High availability design patterns in Azure - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

Understanding Azure Load Balancer behavior in HA setup

You deploy two virtual machines behind an Azure Load Balancer for high availability. One VM is healthy, the other is unhealthy. What will the Load Balancer do?

A It will send traffic to both VMs regardless of health status.

B It will send traffic only to the healthy VM and stop sending to the unhealthy one.

C It will stop sending traffic to both VMs until both are healthy.

D It will send traffic only to the unhealthy VM to try to recover it.

💡 Hint

Think about how load balancers maintain service availability by checking health probes.

Azure Load Balancer uses health probes to detect unhealthy VMs and routes traffic only to healthy instances to maintain availability.

❓ service_behavior

intermediate

Azure SQL Database failover behavior in HA configuration

You configure an Azure SQL Database with geo-replication for high availability. If the primary region fails, what happens to the database endpoint?

A The database endpoint switches to a read-only mode until manual intervention.

B The database endpoint remains pointing to the primary region and requires manual update.

C The database endpoint is deleted and must be recreated in the secondary region.

D The database endpoint automatically redirects to the secondary region after failover.

💡 Hint

Consider how geo-replication supports automatic failover to maintain availability.

Azure SQL Database geo-replication supports automatic failover where the endpoint redirects to the secondary region to maintain service continuity.

❓ security

advanced

Securing high availability Azure App Service with private endpoints

You want to secure your Azure App Service in a high availability setup by restricting access to only your virtual network. Which configuration achieves this?

A Use IP restrictions on the App Service to allow only your public IP addresses.

B Deploy the App Service in an isolated App Service Environment without private endpoints.

C Enable Private Endpoint for the App Service and integrate it with your virtual network.

D Configure a Network Security Group to block all inbound traffic to the App Service.

💡 Hint

Think about how private endpoints provide secure, private connectivity within a virtual network.

Private Endpoints allow Azure App Service to be accessed privately within a virtual network, enhancing security in HA setups.

✅ Best Practice

advanced

Designing multi-region high availability for Azure Storage accounts

Which Azure Storage redundancy option provides the highest availability and durability across regions?

A Geo-zone-redundant storage (GZRS)

B Locally-redundant storage (LRS)

C Read-access geo-redundant storage (RA-GRS)

D Zone-redundant storage (ZRS)

💡 Hint

Consider redundancy that combines zone and geo replication for maximum resilience.

GZRS replicates data across availability zones and regions, providing the highest availability and durability.

🧠 Conceptual

expert

Impact of Azure Traffic Manager routing methods on high availability

You configure Azure Traffic Manager with multiple endpoints in different regions. Which routing method ensures traffic is sent to the closest healthy endpoint to reduce latency and maintain availability?

A Performance routing method

B Priority routing method

C Weighted routing method

D Geographic routing method

💡 Hint

Think about routing methods that optimize for lowest network latency.

The Performance routing method directs traffic to the endpoint with the lowest network latency, improving availability and user experience.

Practice

1. Which Azure service is primarily used to distribute incoming traffic across multiple virtual machines to ensure high availability?

easy

A. Azure Functions

B. Azure Blob Storage

C. Azure Load Balancer

D. Azure Cosmos DB

Solution

1. Step 1: Understand the role of Azure Load Balancer

   Azure Load Balancer distributes incoming network traffic across multiple VMs to prevent any single VM from becoming a bottleneck.

2. Step 2: Compare with other services

   Azure Blob Storage stores data, Azure Functions run code, and Cosmos DB is a database service; none distribute traffic.

3. Final Answer:

   Azure Load Balancer -> Option C

4. Quick Check:

   Traffic distribution = Azure Load Balancer [OK]

Hint: Load Balancer spreads traffic to VMs for uptime [OK]

Common Mistakes:

• Confusing storage or compute services with traffic distribution
• Choosing Azure Functions for load balancing
• Selecting database services for availability patterns

2. Which of the following is the correct syntax to create an Azure VM Scale Set using Azure CLI for high availability?

easy

A. az vm create --name MyScaleSet --resource-group MyResourceGroup --image UbuntuLTS --instance-count 3

B. az vm create --name MyScaleSet --resource-group MyResourceGroup --image UbuntuLTS --count 3

C. az vmss deploy --name MyScaleSet --group MyResourceGroup --image UbuntuLTS --instances 3

D. az vmss create --name MyScaleSet --resource-group MyResourceGroup --image UbuntuLTS --instance-count 3

Solution

1. Step 1: Identify the correct Azure CLI command for VM Scale Set creation

   The command to create a VM Scale Set is az vmss create, not az vm create.

2. Step 2: Check the parameters

   Parameters like --name, --resource-group, --image, and --instance-count are correctly used in az vmss create --name MyScaleSet --resource-group MyResourceGroup --image UbuntuLTS --instance-count 3.

