Managed instance groups in GCP - Mini Project: Build & Apply

Create a Managed Instance Group on Google Cloud

📖 Scenario: You are setting up a scalable web application on Google Cloud. To handle traffic efficiently, you want to create a group of virtual machines that can automatically grow or shrink based on demand.

🎯 Goal: Build a Managed Instance Group (MIG) using Google Cloud CLI commands that launches multiple instances from a template and can scale automatically.

📋 What You'll Learn

Create an instance template named web-template with a Debian image

Create a managed instance group named web-mig in the us-central1-a zone using the web-template

Set the initial size of the managed instance group to 2 instances

Configure autoscaling for the managed instance group to scale between 2 and 5 instances based on CPU utilization at 60%

💡 Why This Matters

🌍 Real World

Managed instance groups help run applications that need to handle changing traffic by automatically adding or removing virtual machines.

💼 Career

Cloud engineers and DevOps professionals use managed instance groups to ensure applications are scalable, reliable, and cost-efficient.

1

Create an instance template

Use the gcloud command to create an instance template named web-template with the Debian 11 image.

GCP

# Use gcloud to create an instance template named web-template with Debian 11
# Your code here

Hint

Use gcloud compute instance-templates create with --image-family=debian-11 and --image-project=debian-cloud.

2

Create a managed instance group

Create a managed instance group named web-mig in the us-central1-a zone using the instance template web-template and set the size to 2.

GCP

gcloud compute instance-templates create web-template --machine-type=e2-small --image-family=debian-11 --image-project=debian-cloud
# Create a managed instance group named web-mig in us-central1-a with size 2 using web-template
# Your code here

Hint

Use gcloud compute instance-groups managed create with --size 2, --template web-template, and --zone us-central1-a.

3

Configure autoscaling for the managed instance group

Set autoscaling on the managed instance group web-mig in us-central1-a to scale between 2 and 5 instances based on CPU utilization at 60%.

GCP

gcloud compute instance-templates create web-template --machine-type=e2-small --image-family=debian-11 --image-project=debian-cloud
gcloud compute instance-groups managed create web-mig --base-instance-name web-instance --size 2 --template web-template --zone us-central1-a
# Configure autoscaling for web-mig to scale between 2 and 5 instances at 60% CPU utilization
# Your code here

Hint

Use gcloud compute instance-groups managed set-autoscaling with the correct flags for min, max replicas and CPU utilization.

4

Verify the managed instance group configuration

Add the command to describe the managed instance group web-mig in us-central1-a to check its configuration.

GCP

gcloud compute instance-templates create web-template --machine-type=e2-small --image-family=debian-11 --image-project=debian-cloud
gcloud compute instance-groups managed create web-mig --base-instance-name web-instance --size 2 --template web-template --zone us-central1-a
gcloud compute instance-groups managed set-autoscaling web-mig --max-num-replicas 5 --min-num-replicas 2 --target-cpu-utilization 0.6 --zone us-central1-a
# Describe the managed instance group web-mig in us-central1-a to verify configuration
# Your code here

Hint

Use gcloud compute instance-groups managed describe with the group name and zone.

Practice

1. What is the main purpose of a Managed Instance Group (MIG) in Google Cloud?

easy

A. To create a single virtual machine with custom settings

B. To run multiple copies of the same virtual machine for reliability

C. To store large amounts of data in the cloud

D. To manage user access and permissions

Solution

1. Step 1: Understand the role of Managed Instance Groups

   Managed Instance Groups run many copies of the same VM to keep applications reliable and available.

2. Step 2: Compare options with this role

   Options describing storage, single VM creation, and permissions are other cloud services, not MIGs.

