High availability configuration in GCP - Mini Project: Build & Apply

High availability configuration

📖 Scenario: You are setting up a simple web application on Google Cloud Platform (GCP). To ensure your application is always available, even if one server fails, you want to configure a high availability setup.This means your app will run on multiple virtual machines, and traffic will be balanced between them automatically.

🎯 Goal: Build a high availability configuration on GCP by creating an instance template, a managed instance group with multiple instances, and a load balancer to distribute traffic.

📋 What You'll Learn

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

Create a managed instance group named web-mig in the us-central1-a zone using the instance template with 2 instances

Create a HTTP load balancer forwarding rule named web-lb that balances traffic to the managed instance group

💡 Why This Matters

🌍 Real World

High availability ensures that web applications stay online even if some servers fail. This setup is common for websites and services that need to be reliable.

💼 Career

Cloud engineers and DevOps professionals often configure managed instance groups and load balancers to build scalable and fault-tolerant applications.

1

Create an instance template

Create an instance template called web-instance-template using the Debian 11 image from the debian-cloud project.

GCP

# Your code here to create the instance template named web-instance-template

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 zone us-central1-a using the instance template web-instance-template with 2 instances.

GCP

gcloud compute instance-templates create web-instance-template \
  --image-family=debian-11 \
  --image-project=debian-cloud
# Your code here to create the managed instance group named web-mig

Hint

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

3

Create a backend service and health check

Create a health check named web-health-check and a backend service named web-backend-service that uses the health check and points to the managed instance group web-mig in zone us-central1-a.

GCP

gcloud compute instance-templates create web-instance-template \
  --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-instance-template \
  --zone us-central1-a
# Your code here to create health check and backend service

Hint

Create a health check with gcloud compute health-checks create http web-health-check --port 80. Then create a backend service with gcloud compute backend-services create web-backend-service --protocol HTTP --health-checks web-health-check --global. Finally, add the instance group as backend with gcloud compute backend-services add-backend.

4

Create a HTTP load balancer forwarding rule

Create a URL map named web-url-map, a target HTTP proxy named web-http-proxy, and a global forwarding rule named web-lb that listens on port 80 and forwards traffic to the backend service web-backend-service.

GCP

gcloud compute instance-templates create web-instance-template \
  --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-instance-template \
  --zone us-central1-a

gcloud compute health-checks create http web-health-check --port 80

gcloud compute backend-services create web-backend-service --protocol HTTP --health-checks web-health-check --global

gcloud compute backend-services add-backend web-backend-service --instance-group web-mig --instance-group-zone us-central1-a --global
# Your code here to create the URL map, target proxy, and forwarding rule named web-lb

Hint

Create URL map: gcloud compute url-maps create web-url-map --default-service web-backend-service --global
Create target proxy: gcloud compute target-http-proxies create web-http-proxy --url-map web-url-map --global
Create forwarding rule: gcloud compute forwarding-rules create web-lb --global --ports=80 --target-http-proxy web-http-proxy.

Practice

1. What is the main purpose of configuring high availability in a cloud service?

easy

A. To make the service run faster for a single user

B. To reduce the cost of running the service

C. To limit the number of users accessing the service

D. To keep the service running even if some parts fail

Solution

1. Step 1: Understand high availability concept

   High availability means the system stays up and working even if some components fail.

2. Step 2: Identify the main goal

   The goal is to avoid downtime and keep the service accessible to users.

3. Final Answer:

   To keep the service running even if some parts fail -> Option D

4. Quick Check:

   High availability = service stays running despite failures [OK]

Hint: High availability means no downtime during failures [OK]

Common Mistakes:

• Confusing high availability with cost reduction
• Thinking it only improves speed for one user
• Assuming it limits user access

2. Which GCP resource helps automatically replace unhealthy VM instances to maintain high availability?

easy

A. Managed Instance Group with health checks

B. Cloud Storage Bucket

C. Cloud SQL instance

D. Cloud Functions

Solution

1. Step 1: Identify resource for auto healing

   Managed Instance Groups (MIGs) can use health checks to detect unhealthy VMs.

2. Step 2: Understand auto replacement

   MIGs automatically recreate unhealthy instances to keep the service healthy.

3. Final Answer:

   Managed Instance Group with health checks -> Option A

4. Quick Check:

   Auto replace unhealthy VMs = Managed Instance Group + health checks [OK]

Hint: Auto healing uses Managed Instance Groups with health checks [OK]

Common Mistakes:

• Choosing storage or database services instead of compute
• Confusing Cloud Functions with VM management
• Ignoring health checks role

3. Consider a Managed Instance Group spread across two zones with health checks enabled. If one zone fails completely, what happens to the instances?

medium

A. Instances in the failed zone are replaced in the same zone

B. Instances in the failed zone remain down until manual restart

C. Instances in the failed zone are replaced in the other zone

D. All instances in both zones are shut down

Solution

1. Step 1: Understand multi-zone MIG behavior

   MIGs spread instances across zones for fault tolerance.

2. Step 2: Analyze failure impact

   If one zone fails, MIG recreates instances in healthy zones to maintain capacity.

3. Final Answer:

   Instances in the failed zone are replaced in the other zone -> Option C

4. Quick Check:

   Zone failure triggers instance replacement in healthy zones [OK]

Hint: MIGs replace failed zone instances in other zones automatically [OK]

Common Mistakes:

• Thinking instances are replaced in the failed zone
• Assuming manual restart is needed
• Believing all instances shut down

4. You configured a Managed Instance Group with health checks, but unhealthy instances are not being replaced. What is the most likely cause?

medium

A. Autohealing is disabled in the instance group

B. Instances are in multiple zones

C. Health check is not attached to the instance group

D. Firewall rules block all traffic

Solution

1. Step 1: Check health check attachment

   Health checks must be attached to trigger autohealing, but this alone is not enough.

2. Step 2: Verify autohealing setting

   Autohealing must be enabled in the instance group to replace unhealthy instances.

3. Final Answer:

   Autohealing is disabled in the instance group -> Option A

4. Quick Check:

   Autohealing disabled = no instance replacement [OK]

Hint: Autohealing must be enabled to replace unhealthy instances [OK]

Common Mistakes:

• Assuming health check attachment alone triggers replacement
• Blaming multi-zone setup
• Ignoring autohealing configuration

5. You want to design a highly available web application on GCP that remains online even if an entire zone fails. Which combination of configurations best achieves this?

hard

A. Single-zone Managed Instance Group with health checks and autoscaling

B. Multi-zone Managed Instance Group with health checks and autoscaling

C. Single VM instance with a static IP and firewall rules

D. Cloud Storage bucket with versioning enabled

Solution

1. Step 1: Understand zone failure impact

   A single zone failure can take down all instances in that zone if only single-zone is used.

2. Step 2: Choose multi-zone MIG with health checks and autoscaling

   This setup spreads instances across zones, replaces unhealthy ones, and adjusts capacity automatically.

3. Step 3: Evaluate other options

   Single-zone lacks zone failure protection; single VM is a single point of failure; storage bucket is not compute.

4. Final Answer:

   Multi-zone Managed Instance Group with health checks and autoscaling -> Option B

5. Quick Check:

   Multi-zone MIG + health checks + autoscaling = high availability [OK]

Hint: Use multi-zone MIG with health checks and autoscaling for best availability [OK]

Common Mistakes:

• Choosing single-zone MIG ignoring zone failure
• Using single VM which is a single failure point
• Confusing storage bucket with compute resources