3. Final Answer:

   az vmss create --name MyScaleSet --resource-group MyResourceGroup --image UbuntuLTS --instance-count 3 -> Option D

4. Quick Check:

   VM Scale Set creation uses az vmss create [OK]

Hint: Use 'az vmss create' for VM Scale Sets [OK]

Common Mistakes:

• Using 'az vm create' instead of 'az vmss create'
• Incorrect parameter names like --count instead of --instance-count
• Mixing resource group parameter names

3. Consider this Azure Load Balancer configuration snippet:

frontendIPConfiguration:
  name: LoadBalancerFrontEnd
  publicIPAddress:
    id: /subscriptions/xxx/resourceGroups/rg/providers/Microsoft.Network/publicIPAddresses/myPublicIP
backendAddressPools:
  - name: BackendPool
loadBalancingRules:
  - name: HTTPRule
    frontendIPConfiguration: LoadBalancerFrontEnd
    backendAddressPool: BackendPool
    protocol: Tcp
    frontendPort: 80
    backendPort: 80
    enableFloatingIP: false
    idleTimeoutInMinutes: 4
    loadDistribution: Default

What will happen if one VM in the backend pool becomes unhealthy?

medium

A. Traffic will automatically stop going to the unhealthy VM

B. Traffic will continue to be sent to the unhealthy VM

C. Load Balancer will restart the unhealthy VM

D. Load Balancer will redirect traffic to a different port

Solution

1. Step 1: Understand Azure Load Balancer health probe behavior

   Azure Load Balancer requires health probes configured to detect unhealthy VMs and stop sending traffic to them. This snippet does not show health probes configured, but in practice, health probes are necessary for proper load balancing.

2. Step 2: Analyze the effect of missing health probes

   Without health probes, the Load Balancer cannot detect unhealthy VMs, so it continues sending traffic to all VMs in the backend pool. However, best practice is to configure health probes to avoid this.

3. Final Answer:

   Traffic will automatically stop going to the unhealthy VM -> Option A

4. Quick Check:

   Health probes detect unhealthy VMs and stop traffic [OK]

Hint: Configure health probes to avoid sending traffic to bad VMs [OK]

Common Mistakes:

• Assuming Load Balancer auto-detects unhealthy VMs without probes
• Thinking Load Balancer restarts VMs
• Confusing port redirection with load balancing

4. You have configured an Active-Passive high availability setup using Azure Traffic Manager. However, during failover, users experience downtime. What is the most likely cause?

medium

A. Traffic Manager is set to Performance routing with multiple active endpoints

B. Traffic Manager is set to Priority routing but health probes are misconfigured

C. Azure Load Balancer is not configured with a public IP

D. VM Scale Set has only one instance

Solution

1. Step 1: Understand Active-Passive with Traffic Manager Priority routing

   Priority routing sends traffic to the primary endpoint unless it is unhealthy, then fails over to secondary.

2. Step 2: Identify impact of misconfigured health probes

   If health probes are misconfigured, Traffic Manager cannot detect endpoint health and will not failover properly, causing downtime.

3. Final Answer:

   Traffic Manager is set to Priority routing but health probes are misconfigured -> Option B

4. Quick Check:

   Priority routing + bad probes = failover fails [OK]

Hint: Check health probes when failover fails in Priority routing [OK]

Common Mistakes:

• Confusing routing methods in Traffic Manager
• Blaming Load Balancer or VM Scale Set for Traffic Manager failover
• Ignoring health probe configuration

5. You want to design a geo-redundant high availability solution for a web app in Azure that must remain available even if an entire Azure region fails. Which combination of Azure services and design patterns best achieves this?

hard

A. Deploy the app in two regions with Azure Traffic Manager using Performance routing and Azure SQL Geo-Replication

B. Deploy the app in one region with Azure Load Balancer and VM Scale Sets, and use Azure Backup for disaster recovery

C. Deploy the app in two regions with Azure Traffic Manager using Priority routing and VM Scale Sets in each region

D. Deploy the app in one region with Azure Application Gateway and use Azure Blob Storage for static content

Solution

1. Step 1: Understand geo-redundancy requirements

   To survive a full region failure, the app must be deployed in multiple regions with traffic routed between them.

2. Step 2: Evaluate options for traffic routing and data replication

   Performance routing in Traffic Manager directs users to the closest healthy region. Azure SQL Geo-Replication ensures database availability across regions.

3. Step 3: Compare with other options

   Priority routing is for Active-Passive, not best for geo-load balancing. Single region deployments cannot survive region failure. Application Gateway is regional and does not provide geo-failover.

4. Final Answer:

   Deploy the app in two regions with Azure Traffic Manager using Performance routing and Azure SQL Geo-Replication -> Option A

5. Quick Check:

   Geo-redundancy needs multi-region + performance routing + geo-replication [OK]

Hint: Use multi-region + Traffic Manager Performance + Geo-Replication [OK]

Common Mistakes:

• Choosing Priority routing for geo-load balancing
• Relying on single region with backup for high availability
• Confusing Application Gateway with global traffic routing