3. Final Answer:

   To run multiple copies of the same virtual machine for reliability -> Option B

4. Quick Check:

   MIGs = multiple VM copies for reliability [OK]

Hint: MIGs run many identical VMs to keep apps running [OK]

Common Mistakes:

• Confusing MIGs with storage services
• Thinking MIGs manage single VMs only
• Mixing up MIGs with user permission management

2. Which command correctly creates a managed instance group named web-group with 3 instances using the instance template web-template?

easy

A. gcloud compute instance-groups managed create web-group --template=web-template --size=3

B. gcloud compute instance-groups create web-group --template web-template --count 3

C. gcloud compute managed-instances create web-group --template=web-template --size=3

D. gcloud compute instance-groups managed create web-group --template web-template --count=3

Solution

1. Step 1: Identify correct gcloud syntax for managed instance group creation

   The correct command uses 'gcloud compute instance-groups managed create' with '--template' and '--size' flags.

2. Step 2: Check each option for syntax correctness

   gcloud compute instance-groups managed create web-group --template=web-template --size=3 matches the correct syntax exactly. The other options have incorrect flags or command structure.

3. Final Answer:

   gcloud compute instance-groups managed create web-group --template=web-template --size=3 -> Option A

4. Quick Check:

   Correct command syntax = gcloud compute instance-groups managed create web-group --template=web-template --size=3 [OK]

Hint: Use '--template' and '--size' with 'instance-groups managed create' [OK]

Common Mistakes:

• Using 'count' instead of 'size'
• Omitting 'managed' keyword
• Wrong command order or flags

3. Given this autoscaling policy for a managed instance group:

autoscaling:
  minNumReplicas: 2
  maxNumReplicas: 5
  cpuUtilization:
    targetUtilization: 0.6

What happens when CPU usage rises to 80%?

medium

A. The group stays at the current number of instances

B. The group scales down to 2 instances

C. The group scales up by adding more instances, up to 5

D. The group deletes all instances

Solution

1. Step 1: Understand autoscaling triggers

   The target CPU utilization is 60%. When actual CPU usage is 80%, it is above the target.

2. Step 2: Determine autoscaling behavior

   Since CPU usage is higher than target, autoscaler adds instances up to maxNumReplicas (5) to reduce load.

3. Final Answer:

   The group scales up by adding more instances, up to 5 -> Option C

4. Quick Check:

   CPU > target -> scale up [OK]

Hint: CPU above target means add instances [OK]

Common Mistakes:

• Thinking it scales down when CPU is high
• Assuming no change happens
• Confusing min and max replica counts

4. You try to update a managed instance group with a new instance template but get an error. Which is the most likely cause?

medium

A. Autoscaling is disabled

B. You did not specify the rolling update policy

C. The managed instance group has zero instances

D. The instance template name is missing or incorrect

Solution

1. Step 1: Identify common update errors

   Updating a MIG requires a valid instance template name; missing or wrong name causes errors.

2. Step 2: Evaluate other options

   Rolling update policy is optional, zero instances or autoscaling off do not cause update errors.

3. Final Answer:

   The instance template name is missing or incorrect -> Option D

4. Quick Check:

   Invalid template name -> update error [OK]

Hint: Check instance template name carefully when updating MIG [OK]

Common Mistakes:

• Assuming rolling update policy is mandatory
• Ignoring template name correctness
• Confusing autoscaling with update errors

5. You want to ensure zero downtime when updating a managed instance group with a new version of your app. Which strategy should you use?

hard

A. Perform a rolling update with a minimal number of instances unavailable at once

B. Delete all instances and recreate them with the new template immediately

C. Turn off autoscaling before updating and turn it back on after

D. Manually stop each instance, update it, then start it again

Solution

1. Step 1: Understand zero downtime update methods

   Rolling updates replace instances gradually, keeping most instances running to avoid downtime.

2. Step 2: Evaluate other options for downtime risk

   Deleting all instances or manual stop/start causes downtime; turning off autoscaling is unrelated.

3. Final Answer:

   Perform a rolling update with a minimal number of instances unavailable at once -> Option A

4. Quick Check:

   Rolling update = zero downtime [OK]

Hint: Use rolling updates to avoid downtime during MIG changes [OK]

Common Mistakes:

• Deleting all instances at once
• Manual updates causing downtime
• Misunderstanding autoscaling role in updates