In Azure, load balancing refers to the distribution of traffic across multiple servers. This is crucial in ensuring availability and reliability by redirecting requests from a malfunctioning server to a functioning one, a concept known as failover.
Azure offers two types of load balancing: Azure Load Balancer for managing layer-4 traffic (TCP, UDP), and Azure Application Gateway for managing layer-7 (HTTP/HTTPS) traffic.
Azure Load Balancer supports inbound and outbound scenarios, providing low latency and high throughput. It operates at the transport layer (Layer 4 in the OSI network model). The Azure Application Gateway offers more advanced features, such as SSL termination, cookie-based session affinity, and URL-based routing functionalities.
Post 2: Common Issues with Azure Load Balancing
Troubleshooting load balancing issues in Azure often involves looking at common problems such as:
- Problems with Health Probes: Azure uses health probes to determine the status of the backend instances. If an instance does not respond to a health probe, Azure considers it as “unhealthy” and does not route traffic to it.
- Load Balancer Configuration: Incorrect configurations are a common problem in load balancing.
- Backend Pool Management: If instances are not correctly added or removed from the backend pool, it can lead to traffic imbalance.
- Issues with Network Security Group (NSG) Rules: Misconfigured NSG rules may inadvertently block health probes or essential traffic which can disrupt load balancing.
Post 3: Azure Load Balancing – Best Practices
Use these guidelines for effective load balancing in Azure:
- Always ensure that your health probes are configured correctly. Use TCP or HTTP probes as per the requirement of your application.
- Configuration settings, like load balancing rules and backend pools need to be managed and updated carefully.
- NSG rules should allow health probe and necessary traffic to pass through for maintaining the flow of network traffic.
- Regularly monitoring and logging your traffic flow can help anticipate issues and maintain the balance effectively.
Post 4: Walkthrough for Troubleshooting Load Balancing
Let us consider an issue where an instance is removed from load balance rotation due to failing health probes.
First, verify the status of the health probe using the Get-AzLoadBalancer cmdlet. If you observe that the instance is “unhealthy”, investigate the application and server logs for potential issues.
Second, check the Load Balancer configuration for any rules that might be causing the instance to fail health checks. Also, verify the instances’ network security group (NSG) rules for any restrictions that might be blocking the health probe.
Following a systematic approach will be fruitful in troubleshooting your Azure load balancing issues.
Thus, the process of troubleshooting Azure load balancing demands a good understanding of your application architecture, as well as its interaction with the infrastructure. Regular monitoring and carefully managed configurations can help ensure a seamless, balanced load distribution in your applications.
Practice Test
True or False: Azure Load Balancer operates at the transport layer (Layer 4 in the OSI model).
- True
- False
Answer: True.
Explanation: Azure Load Balancer is a Layer 4 (TCP, UDP) load balancer that distributes incoming traffic among healthy instances of services defined in a load-balanced set.
What is the Azure service that provides automatic reconfiguration of IP addresses upon failure?
- A. Virtual Network Gateway
- B. Azure DNS
- C. Traffic Manager
- D. Azure Load Balancer
Answer: D. Azure Load Balancer.
Explanation: Azure Load Balancer can provide automatic reconfiguration of IP addresses upon failure, enabling high availability and reliability.
True or False: Azure Load Balancer can only distribute traffic within a single region.
- True
- False
Answer: False.
Explanation: Although an Azure Load Balancer works within a single region, Traffic Manager can manage traffic distribution across regions.
What does the Azure Load Balancer use to ensure high availability and reliability?
- A. Health probes
- B. Service Monitoring
- C. Network Security Groups
- D. Diagnostic Settings
Answer: A. Health probes.
Explanation: Health probes monitor the health of the instances and only distribute traffic to healthy instances.
True or False: Azure Standard Load Balancer supports both Internet and VNet traffic.
- True
- False
Answer: True.
Explanation: Azure Standard Load Balancer supports both inbound and outbound scenarios, provides low latency and high throughput, and scales up to millions of flows for all TCP and UDP applications.
What kind of troubleshooting can be done using Azure Network Watcher?
- A. VM health
- B. Storage account activity
- C. Network communication
- D. DNS resolution
Answer: C. Network communication
Explanation: Azure Network Watcher provides tools to monitor, diagnose, view metrics, and enable or disable logs for resources in an Azure virtual network.
