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Function App deploy fails: service_plan_id is required

One-sentence summary: saif-event-subscriber-service needs your team's opt-in Elastic Premium -functions App Service plan, and until the platform team enables it the plan ID is null, so Terraform rejects the Function App with a missing-required-argument error.

🚨 Symptom

Deploying saif-event-subscriber-service fails during terraform plan (or terraform apply) with:

Error: Missing required argument

  with module.function_app.azurerm_linux_function_app.this,
  on .terraform/modules/function_app/modules/functionapp_linux/main.tf line 5, in resource "azurerm_linux_function_app" "this":
   5:   service_plan_id               = var.service_plan_id

The argument "service_plan_id" is required, but no definition was found.

The error points at the third-party functionapp_linux module rather than at your service, so it reads like a module bug. It isn't — the plan ID your service passed in was null. Line numbers shift between functionapp_linux versions; the resource address and the service_plan_id wording stay the same.

This appears in the event subscriber's Deploy pipeline Terraform step, and locally when running Terraform against the service.

📌 Applies to

Aspect Value
Component Terraform — saif-event-subscriber-service
Module versions functionapp_linux ~> 5.1.1; saif-resources //modules/environment
Related versions Check the version compatibility matrix

🧠 Cause

The Elastic Premium (EP) plan that Function Apps run on is opt-in per team, because EP plans bill even when idle. Teams that have never deployed a Function App don't have one.

saif-event-subscriber-service reads the plan from module.environment.context.team_services.function_app_service_plan_id, which the environment module resolves as null when the team hasn't enabled it. That null flows into functionapp_linux's service_plan_id, which is a plain string variable with no null check, so it reaches azurerm_linux_function_app — where the azurerm provider requires it. Terraform blocks the plan there.

Nothing is misconfigured in your service. The prerequisite just isn't provisioned yet.

✅ Fix

The plan lives in the platform-owned cloud-foundations repo, so request it rather than changing your service:

  1. Ask the platform team to enable your team's Function App service plan, through either channel:

  2. Include in the request:

    • Your team name
    • The environments you need it in (test, qa, uat, prod)
    • That this is the opt-in Elastic Premium -functions plan, needed for saif-event-subscriber-service
    • Why the workload needs it, since EP plans carry a standing cost

  3. Wait for confirmation that the team stack has been applied, then re-run the deploy.

On the platform side this enables the -functions plan for your team and creates a Linux Elastic Premium plan named <team-service-plan>-functions with elastic scaling. You don't make this change yourself, and you don't need to modify your service's Terraform.

🔬 Verify

After the team stack is applied, re-run terraform plan for the service. The Missing required argument error is gone and the plan shows the Function App to add:

# module.function_app.azurerm_linux_function_app.this will be created
+ resource "azurerm_linux_function_app" "this" {
    + service_plan_id = "/subscriptions/.../providers/Microsoft.Web/serverfarms/<team-service-plan>-functions"

You can also confirm the plan exists in your team's resource group in the Azure portal: an App Service plan whose name ends in -functions with an EP SKU.