e.g., S3 bucket policies deny if aws:SourceRegion != sovereign-region).
• Include network-level tests in migration cutover (connectivity to EU endpoints only, no leakage detected by public scanners).

Logging, export controls and immutable audit trails

Regulators expect auditable trails showing who accessed what, when, and from where. In 2026, the expectation is immutable, region-bound logs with tamper detection.

Logging architecture

• Centralize CloudTrail, Config, CloudWatch Logs, VPC Flow Logs and KMS logs into an encrypted, access-restricted S3 bucket in the sovereign region.
• Enable multi-account aggregation (AWS Organizations) with cross-account roles that keep log storage in the EU region only.
• Enable S3 Object Lock with governance or compliance mode for tamper-evident retention; consider backups to an isolated log vault.
• Feed logs into an EU-hosted SIEM / XDR for real-time detection; ensure SIEM processing occurs inside the sovereign boundary.
• Implement alerting for key events: KMS key usage outside expected principals, config change to security groups, creation of cross-region replication rules, IAM policy escalations.

Export controls and legal considerations

• Identify whether any data subject to export control or restrictions (dual-use, defense) will be migrated and work with legal teams to ensure licensing and controls — consider hybrid legal/technical playbooks for regulated datasets (hybrid oracle strategies).
• Ensure data classification maps to allowed storage/processing locations and that automated policies block export of restricted classes.
• Contractually require the provider to notify you of any law enforcement or governmental access requests, with EU-specific escalation and challenge mechanisms in place if available.

Cross-region data flows and region isolation

Architects must prevent unintentional replication or failover to non-EU regions. This requires both configuration and guardrails.

Design controls

• Disable automatic cross-region replication or enable only to explicitly approved EU sibling regions (if multi-EU-region HA is required).
• Use S3 bucket policies and replication configuration that explicitly set destination regions and deny replication to non-EU destinations.
• Configure RDS, DynamoDB, and managed services to prohibit read replicas in non-EU regions; enforce via service control policies (SCPs) in AWS Organizations.
• Use IAM condition keys (aws:RequestedRegion or aws:SourceVpc, where available) to deny operations originating outside the sovereign region.

Cross-region checklist

• Inventory all services that perform automated backups or replication; verify destination region is within EU-only allowlist.
• Deploy guardrails as SCPs and Service Control Rules that prevent resource creation in non-authorized regions for accounts subject to sovereignty.
• Test failover/cutover plans that use only EU endpoints — simulate disaster scenarios and validate no telemetry leaves the EU.
• For DR, prefer EU-to-EU replication or cold DR with encrypted, offline transfer mechanisms under documented legal process.

Contractual assurances & auditability

Technical controls must be backed by contractual commitments. For sovereign migration, architects should collaborate with legal and procurement to negotiate specific clauses.

Key contractual items to include

• Data Processing Addendum (DPA): Clear location commitment for storage and processing within EU sovereign cloud regions.
• Personnel restrictions: Commitments that only personnel authorized and resident in the EU (or subject to EU employment law) can access customer data, if required.
• Subprocessor transparency: A list and notification process for any subcontractors and their physical locations.
• Audit rights: Right to independent audits and supply of audit reports (SOC2, ISO certification + tailored attestation for sovereign controls).
• Law enforcement handling: Notification and challenge process for governmental requests; contractual remedies for unlawful disclosure where available.
• SLAs and breach notification: Time-bound, EU-acceptable notifications for breaches and availability commitments for critical services.

Architects should map contractual clauses to measurable controls and produce an evidence matrix — this is what auditors will ask for.

Migration process: technical steps and validation

Follow an iterative, test-first approach: build a hardened landing zone, run a pilot, validate controls, then migrate production.

