Managed instance groups in GCP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Managed Instance Group (MIG) in Google Cloud?

A Managed Instance Group is a collection of virtual machine instances that are managed as a single entity. It automatically handles tasks like scaling, updating, and healing instances to keep your application running smoothly.

beginner

How does a Managed Instance Group handle scaling?

A Managed Instance Group can automatically add or remove VM instances based on load or schedule. This helps your application handle more users or save costs when demand is low.

intermediate

What is the difference between a zonal and regional Managed Instance Group?

A zonal MIG manages instances in a single zone, while a regional MIG spreads instances across multiple zones in a region. Regional MIGs provide higher availability by distributing instances.

intermediate

What does 'autohealing' mean in the context of Managed Instance Groups?

Autohealing means the MIG automatically detects unhealthy instances and replaces them with new, healthy ones to keep your service running without manual intervention.

beginner

Why should you use instance templates with Managed Instance Groups?

Instance templates define the configuration for VM instances in a MIG, like machine type and startup scripts. Using templates ensures all instances are consistent and makes updates easier.

What is the main benefit of using a Managed Instance Group?

A Requires manual updates for each instance

B Manual control of each VM instance

C Only works with one VM instance

D Automatic scaling and healing of VM instances

Managed Instance Groups automatically scale and heal VM instances to maintain application availability.

Which type of Managed Instance Group provides higher availability by spreading instances across zones?

A Regional Managed Instance Group

B Zonal Managed Instance Group

C Single-instance Group

D Unmanaged Instance Group

Regional Managed Instance Groups distribute instances across multiple zones to improve availability.

What is the purpose of an instance template in a Managed Instance Group?

A To manually start instances

B To store data for the instances

C To define the configuration for VM instances

D To monitor network traffic

Instance templates specify the settings for VM instances in a MIG, ensuring consistency.

What does autohealing do in a Managed Instance Group?

A Saves instance data to disk

B Automatically replaces unhealthy instances

C Stops all instances when unhealthy

D Manually restarts instances

Autohealing detects and replaces unhealthy instances automatically.

How does a Managed Instance Group help with cost management?

A By automatically scaling down instances when demand is low

B By charging a fixed monthly fee

C By requiring manual instance shutdown

D By limiting the number of users

MIGs can scale down instances automatically to save costs when demand decreases.

Explain how Managed Instance Groups improve application availability and reliability.

Think about how the group manages instances to keep the app running smoothly.

Describe the role of instance templates in Managed Instance Groups and why they are important.

Consider how templates help manage many instances at once.

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