True or False: You can’t use the Azure portal, Azure CLI, or PowerShell to troubleshoot Azure Load Balancer.
- True
- False
Answer: False.
Explanation: Azure Load Balancer can be troubleshooted through various means such as the Azure portal, Azure CLI, and PowerShell.
Which Azure service is best for managing user web traffic across globally distributed Web Apps?
- A. Traffic Manager
- B. Load Balancer
- C. Application Gateway
- D. Network Watcher
Answer: A. Traffic Manager
Explanation: Azure Traffic Manager allows you to control the distribution of user traffic for service endpoints in different datacenters, providing a range of traffic-routing methods and endpoints monitoring.
True or False: Network Security Group is used for distributing network traffic.
- True
- False
Answer: False.
Explanation: Network Security Group is used for filtering network traffic. Azure Load Balancer is used for distributing network traffic.
What are some common causes of load balancing issues in Azure?
- A. Configuration errors
- B. VM overload
- C. Network Security Group Rules
- D. All of the above
Answer: D. All of the above
Explanation: All these factors can influence the functionality of Load Balancer in Azure.
Interview Questions
What is the role of the Azure Load Balancer in the Azure Infrastructure?
The Azure Load Balancer distributes the inbound network traffic across multiple virtual machines and ensures high availability and reliability via network redundancy.
What are the two types of Azure load balancers?
Azure provides two types of load balancers – Internal and Public. The Public Load Balancer provides outbound connections for virtual machines (VMs) inside the network and inbound traffic for specific VMs. The Internal Load Balancer provides load balancing for VMs communicating among themselves within a VNet.
What type of distribution algorithm does Azure Load Balancer use?
Azure Load Balancer uses a 5 tuple (source IP, source port, destination IP, destination port, and protocol type) hash to distribute incoming traffic across multiple servers.
What should you check if the Azure load balancer is not distributing traffic evenly among the VMs?
If the Azure load balancer is not distributing traffic evenly among the VMs, check if the VMs are returning a health probe response. The Load balancer will only distribute traffic to a VM if it returns a successful health probe response under the configured conditions.
What is the purpose of a Health Probe in Azure Load Balancer?
Health Probes in Azure Load Balancer check the availability of the VM instances. If a VM doesn’t respond to the Health Probe as expected, the Load Balancer stops sending traffic to the problematic VM until it starts responding correctly.
What can be the possible issues if a VM in Azure is unable to connect with Load Balancer?
A VM might be unable to connect to the Load Balancer if it is not in a correct state or if there is a configuration mismatch in Load Balancer rules or health probes.
What is meant by “session persistence” in the context of Azure Load Balancer?
Session persistence in Azure Load Balancer is a setting that allows all traffic from a client IP to be directed to the same VM during a session. Useful in scenarios where the state of the client matters.
What is a back-end pool in Azure Load Balancer?
Back-end pool contains the IP addresses of the virtual (network) interfaces (NICs) connected to the Load Balancer.
What are the support protocols of the Azure Load Balancer?
Azure Load Balancer supports both TCP and UDP protocols.
If a VM is not receiving the traffic, what can be the possible reasons?
Possible reasons can include the VM being stopped or deallocated, firewall blocking the incoming traffic, health probe failure, or no matching Load Balancer rule for the incoming traffic.
What is the use of QoS (Quality of Service) in Azure Load Balancer?
Azure Load Balancer allows you to configure QoS. QoS ensures that certain types of network traffic get priority over others. This helps with efficient resource utilization and ensures high quality of service.
Can you load balance UDP traffic using Azure Load Balancer?
Yes, Azure Load Balancer supports both TCP and UDP protocol loads.
How can you troubleshoot an Azure Load Balancer?
Azure Load Balancer can be troubleshooted by using the Azure portal, using Network Watcher’s IP flow verify or Next hop, PowerShell or CLI.
Can session persistence setting be changed once the Azure Load Balancer is deployed?
Yes, session persistence can be changed after deployment. It can be set to “None”, “Client IP”, or “Client IP and Protocol”.
What is the maximum limit of Inbound NAT rules per Azure Load Balancer?
The Azure Load Balancer supports up to 150 Inbound NAT rules.
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