Azure Load Balancer gives cloud architects a reliable way to spread network requests evenly across VMs and services, cutting the risk of any single resource becoming a traffic hotspot. From dozens of projects, I have learned that a clear grasp of its costs and capabilities turns guesswork into planning and stops unexpected bills midway through production.
In this guide, I’ll walk you through the details of the service's core features, outline its four cost channels, and share best practices that will point you to the setup that meets your workload.
What is Azure Load Balancer?
Azure Load Balancer is a managed Layer-4 networking appliance that sits between incoming connections and the backend resource pool, forwarding packets only to healthy nodes as confirmed by user-defined health probes. By acting as a front-door proxy, it shields customers from the specifics of instance availability and steers traffic in milliseconds, creating a seamless experience even during partial outages.
Balanced traffic lightens the load on individual servers, reducing response times and preventing cascading failures that occur when one node is flooded with requests. When deployed correctly, the Load Balancer lifts overall application uptime, smoothes peak-period performance, and fortifies the end-user experience against the unexpected.
Key Benefits:
Increased Availability and Resilience: Azure Load Balancer continually monitors the health of individual servers, automatically rerouting incoming requests away from any instance that is not fully operational. This feature proves critical during scheduled maintenance, unexpected hardware failures, or sudden traffic storms that could otherwise overtax a single node.
Scalability: As new virtual machines are provisioned, the service seamlessly incorporates them into the traffic distribution algorithm, spreading requests evenly across the expanded pool. This elastic behaviour helps ensure that response times remain consistent, even as user volumes fluctuate throughout the day.
Built-in Security: At the network layer, Azure Load Balancer works in tandem with Network Security Groups and can be augmented with Azure DDoS Protection, considerably lowering the attack surface exposed to the Internet. By filtering potentially harmful packets before they reach backend servers, these combined controls shield workloads from volumetric and protocol-based threats.
Types of Azure Load Balancers
Azure offers three distinct load balancer SKUs, each tailored to different scenarios and performance needs.
Standard Load Balancer
The Standard SKU is the most feature-rich option; it scales to 1,000 backend instances and includes:
Zone-redundant deployment across multiple availability zones.
Support for both IPv4 and IPv6 protocols.
High availability ports for complex multi-tier apps.
Azure Monitor integration for granular performance metrics.
Outbound rules that define and control egress patterns.
This SKU works well for production workloads that demand fault tolerance, high availability, detailed monitoring, and advanced networking features.
Basic Load Balancer
The Basic SKU delivers fundamental distribution for smaller deployments with lighter needs:
Support for up to 300 backend instances.
Basic health probing functionality.
Deployment is restricted to a single availability zone.
No advanced monitoring or diagnostic features.
Important Note: Microsoft plans to retire Basic Load Balancer on September 30, 2025, so users should migrate to Standard before that deadline.
Gateway Load Balancer
The Gateway Load Balancer SKU addresses specific use cases centred on network virtual appliances and service chaining:
It allows third-party network appliances to be added without modifying user traffic.
It orchestrates service chaining in sophisticated network designs that require multiple inspection points.
Provides high availability for network virtual appliances.
Simplifies deployment compared to traditional dual load balancer setups.
For public traffic, the Public Load Balancer provides a single point of exposure, while the Internal Load Balancer routes inter-service traffic securely inside the Azure region.
How Azure Load Balancer Works
Azure Load Balancer relies on several tightly integrated components that together shape the flow of incoming network traffic.
Frontend IP Configuration
A Frontend IP configuration specifies the entry point through which customers reach the service. For a public load balancer, that means a publicly reachable IP address that sits at the edge of the Azure network; for an internal load balancer, it means a private IP assigned to a subnet, allowing communication only within the designated virtual network or through a connected on-premises device.
Backend Pools and Health Probes
Backend pools group the VMs or VM scale sets that are eligible to handle the traffic. To keep that pool reliable, health probes run periodic checks against designated ports or HTTP endpoints, signalling to the system whether each instance is ready to accept requests and is functioning properly.
