tools-only ADR-0001: Cost-Optimized N-Tier Azure Architecture for Dev Environment
Generated by design agent | 2026-02-26
- 🔍 Context
- ✅ Decision
- 🔄 Alternatives Considered
- ⚖️ Consequences
- 🏛️ WAF Pillar Analysis
- 🔒 Compliance Considerations
- 📝 Implementation Notes
Status: Accepted Date: 2026-02-26 Deciders: Project Owner, Architect Agent
🔍 Context
The project requires a very small ecommerce storefront on Azure with Terraform IaC, low initial traffic (<100 users), and strong cost discipline. The target monthly envelope is well below the soft budget ceiling while preserving baseline security and operability.
✅ Decision
Adopt a cost-optimized n-tier architecture:
- Frontend: Azure Static Web App (Free) in
westeurope - API: Azure App Service Plan B1 (Linux) in
swedencentral - Data: Azure SQL Database Basic (5 DTU) in
swedencentral - Security/Ops: Key Vault, Application Insights, Log Analytics
- Identity: Microsoft Entra External ID
- IaC: Terraform (
azurerm ~> 4.0) with remote state in Azure Blob Storage
🔄 Alternatives Considered
| Option | Pros | Cons | WAF Impact |
|---|---|---|---|
| Higher baseline SKUs (S1/S0) from day one | Better headroom, autoscale readiness | Higher recurring cost at low traffic | Reliability +, Cost - |
| Container Apps + SQL serverless | Flexible scaling | More complexity for initial MVP | Performance +, Ops - |
| VM-based 3-tier stack | Full control | High ops overhead, overkill for MVP | Ops -, Cost - |
⚖️ Consequences
Positive
- Keeps expected spend low while supporting core storefront capabilities
- Uses managed PaaS services to reduce platform maintenance burden
- Preserves a clear upgrade path for reliability/security hardening
Negative
- Single-region and non-AZ posture in dev introduces higher outage risk
- Basic tiers limit burst capacity and advanced enterprise controls
- Some GDPR controls remain application-layer responsibilities
Neutral
- Architecture is intentionally biased for MVP economics over resiliency
- Governance-policy validation is deferred to implementation planning phase
🏛️ WAF Pillar Analysis
| Pillar | Impact | Notes |
|---|---|---|
| Security | Mixed | Baseline controls in place; advanced network isolation deferred |
| Reliability | Negative | Single region and no AZ in dev |
| Performance | Positive | Suitable for low-concurrency workload |
| Cost Optimization | Strong Positive | Lowest viable SKUs selected |
| Operational Excellence | Mixed | IaC + monitoring present; CI/CD and runbooks still pending |
🔒 Compliance Considerations
- GDPR controls are mapped in architecture assessment with clear infra vs app-layer ownership.
- Data residency remains in EU regions (
swedencentral,westeurope). - Breach notification flow is supported via Azure Monitor alerting pipeline.
📝 Implementation Notes
- Keep this decision for dev and pre-production stages.
- Trigger review when concurrency exceeds thresholds or availability SLO is raised.
- Capture policy outcomes in Step 4 governance constraints artifact.