Describe how you would architect a secure, multi‑tenant SaaS platform that ensures strict data isolation, compliance with GDPR and PCI DSS, and high availability, using microservices and container orchestration.

Use STRIDE, NIST CSF, and TOGAF ADM. 1) Define security domains and data classification. 2) Implement IAM with role‑based access control and identity federation. 3) Deploy microservices in Kubernetes with namespaces, network policies, and pod security contexts. 4) Enforce encryption at rest (KMS) and in transit (TLS). 5) Build multi‑region HA with load balancers, automated failover, and continuous monitoring via Prometheus and SIEM. 6) Integrate automated compliance checks and audit logging.

I would start by applying the STRIDE threat model to identify spoofing, tampering, repudiation, information disclosure, denial of service, and elevation of privilege risks across the SaaS stack. Using NIST CSF, I map these risks to protective controls and align them with TOGAF ADM phases to ensure architectural coherence. Data classification drives isolation: each tenant’s data resides in a dedicated Kubernetes namespace with strict network policies and pod security contexts. IAM is handled via an identity federation layer (e.g., SAML/OIDC) feeding into role‑based access control, ensuring least privilege. Encryption is enforced at rest using a cloud KMS and in transit with TLS 1.3. High availability is achieved through multi‑region deployments, automated health checks, and load balancers that route traffic based on latency and health. Continuous monitoring with Prometheus, Grafana, and a SIEM feeds into automated remediation pipelines, while audit logs are immutable and stored in a tamper‑evident repository. Compliance with GDPR and PCI DSS is maintained through automated policy enforcement, data residency controls, and regular penetration testing.