When a probe marks an instance as unhealthy, the load balancer automatically removes it from the active pool until the readiness test passes again, giving users a seamless experience even during brief outages.
Load Balancing Rules and Session Persistence
Load-balancing rules specify the method used to spread incoming requests across available backend instances. The Azure Load Balancer offers several distribution methods:
5-tuple hash (default): Distributes traffic based on source IP, source port, destination IP, destination port, and protocol
2-tuple hash: Uses only source IP and destination IP to guide the routing traffic decision.
3-tuple hash: Uses source IP, destination IP, and protocol for distribution decisions
Session persistence, often called session affinity, instructs the load balancer to forward subsequent requests from an individual client to the same backend node. This behaviour is crucial for applications that store temporary data on the server between successive client interactions.
Key Features Explained
Health Probes for Monitoring
Azure Load Balancer uses three kinds of health probes to check the backend instance status:
HTTP probes send requests to defined URLs and expect expected status codes in return.
HTTPS probes do the same check, but the traffic runs over SSL-TLS to verify encrypted paths.
TCP probes attempt to open a raw socket on a given port, confirming the port is open and listening.
When these probes are set up correctly, the Load Balancer quickly learns which instances are healthy and avoids sending new requests to those that have failed.
Zone Redundancy and High Availability
Zone redundancy spreads the Load Balancer's control plane and data plane resources across each availability zone in a given region. Because of this layered architecture, even full-power failures affecting one zone do not interrupt traffic, allowing the application to fail over gracefully to neighbouring zones.
IPv6 Support and Protocol Flexibility
Standard Load Balancer accepts both IPv4 and IPv6, letting companies merge legacy and modern address schemes without separate front-ends. The service forwards both TCP and UDP packets, covering nearly every common enterprise protocol in use today.
Integration with Azure Monitor
Azure Monitor ties directly to the Load Balancer, giving operators a single pane to watch performance:
Real-time metrics for connection counts, data throughput, and health probe status.
Diagnostic logs for troubleshooting and audit purposes.
Custom alerts based on performance thresholds.
Integration with Azure Log Analytics for advanced analysis.
Azure Load Balancer Pricing Explained
Azure Load Balancer pricing varies by SKU and includes several components that companies should understand for accurate cost planning.
Standard Load Balancer Pricing
Standard Load Balancer adopts a pay-as-you-go model that separates hourly and data-processing charges:
Hourly Charges
First, 5 load balancing rules: $0.025 per hour
Additional rules: $0.01 per rule per hour
Inbound NAT rules: Free
Data Processing Charges
Regional tier: $0.005 per GB of data processed
Global tier: No additional charge for data processed
The data-processing charge applies to every byte that passes through the Load Balancer; administrators must factor in traffic sent to Azure PaaS endpoints and packets exchanged between virtual machines in the same VNet.
Gateway Load Balancer Pricing
Gateway Load Balancer has three charge components:
Gateway hour: $0.013 per hour
Chain hour: $0.01 per hour (for service chaining configurations)
Data processed: $0.004 per GB
Cost Optimization Strategies
Eliminate Unnecessary Rules: After the first five rules, each additional entry generates an extra hourly cost. Schedule periodic audits of your rule set, so you keep only those that drive traffic and discard the rest.
Keep an Eye on Data Transfer Costs: Data processing charges climb quickly for sites with heavy visitor volumes. Plug-ins such as Azure Front Door or Azure CDN spread content across regional nodes, relieving the load balancer and trimming outbound costs.
Use Azure Reserved Instances: When traffic patterns are stable, Reserved Instances cut the VM bill for the load-balancer cluster substantially. Committing to these longer-term plans lets you safeguard performance while securing predictable savings.
Azure Load Balancer vs. Application Gateway
Understanding how Azure Load Balancer and Application Gateway differ helps teams select the best service for their workloads.
When to Choose Azure Load Balancer
Azure Load Balancer shines in situations that demand:
Layer 4 load balancing for both TCP and UDP traffic.
