Cold start and premium plan in Azure - Commands & Configuration

Introduction

Cold start happens when a cloud function or app takes extra time to start because it was inactive. Premium plans help reduce this delay by keeping resources ready to respond quickly.

When your app or function is slow to respond after being idle for some time.

When you want faster response times for users even if your app is not used constantly.

When you have unpredictable traffic and want to avoid delays during sudden spikes.

When you want to pay for reserved resources to improve performance.

When you want to avoid cold start delays in serverless functions like Azure Functions.

Commands

This command creates a Premium plan named myPremiumPlan in the eastus region. The Premium plan helps reduce cold start delays by keeping resources warm.

Terminal

az functionapp plan create --name myPremiumPlan --resource-group exampleResourceGroup --location eastus --sku EP1 --is-linux false

Expected Output

{

  "id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/exampleResourceGroup/providers/Microsoft.Web/serverfarms/myPremiumPlan",

  "location": "eastus",

  "name": "myPremiumPlan",

  "sku": {

    "name": "EP1",

    "tier": "PremiumV2"

  },

  "status": "Ready",

  "type": "Microsoft.Web/serverfarms"

}

→

--sku EP1 - Selects the Premium plan SKU to reduce cold start delays.

→

--is-linux false - Specifies the plan is for Windows-based apps.

This command creates a function app named myFunctionApp using the Premium plan myPremiumPlan. This setup helps the function app avoid cold start delays.

Terminal

az functionapp create --name myFunctionApp --storage-account mystorageaccount --plan myPremiumPlan --resource-group exampleResourceGroup --runtime dotnet

Expected Output

{

  "id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/exampleResourceGroup/providers/Microsoft.Web/sites/myFunctionApp",

  "name": "myFunctionApp",

  "resourceGroup": "exampleResourceGroup",

  "state": "Running",

  "type": "Microsoft.Web/sites"

}

→

--plan myPremiumPlan - Associates the function app with the Premium plan.

→

--runtime dotnet - Sets the runtime environment for the function app.

This command shows details about the function app to confirm it is running on the Premium plan and ready to avoid cold starts.

Terminal

az functionapp show --name myFunctionApp --resource-group exampleResourceGroup

Expected Output

{

  "name": "myFunctionApp",

  "state": "Running",

  "serverFarmId": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/exampleResourceGroup/providers/Microsoft.Web/serverfarms/myPremiumPlan",

  "kind": "functionapp",

  "location": "eastus"

}

Key Concept

If you remember nothing else from this pattern, remember: Premium plans keep your app ready to respond fast by avoiding cold start delays.

Common Mistakes

Creating a function app without specifying a Premium plan.

The app will run on a consumption plan and experience cold start delays.

Always create or assign your function app to a Premium plan to reduce cold starts.

Using the wrong SKU name when creating the plan.

The plan will not be Premium and will not reduce cold start delays.

Use the correct SKU like EP1, EP2, or EP3 for Premium plans.

Summary

Create a Premium plan to keep resources warm and reduce cold start delays.

Create your function app using the Premium plan to improve response times.

Verify your function app is running on the Premium plan to ensure cold start is minimized.

Practice

1. What is the main reason for a cold start in Azure Functions?

easy

A. The app runs continuously without any breaks

B. The app starts from zero after a period of inactivity causing delay

C. The app uses a premium plan to stay warm

D. The app is deployed in multiple regions

Solution

1. Step 1: Understand cold start concept

   Cold start happens when an app is idle and then starts fresh, causing delay.

2. Step 2: Identify cause of delay

   The delay is due to the app starting from zero after inactivity, not continuous running or premium plans.

3. Final Answer:

   The app starts from zero after a period of inactivity causing delay -> Option B

4. Quick Check:

   Cold start = delay after inactivity [OK]

Hint: Cold start means delay after app inactivity [OK]

Common Mistakes:

• Confusing cold start with continuous running
• Thinking premium plans cause cold start
• Assuming multi-region deployment causes cold start

2. Which Azure plan helps avoid cold start delays by keeping apps warm?

easy

A. Consumption plan

B. Free plan

C. Basic plan

D. Premium plan

Solution

1. Step 1: Identify plan types

   Azure offers different plans: Consumption, Premium, Basic, Free.

2. Step 2: Match plan to cold start behavior

   Premium plan keeps apps warm to avoid cold start delays, unlike Consumption or Free plans.

3. Final Answer:

   Premium plan -> Option D

4. Quick Check:

   Premium plan = keeps apps warm [OK]

Hint: Premium plan avoids cold start by keeping app warm [OK]

Common Mistakes:

• Choosing Consumption plan which allows cold starts
• Confusing Basic plan with Premium
• Assuming Free plan prevents cold start

3. Consider this scenario: An Azure Function app on a Consumption plan is idle for hours. What happens when a new request arrives?

medium

A. The app experiences a cold start delay before responding

B. The app responds instantly with no delay

C. The app crashes due to inactivity

D. The app automatically switches to Premium plan

Solution

1. Step 1: Analyze Consumption plan behavior

   Consumption plan apps scale down to zero when idle, causing cold start on new requests.

2. Step 2: Predict app response on new request

   When a new request arrives after inactivity, the app must start fresh, causing delay.

3. Final Answer:

   The app experiences a cold start delay before responding -> Option A

4. Quick Check:

   Consumption plan + idle = cold start delay [OK]

Hint: Consumption plan apps cold start after idle [OK]

Common Mistakes:

• Assuming instant response on Consumption plan
• Thinking app crashes after inactivity
• Believing app auto-switches plans

4. You deployed an Azure Function on a Premium plan but still notice cold start delays. What is the most likely cause?

medium

A. The app is configured to scale to zero during inactivity

B. The app is using the Consumption plan instead

C. The app has too many instances running

D. The app is deployed in multiple regions

Solution

1. Step 1: Understand Premium plan behavior

   Premium plan keeps apps warm and avoids scaling to zero by default.

2. Step 2: Identify misconfiguration

   If cold start occurs, likely the app is configured to scale to zero despite Premium plan, causing cold start.

3. Final Answer:

   The app is configured to scale to zero during inactivity -> Option A

4. Quick Check:

   Scaling to zero causes cold start even on Premium [OK]

Hint: Check if scaling to zero is enabled on Premium plan [OK]

Common Mistakes:

• Assuming Premium plan never cold starts regardless of config
• Confusing Consumption plan usage
• Thinking multiple regions cause cold start

5. You want an Azure Function app to respond instantly even after long idle periods. Which combination best achieves this?

hard

A. Use Consumption plan with manual warm-up triggers

B. Use Free plan with auto-scaling enabled

C. Use Premium plan with Always On enabled

D. Use Basic plan with cold start optimization

Solution

1. Step 1: Identify plan for instant response

   Premium plan supports Always On feature to keep app warm and avoid cold start.

2. Step 2: Evaluate other options

   Consumption plan needs manual warm-up and may still cold start; Free and Basic plans lack Always On.

3. Final Answer:

   Use Premium plan with Always On enabled -> Option C

4. Quick Check:

   Premium + Always On = no cold start [OK]

Hint: Enable Always On in Premium plan for instant response [OK]

Common Mistakes:

• Relying on Consumption plan for instant response
• Assuming Free plan supports Always On
• Thinking Basic plan has cold start optimization