3.1 Azure Load Balancer and Traffic Manager
📘Microsoft Azure Networking Solutions (AZ-700)
Overview
Azure Load Balancer (ALB) is a Layer 4 (Transport Layer) service that distributes network traffic evenly across multiple resources, such as virtual machines (VMs), in Azure.
It ensures high availability and reliability for applications that need constant access. ALB works with TCP and UDP traffic, not with HTTP or HTTPS at Layer 7 (for that, Azure Application Gateway or Traffic Manager is used).
Key Features of Azure Load Balancer
- High availability – if one VM or resource goes down, traffic is automatically redirected to healthy VMs.
- Low latency – the distribution is fast, so user requests are served quickly.
- Scalability – you can add or remove VMs from the pool without downtime.
- Health probes – checks whether VMs or resources are healthy and only sends traffic to healthy ones.
- Layer 4 traffic support – works at network transport layer, handling TCP/UDP connections.
Types of Azure Load Balancer
- Public Load Balancer
- Exposes a public IP to the internet.
- Used when external clients need access to your service.
- Internal Load Balancer
- Used within a virtual network (VNet).
- Only accessible internally.
- Useful for backend services that shouldn’t be exposed publicly.
When to Use Azure Load Balancer (Use Cases)
Here are the common use cases you should remember for the AZ-700 exam, with IT examples:
1. High Availability for Multi-VM Applications
- Scenario: You have a web application hosted on 3 VMs.
- Use Case: Distribute incoming traffic across these VMs so if one VM fails, others continue serving users.
- IT Example: Web server farm, where each VM hosts a copy of your application.
2. Internal Traffic Distribution
- Scenario: Backend services like databases or APIs.
- Use Case: Use an internal load balancer to route traffic among multiple backend servers.
- IT Example: A set of database servers handling internal requests from an application tier.
3. UDP or TCP-Based Services
- Scenario: Applications that use TCP or UDP instead of HTTP/S protocols.
- Use Case: Azure Load Balancer can handle protocols like FTP, SSH, or gaming traffic.
- IT Example: Multiplayer game servers or DNS services using UDP.
4. Network-Level Failover
- Scenario: Some VMs may go down unexpectedly.
- Use Case: Azure Load Balancer uses health probes to detect unhealthy VMs and automatically reroute traffic to healthy VMs.
- IT Example: Any multi-tier application where uptime is critical, like a banking transaction system.
5. Scaling Applications
- Scenario: An application needs to serve more users than a single VM can handle.
- Use Case: Add more VMs to the backend pool. ALB automatically balances the load.
- IT Example: Auto-scaling an e-commerce website during a sale.
6. Low-Latency, High-Performance Applications
- Scenario: Applications require fast response times.
- Use Case: ALB distributes traffic efficiently, keeping latency minimal.
- IT Example: Real-time analytics services or chat applications.
Things Not Suitable for Azure Load Balancer
- ALB does not handle Layer 7 traffic (like HTTP routing based on URL paths).
- For features like SSL termination, session affinity at HTTP level, or content-based routing, Application Gateway or Traffic Manager is more appropriate.
- ALB works well for network-level load balancing only.
Exam Tips: Remember
- Azure Load Balancer = Layer 4, handles TCP/UDP.
- Public vs Internal:
- Public → Internet-facing applications
- Internal → Private VNet services
- Key features for use cases:
- Health probes
- Low latency
- High availability
- Scalability
- Ideal scenarios:
- Multi-VM applications
- Internal backend services
- TCP/UDP apps
- High-availability and failover setups
- Not for HTTP/HTTPS advanced routing (use App Gateway for that).
Summary Table for Quick Exam Recall
| Use Case | Load Balancer Type | IT Example |
|---|---|---|
| Public-facing app | Public LB | Web servers serving internet users |
| Internal traffic distribution | Internal LB | Backend API or DB servers |
| TCP/UDP service | Public/Internal LB | Multiplayer game server, DNS |
| High availability/failover | Any LB | Multi-tier applications, VMs in a pool |
| Scaling apps | Any LB | Auto-scaled web servers during traffic spikes |
