Managed instance groups in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

How does a Managed Instance Group handle instance updates?

You have a Managed Instance Group (MIG) with 5 instances running a web application. You want to update the application version on all instances with minimal downtime.

Which behavior best describes how the MIG handles rolling updates?

A It deletes all instances and creates new ones with the updated version at the same time.

B It updates all instances simultaneously, causing downtime during the update.

C It updates instances one at a time, ensuring some instances remain available during the update.

D It requires manual deletion of instances before creating updated ones.

💡 Hint

Think about how to keep the service available during updates.

MIGs perform rolling updates by updating instances one at a time or in small batches. This approach keeps some instances running to serve traffic, minimizing downtime.

❓ service_behavior

intermediate

What happens when an instance in a Managed Instance Group becomes unhealthy?

You have a Managed Instance Group with health checks configured. One instance fails the health check.

What does the Managed Instance Group do automatically?

A It marks the instance as unhealthy and recreates it after a grace period.

B It ignores the unhealthy instance and continues running it.

C It stops the instance but does not replace it automatically.

D It immediately deletes the unhealthy instance and creates a new one.

💡 Hint

Consider how MIGs maintain the desired number of healthy instances.

MIGs mark instances as unhealthy when they fail health checks and recreate them after a grace period to maintain the target size and health.

❓ security

advanced

Which IAM role is required to create and manage Managed Instance Groups securely?

You want to grant a team member permissions to create and manage Managed Instance Groups without giving full project access.

Which IAM role should you assign?

A roles/compute.instanceAdmin.v1

B roles/compute.instanceGroupManager

C roles/compute.networkAdmin

D roles/owner

💡 Hint

Look for the role specific to Managed Instance Groups.

The role roles/compute.instanceGroupManager grants permissions to create and manage Managed Instance Groups without broader project permissions.

❓ Configuration

advanced

What is the effect of setting the 'autohealing' policy in a Managed Instance Group?

You configure an autohealing policy with a health check on a Managed Instance Group.

What happens when an instance fails the health check under this policy?

A The instance is automatically recreated to replace the unhealthy one.

B The instance is stopped but not replaced automatically.

C The instance continues running despite failing the health check.

D The entire Managed Instance Group is deleted and recreated.

💡 Hint

Think about how autohealing maintains instance health.

Autohealing automatically recreates instances that fail health checks to maintain group health and availability.

✅ Best Practice

expert

How should you configure a Managed Instance Group to handle sudden traffic spikes efficiently?

You expect sudden increases in traffic to your application. You want the Managed Instance Group to add instances quickly but avoid excessive costs.

Which configuration best achieves this?

A Set a high fixed number of instances to handle peak traffic at all times.

B Manually add instances when traffic increases and remove them when it decreases.

C Disable autoscaling and rely on load balancer to distribute traffic.

D Use autoscaling based on CPU utilization with a maximum instance limit and cooldown period.

💡 Hint

Consider balancing responsiveness and cost control.

Autoscaling based on CPU utilization with limits and cooldowns allows the group to scale up quickly during spikes and scale down to save costs.

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