Step-by-step migration checklist

1. Pre-migration discovery: inventory data, classify by sensitivity and export control risk.
2. Build the landing zone: implement EU-located KMS/CloudHSM, VPC designs, endpoints, SCPs and central logging.
3. Pilot migration: move a non-critical workload; validate KMS policies, VPC isolation, endpoint usage and log retention.
4. Security validation: run automated compliance scans, config drift detection, and a focused red-team targeting egress and key access.
5. Cutover plan: incremental migration windows, traffic-swaps, DNS TTL reductions, and rollback strategies with pre-authorized steps.
6. Post-migration audit: produce an evidence pack mapping controls to contractual commitments; run a third-party attestation if required.

Validation & testing — what to prove to auditors

Be ready to demonstrate:

• KMS key origin and key usage logs showing EU-based operations only.
• Network flow records proving no egress to non-EU IP ranges during a defined observation period.
• Object-lock-backed log retention demonstrating tamper-evidence.
• Signed contractual commitments and evidence of their enforcement via technical guardrails.
• Pen test and red-team reports focused on cross-region exfiltration and key compromise scenarios.

Case study (practical example)

In late 2025 a European financial group piloted its migration of payments data to a sovereign cloud environment. Key lessons applied to the production rollout:

• They used a CloudHSM-backed KMS custom key store with HSM clusters physically provisioned in the EU region to satisfy regulator demands for customer-controlled keys.
• Transit architecture forced all outbound traffic through an EU-only inspection and egress firewall; any attempt to create replication to non-EU regions was automatically blocked by SCPs.
• Logging was centralized to an S3 bucket with object lock and access logs fed into an EU-based SIEM. The bank retained 7 years of logs in compliance with financial rules.
• Negotiated contract clauses included explicit personnel access restrictions and quarterly independent audits; technical evidence was mapped to each contractual clause to speed auditor validation.

That pilot reduced audit friction and shortened go-live time by avoiding ad-hoc contractual amendments during migration.

Common pitfalls and how to avoid them

• Assuming 'region-only' is enough: If you rely solely on region selection without KMS and guardrails, replication or backups may still cross borders. Use SCPs and resource policies.
• Overlooking third-party integrations: SaaS connectors or backup tools can pull data outside the EU. Vet every integration and enforce EU-only endpoints.
• Missing personnel clauses: Technical controls can be bypassed by privileged support access if contractual and personnel restrictions are not agreed and enforced.
• Insufficient log immutability: Storing logs in non-WORM buckets risks regulator pushback. Use object lock and retention policies.

Actionable takeaways — prioritize these first

1. Build the sovereign landing zone first: KMS/CloudHSM, VPC, endpoints, logging in EU region.
2. Apply SCPs that prevent resource creation outside approved EU regions across affected accounts.
3. Enforce KMS key policies that explicitly deny usage outside the EU and enable CloudTrail for KMS events.
4. Centralize logs to an object-lock-protected S3 bucket in the region and feed to an EU SIEM.
5. Negotiate contractual clauses — DPA, personnel controls, audit rights — before production cutover and map them to technical controls for evidence.

Looking ahead — future-proofing for 2026 and beyond

Expect regulators to demand more granular evidence of control and to standardize technical attestation requirements for sovereignty claims. Invest in automated evidence collection, continuous compliance, and immutable telemetry. Consider adopting policy-as-code and continuous validation so your architecture produces the proofs auditors will require with minimal manual effort.

Final checklist — quick reference (printable)

• KMS: EU-only key stores, CloudHSM where required, CloudTrail enabled for KMS events
• Network: Private Direct Connect, VPC endpoints, firewall egress allowlist, VPC Flow Logs centralized
• Data flows: Disable cross-region replication to non-EU; SCPs deny non-authorized regions
• Logging: Central S3 bucket in EU, object lock enabled, SIEM inside EU
• Contract: DPA with data location, personnel/subprocessor clauses, audit rights
• Validation: Pen tests for exfiltration, key compromise simulations, third-party attestation

Call to action

Moving sensitive EU workloads to the AWS European Sovereign Cloud is achievable — but only with an architect-led plan that pairs technical controls with contractual assurances and audit-ready evidence. If you’re preparing a migration, download our detailed migration template and evidence matrix, or contact smartcyber.cloud for a 1-day sovereign readiness assessment tailored to your architecture and compliance requirements.

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