Bring together repo structure, state strategy, module strategy, workflow, security, and guardrails into a coherent platform foundation.

Foundations

# Accounts: separate AWS accounts per env (and per business unit) — hard isolation

# State: per (account x layer x service); S3+KMS+DynamoDB (or TF Cloud); versioned+locked

# Layers: network → data → platform → apps, connected via remote-state/data sources

# Modules: versioned 'golden' modules in a registry (the paved road)

Workflow & guardrails

# CI: plan-on-PR (diff comment), gated apply-on-merge with saved plan, CODEOWNERS

# Auth: OIDC federation, per-env scoped roles, permission boundaries (no static keys)

# Policy-as-code: Sentinel/OPA org-wide (no public exposure, required tags, encryption)

# Visibility: Infracost (cost on PRs), scheduled drift detection, audit via Git + state

Start with account-level isolation (separate accounts per environment) for the strongest blast-radius boundary, then partition state per account × layer × service with an encrypted, versioned, locked backend. Provide golden modules in a registry so teams compose a paved road rather than reinventing. Standardize the workflow (plan-on-PR, gated apply of saved plans, CODEOWNERS) and auth (OIDC, scoped per-env roles, permission boundaries). Enforce guardrails with org-wide policy-as-code, and add visibility with cost estimation, drift detection, and Git+state audit trails. The objective: self-service infrastructure where the secure, compliant, cost-aware path is the easy default.

Interview tip: structure the answer as isolation (accounts) → state strategy → module/paved-road → workflow → security/auth → policy guardrails → cost/drift visibility. Emphasizing "the safe path is the easy path" and managing the platform itself as code is exactly the staff/principal-level framing for a Platform Engineering interview.