High performance with low latency across all connections.
Simple configuration and management.
Cost-effective load balancing for straightforward applications.
When to Choose Application Gateway
Application Gateway stands out for HTTP and HTTPS traffic because it offers:
Layer 7 load balancing with URL-based routing
SSL offload and automated certificate renewal.
Integrated Web Application Firewall with active threat protection.
Cookie-based session persistence for stateful applications.
Custom error pages and flexible redirection rules.
Note: Application Gateway carries a higher cost point than Azure Load Balancer, but its advanced features suit complex web environments.
Best Practices for Azure Load Balancer
Distribution Modes and Session Affinity
Select a distribution mode based on how your app behaves. The default 5-tuple hash spreads traffic evenly for most cases, but 2-tuple or 3-tuple hashes help when you need stronger session persistence.
Remember that forcing session affinity can leave some instances idle, especially if most requests come from a single client IP or narrow address range.
Security with Network Security Groups
Every deployment should include a well-designed set of Network Security Groups to manage how data enters and leaves the load balancer and its linked services. Think of an NSG as a set of adjustable doors; each rule opens or closes a pathway based on the port protocols and source addresses you specify.
Key security considerations include:
Allow only the ports and protocols absolutely needed by the application
Allowing health probe traffic from IP address 168.63.129.16
Follow the principle of least privilege access for all rules
Check and revise the rule set regularly to adapt to changing needs.
Monitoring and Diagnostics
Pro-active monitoring lets you spot slowdowns or failures before users notice:
Set up Azure Monitor alerts tied to key measures such as health probe success rates and live connection counts.
Turn on diagnostic logs so you can trace problems down to the packet level.
Use Azure Network Watcher to see a real-time map of traffic flow and to run basic connectivity tests.
Schedule performance drills to confirm that the load balancer handles expected bursts.
Scaling and Redundancy Strategies
Design your load balancer configuration with redundancy in mind:
Spread backend instances across at least two Availability Zones within the same region.
Keep a minimum of two healthy members in each backend pool, ready to take traffic.
For mission-critical services, think about cross-region load balancing as an extra line of defence.
Plan for automatic scaling based on traffic patterns and performance metrics.
How to Get Started with Azure Load Balancer
Use the Azure portal to create a new Load Balancer resource.
Configure frontend IP, backend pool, health probes, and load balancing rules.
Test your setup and monitor traffic using Azure Monitor.
Use the cost calculator to estimate ongoing expenses.
Choosing the Right Plan
Startups and small-to-medium-sized companies typically benefit from a Standard Load Balancer, assuming moderate traffic and regional deployment.
Larger enterprises should adopt a Zone Redundant Standard Load Balancer coupled with granular telemetry, which elevates both throughput and resilience.
Companies reliant on managed security or analytics appliances may find a Gateway Load Balancer preferable, as it orchestrates inspection while preserving session integrity.
For complex environments, tailored consultative engagements or fully managed packages can fine-tune routing policies, scale elastically, and routinely test failover scenarios.
Conclusion
Understanding Azure Load Balancer portfolio-and aligning it with company workloads-is foundational to dependable cloud architecture. By candidly charting traffic patterns, institutionalizing redundancy, and enlisting expert input at design and review milestones, firms can maintain a flexible, cost-efficient service front. Regular performance audits, security drills, and cloud-native telemetry then empower teams to mitigate risks, capitalise on regional latency gains, and underpin sustainable user growth.
Join Pump for Free
If you are an early-stage startup that wants to save on cloud costs, use this opportunity. If you are a start-up business owner who wants to cut down the cost of using the cloud, then this is your chance. Pump helps you save up to 60% in cloud costs, and the best thing about it is that it is absolutely free!
Pump provides personalized solutions that allow you to effectively manage and optimize your Azure, GCP and AWS spending. Take complete control over your cloud expenses and ensure that you get the most from what you have invested. Who would pay more when we can save better?
Are you ready to take control of your cloud expenses?
