🎨 Exercise 04: Add Parameters & Decorators in Bicep – Your Templates Just Got Smarter

If writing Bicep templates feels like setting up IKEA furniture — decorators are the little labels and warnings on the box that help you avoid a build gone wrong 😅

💭 The Scenario

You’re helping the HR department move their app to Azure. To do this the right way, you’re setting up a Bicep template that deploys:

• An App Service Plan (like the server where the app will live)
• An App Service App (the actual HR app that runs on it)

But instead of just typing values willy-nilly, you’re adding rules and helpful hints to guide whoever deploys this in the future.

That’s where decorators come in. Let’s go!

🛠️ Step 1: Build the Template Skeleton

In VS Code:

1. Create a file named main.bicep
2. Add this starter code:

param environmentName string = 'dev'
param solutionName string = 'toyhr${uniqueString(resourceGroup().id)}'
param appServicePlanInstanceCount int = 1
param appServicePlanSku object = {
  name: 'F1'
  tier: 'Free'
}
param location string = 'westus'

var appServicePlanName = '${environmentName}-${solutionName}-plan'
var appServiceAppName = '${environmentName}-${solutionName}-app'

💡 What’s Happening Here?

• You're creating parameters that allow flexibility when deploying.
• uniqueString() is like giving your template a fingerprint — it ensures you get a unique name without manually editing anything.
• You’re also setting up variables to combine parameters into valid resource names.

🧱 Step 2: Add the Resources

Now let’s tell Azure what to build:

resource appServicePlan 'Microsoft.Web/serverfarms@2024-04-01' = {
  name: appServicePlanName
  location: location
  sku: {
    name: appServicePlanSku.name
    tier: appServicePlanSku.tier
    capacity: appServicePlanInstanceCount
  }
}

resource appServiceApp 'Microsoft.Web/sites@2024-04-01' = {
  name: appServiceAppName
  location: location
  properties: {
    serverFarmId: appServicePlan.id
    httpsOnly: true
  }
}

So far, so good!

🪄 Step 3: Add Descriptions & Guardrails

Imagine you’re writing this template for your future self (or a teammate). You want to:

• Show a description for each parameter
• Prevent invalid inputs (like someone typing “banana” for an environment name 🍌)

Let’s clean up those parameters:

@description('The name of the environment. This must be dev, test, or prod.')
@allowed([
  'dev'
  'test'
  'prod'
])
param environmentName string = 'dev'

@description('The unique name of the solution. Used to ensure resource names are globally unique.')
@minLength(5)
@maxLength(30)
param solutionName string = 'toyhr${uniqueString(resourceGroup().id)}'

@description('The number of App Service plan instances.')
@minValue(1)
@maxValue(10)
param appServicePlanInstanceCount int = 1

@description('The name and tier of the App Service plan SKU.')
param appServicePlanSku object = {
  name: 'F1'
  tier: 'Free'
}

@description('The Azure region for deployment.')
param location string = 'westus'

✨ Why Decorators Rock

Think of decorators as:

• Tooltips for anyone using your template
• Seatbelts that stop people from entering bad values
• Training wheels for safe, repeatable deployments

🚀 Step 4: Deploy It to Azure

1. Install & Upgrade Bicep (if needed)

az bicep install && az bicep upgrade

2. Log in

az login

✅ I just hit Enter because my default subscription was already selected.

3. Create a Resource Group

az group create --name BicepRG --location westus

4. Deploy!

az deployment group create \
  --resource-group BicepRG \
  --name main \
  --template-file main.bicep

Boom. Now you’re deploying a safe, validated, and well-documented infrastructure setup 💪

🧠 In Short: What You Learned

✅ Pro Tip: Fixing Common Errors

I got a few errors at first because I accidentally used environment instead of environmentName.

If that happens, VS Code will guide you with squiggly lines — and the terminal will be very vocal 😅

Make sure your variable names match exactly, especially if you're doing interpolation like this:

var appServicePlanName = '${environmentName}-${solutionName}-plan'

🏁 Done & Deployed

Head to the Azure Portal, find your BicepRG resource group, and check:

• ✅ Two resources deployed
• ✅ Your parameters and values under “Inputs”
• ✅ A successful deployment log

You can even click on your App Service App, and if it’s running — open it in the browser to see the welcome page! 🎉

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Would love to hear what you're working on or learning!