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OSDU SPI Infrastructure

ADR-0001: Three-Layer Deployment Model

Status: Accepted
Date: 2026-03-15
Deciders: danielscholl

Context and Problem Statement

Section titled “Context and Problem Statement”

Deploying OSDU on AKS requires provisioning Azure PaaS resources, installing cluster operators (cert-manager, ECK, CNPG), and deploying application workloads. A single Terraform state creates fragile coupling — a chart upgrade can trigger unnecessary re-evaluation of Azure infrastructure, and foundation operators must exist before application Helm releases can reference their CRDs.

Decision Drivers

Section titled “Decision Drivers”
  • CRD ordering: Helm releases for Elasticsearch, PostgreSQL, etc. require CRDs from ECK/CNPG to exist at plan time
  • Blast radius: infrastructure changes should not re-evaluate application releases
  • Iteration speed: developers need to redeploy the stack layer without re-running a 15-minute infra provision
  • azd orchestration must drive all layers through lifecycle hooks

Considered Options

Section titled “Considered Options”
  1. Single Terraform root module
  2. Three-layer model with independent state (infra → foundation → stack)
  3. GitOps with Flux/ArgoCD

Decision Outcome

Section titled “Decision Outcome”

Chosen option: Three-layer model with independent state, because it isolates blast radius per layer, respects CRD ordering, and enables fast stack-only iteration via azd deploy while azd provision handles infrastructure.

Layer 3 supports two independent stack variants — spi-stack (Azure SPI with PaaS backends) and cimpl-stack (fully in-cluster CIMPL) — that can be deployed individually or side-by-side on the same cluster. Both share the same Layer 1 infrastructure and Layer 2 foundation.

Consequences

Section titled “Consequences”
  • Good: Stack redeployment takes ~5 minutes instead of re-evaluating all 3 layers
  • Good: Foundation CRDs are guaranteed to exist before stack Helm releases reference them
  • Good: infra-access layer enables privileged RBAC bootstrap with minimal scope
  • Good: Multiple stack variants share foundation without duplication
  • Bad: Cross-layer data passing requires Terraform outputs → azd env → Terraform variables plumbing
  • Bad: azd down must tear down in reverse order via lifecycle hooks