Instruction file imported from percebus/ai-tooling (.github/instructions/terraform-sap-btp.instructions.md). Copyright stays with the author.

Terraform on SAP BTP – Best Practices & Conventions

Core Principles

Keep Terraform code minimal, modular, repeatable, secure, and auditable. Always version control Terraform HCL and never version control generated state.

Security

Mandatory:

• Use the latest stable Terraform CLI and provider versions; upgrade proactively for security patches.
• Do NOT commit secrets, credentials, certificates, Terraform state, or plan output artifacts.
• Mark all secret variables and outputs as sensitive = true.
• Prefer ephemeral / write‑only provider auth (Terraform >= 1.11) so secrets never persist in state.
• Minimize sensitive outputs; emit only what downstream automation truly needs.
• Continuously scan with tfsec, trivy, checkov (pick at least one) in CI.
• Periodically review provider credentials, rotate keys, and enable MFA where supported.

Modularity

Structure for clarity and speed:

• Split by logical domain (e.g., entitlements, service instances) – NOT by environment.
• Use modules for reusable multi‑resource patterns only; avoid single‑resource wrapper modules.
• Keep module hierarchy shallow; avoid deep nesting and circular dependencies.
• Expose only essential cross‑module data via outputs (mark sensitive when required).

Maintainability

Aim for explicit > implicit.

• Comment WHY, not WHAT; avoid restating obvious resource attributes.
• Parameterize (variables) instead of hard‑coding; provide defaults only when sensible.
• Prefer data sources for external existing infra; never for resources just created in same root – use outputs.
• Avoid data sources in generic reusable modules; require inputs instead.
• Remove unused / slow data sources; they degrade plan time.
• Use locals for derived or repeated expressions to centralize logic.

Style & Formatting

General

• Descriptive, consistent names for resources, variables, outputs.
• snake_case for variables & locals.
• 2 spaces indentation; run terraform fmt -recursive.

Layout & Files

Recommended structure:

my-sap-btp-app/
├── infra/                      # Root module
│   ├── main.tf                 # Core resources (split by domain when large)
│   ├── variables.tf            # Inputs
│   ├── outputs.tf              # Outputs
│   ├── provider.tf             # Provider config(s)
│   ├── locals.tf               # Local/derived values
│   └── environments/           # Environment var files only
│       ├── dev.tfvars
│       ├── test.tfvars
│       └── prod.tfvars
├── .github/workflows/          # CI/CD (if GitHub)
└── README.md                   # Documentation

Rules:

• Do NOT create separate branches/repos/folders per environment (antipattern).
• Keep environment drift minimal; encode differences in *.tfvars files only.
• Split oversized main.tf / variables.tf into logically named fragments (e.g., main_services.tf, variables_services.tf). Keep naming consistent.

Resource Block Organization

Order (top → bottom): optional depends_on, then count/for_each, then attributes, finally lifecycle.

• Use depends_on ONLY when Terraform cannot infer dependency (e.g., data source needs entitlement).
• Use count for optional single resource; for_each for multiple instances keyed by a map for stable addresses.
• Group attributes: required first, then optional; blank lines between logical sections.
• Alphabetize within a section for faster scanning.

Variables

• Every variable: explicit type, non‑empty description.
• Prefer concrete types (object, map(string), etc.) over any.
• Avoid null defaults for collections; use empty lists/maps instead.

Locals

• Centralize computed or repeated expressions.
• Group related values into object locals for cohesion.

Outputs

• Expose only what downstream modules/automation consume.
• Mark secrets sensitive = true.
• Always give a clear description.

Formatting & Linting

• Run terraform fmt -recursive (required in CI).
• Enforce tflint (and optionally terraform validate) in pre‑commit / CI.

Documentation

Mandatory:

• description + type on all variables & outputs.
• A concise root README.md: purpose, prerequisites, auth model, usage (init/plan/apply), testing, rollback.
• Generate module docs with terraform-docs (add to CI if possible).
• Comments only where they clarify non-obvious decisions or constraints.

State Management

• Use a remote backend supporting locking (e.g., Terraform Cloud, AWS S3, GCS, Azure Storage). Avoid SAP BTP Object Store (insufficient capabilities for reliable locking & security).
• NEVER commit *.tfstate or backups.
• Encrypt state at rest & in transit; restrict access by principle of least privilege.

Validation

• Run terraform validate (syntax & internal checks) before committing.
• Confirm with user before terraform plan (requires auth & global account subdomain). Provide auth via env vars or tfvars; NEVER inline secrets in provider blocks.
• Test in non‑prod first; ensure idempotent applies.

Testing

• Use Terraform test framework (*.tftest.hcl) for module logic & invariants.
• Cover success & failure paths; keep tests stateless/idempotent.
• Prefer mocking external data sources where feasible.

SAP BTP Provider Specifics

Guidelines:

• Resolve service plan IDs using data "btp_subaccount_service_plan" and reference serviceplan_id from that data source.

Example:

data "btp_subaccount_service_plan" "example" {
  subaccount_id = var.subaccount_id
  service_name  = "your_service_name"
  plan_name     = "your_plan_name"
}

resource "btp_subaccount_service_instance" "example" {
  subaccount_id  = var.subaccount_id
  serviceplan_id = data.btp_subaccount_service_plan.example.id
  name           = "my-example-instance"
}

Explicit dependencies (provider cannot infer):

resource "btp_subaccount_entitlement" "example" {
  subaccount_id = var.subaccount_id
  service_name  = "your_service_name"
  plan_name     = "your_plan_name"
}

data "btp_subaccount_service_plan" "example" {
  subaccount_id = var.subaccount_id
  service_name  = "your_service_name"
  plan_name     = "your_plan_name"
  depends_on    = [btp_subaccount_entitlement.example]
}

Subscriptions also depend on entitlements; add depends_on when the provider cannot infer linkage via attributes (match service_name/plan_name ↔ app_name).

Tool Integration

HashiCorp Terraform MCP Server

Use the Terraform MCP Server for interactive schema lookup, resource block drafting, and validation.

1. Install & run server (see https://github.com/mcp/hashicorp/terraform-mcp-server).
2. Add it as a tool in your Copilot / MCP client configuration.
3. Query provider schema (e.g., list resources, data sources) before authoring.
4. Generate draft resource blocks, then refine manually for naming & tagging standards.
5. Validate plan summaries (never include secrets); confirm diff with reviewer before apply.

Terraform Registry

Reference the SAP BTP provider docs: https://registry.terraform.io/providers/SAP/btp/latest/docs for authoritative resource & data source fields. Cross‑check MCP responses with registry docs if uncertain.

Anti‑Patterns (Avoid)

Configuration:

• Hard‑coded environment‑specific values (use variables & tfvars).
• Routine use of terraform import (migration only).
• Deep / opaque conditional logic and dynamic blocks that reduce clarity.
• local-exec provisioners except for unavoidable integration gaps.
• Mixing SAP BTP provider with Cloud Foundry provider in the same root unless explicitly justified (split modules).

Security:

• Storing secrets in HCL, state, or VCS.
• Disabling encryption, validation, or scanning for speed.
• Using default passwords/keys or reusing credentials across environments.

Operational:

• Direct production applies without prior non‑prod validation.
• Manual drift changes outside Terraform.
• Ignoring state inconsistencies / corruption symptoms.
• Running production applies from uncontrolled local laptops (use CI/CD or approved runners).
• Reading business data from raw *.tfstate instead of outputs / data sources.

All changes must flow through Terraform CLI + HCL – never mutate state manually.