3.1 Azure Load Balancer and Traffic Manager
📘Microsoft Azure Networking Solutions (AZ-700)
1. Types of Azure Load Balancers
Azure provides two main types of load balancers:
- Basic Load Balancer
- Supports up to 300 instances.
- Limited to single availability set or virtual network.
- Fewer features, such as no zone-redundancy or diagnostic metrics.
- Use case: Simple internal applications or test environments.
- Standard Load Balancer
- Supports more than 1000 instances.
- Works across availability zones.
- Provides health probes, metrics, and security features.
- Supports static public IP addresses.
- Use case: Production workloads, high availability, large-scale apps.
Exam Tip: Always check if your scenario mentions “high availability,” “zone-redundancy,” or “production-grade” → use Standard LB. If it’s just dev/test → Basic LB.
2. SKU Choices (Basic vs Standard) Based on Requirements
| Requirement | Feature Needed | ALB Feature |
|---|---|---|
| Internal traffic only | Private IP inside VNet | Internal Load Balancer (ILB) |
| Public-facing apps | Users from internet | Public Load Balancer |
| Zone-redundancy | High SLA | Standard LB with Availability Zones |
| Static IP | Consistent IP for DNS | Standard LB with static IP |
| Many backend VMs | Scale | Standard LB |
| Simpler test app | Less traffic, fewer features | Basic LB |
Key Point: SKU + Type = match requirements.
3. Load Balancing Rules
These are used to map incoming traffic to backend VMs.
- Scenario: You have a web app running on 3 VMs in a VNet. Users connect to a public IP, and traffic should distribute evenly.
- Feature: ALB rule defines:
- Frontend IP (public/private)
- Backend pool (the 3 VMs)
- Protocol & port (HTTP/80 or TCP/443)
- Session persistence (keep a user on the same VM if needed)
Session persistence types:
- None – default; requests can go to any VM.
- Client IP – all requests from the same client IP go to same VM.
- Client IP + Protocol – more granular stickiness for multi-protocol apps.
4. Health Probes
- ALB checks the status of backend VMs.
- If a VM is unhealthy, it stops sending traffic there.
- Probe types: HTTP, TCP, or HTTPS.
- Scenario: Your API VM crashes. ALB detects it and stops sending traffic until it recovers.
- Exam Tip: If requirement mentions “traffic should go only to healthy instances,” the answer involves health probes.
5. Outbound and Inbound Rules
- Inbound: Traffic coming to your app → use load balancing rules.
- Outbound: Traffic from backend VMs to internet:
- Only Standard LB provides automatic SNAT (Source NAT) for outbound connections.
- Basic LB requires NAT rules for outbound.
Scenario: Backend VMs need to access a public API → map requirement to Standard LB outbound connectivity.
6. Availability Zones and High Availability
- Requirement: SLA ≥ 99.99%, survive a datacenter failure.
- Feature: Zone-redundant Standard Load Balancer.
- Basic LB cannot handle multiple zones.
- Exam questions often describe high availability scenarios → Standard LB with zones is the answer.
7. Backend Pool Types
- Backend pool can include:
- Virtual machines (VMs)
- VM scale sets
- Availability sets
- Scenario: You need auto-scaling → use VM scale sets in backend pool.
8. Network Security Integration
- Standard LB can integrate with Azure Firewall or NSGs for more secure traffic.
- Requirement: Only allow certain traffic → use Standard LB + NSG.
9. Key Mapping Checklist for the Exam
When you see a requirement in the exam, ask:
- Is it public or internal traffic?
- Does it need high availability / zones?
- How many backend instances/VMs?
- Do you need session persistence?
- Should it only route traffic to healthy instances?
- Is outbound connectivity required?
- Do you need static IP?
Mapping this helps you choose the correct ALB type, rules, and features.
Example Exam Scenario Questions
- Scenario: A web app must be available globally, route traffic only to healthy VMs, and maintain session for logged-in users.
Answer Mapping: Standard Load Balancer, health probes, client IP session persistence, public frontend. - Scenario: Internal database cluster should balance traffic within a VNet.
Answer Mapping: Internal Load Balancer (ILB), private frontend IP, backend pool = database VMs, Standard LB for production.
✅ Summary
Mapping requirements to Azure Load Balancer features is all about matching needs to features:
- Internal vs Public
- Basic vs Standard SKU
- Health probes for availability
- Load balancing rules for traffic
- Session persistence for sticky sessions
- Outbound connectivity for backend VMs
- Zone-redundancy for high availability
If you can systematically answer these 7–8 points, you can confidently map any requirement to the correct ALB feature in the exam.
