Introduction
Load balancing is a critical aspect of modern network management, ensuring the efficient distribution of incoming traffic across multiple servers or resources. In Azure, load balancers play a key role in maintaining the performance, reliability, and availability of applications.
What is Load Balancing?
Load balancing refers to the method of distributing incoming network traffic across a group of backend servers or resources. This process helps in preventing any single server from becoming overloaded, thereby improving the overall performance and reliability of applications. In Azure, load balancers operate at the transport layer (Layer 4) of the OSI model, making decisions based on information available in the transport layer headers, such as TCP or UDP port numbers and IP addresses.
Types of Load Balancers
Azure provides two main types of load balancers, each designed for different use cases:
Public Load Balancer:
Purpose: Used to load balance internet traffic to Azure virtual machines (VMs).
Functionality: Provides outbound connections for VMs inside a virtual network by translating their private IP addresses to public IP addresses.
Use Case: Ideal for applications that need to serve clients over the Internet.
Internal (Private) Load Balancer:
Purpose: Used to load balance traffic within a virtual network.
Functionality: Routes traffic to backend pool members via private IP addresses, keeping the traffic internal to the network.
Use Case: Suitable for applications that do not require exposure to the internet and need to manage traffic within a virtual network.
Load Balancer Tiers
Azure load balancers are available in two tiers:
Regional:
Balances traffic within a single region.
Global:
Balances traffic across multiple regions, providing a higher level of redundancy and availability.
Load Balancer SKUs
Azure offers different SKUs for load balancers to cater to various performance and redundancy requirements:
Basic:
Features: Designed for small-scale applications with limited functionality and redundancy.
Backend Type: NIC-based.
Protocols: Supports TCP and UDP.
Expiring soon(According to azure)
Standard:
Features: Equipped for high-performance applications requiring ultra-low latency.
Backend Type: IP-based and NIC-based.
Protocols: Supports TCP and UDP.
Gateway:
- Features: Designed for non-Microsoft network virtual appliances.
Routing Preferences
Azure load balancers offer two routing preferences:
Microsoft Network:
- Routes traffic via the Microsoft global network, providing lower latency and higher reliability.
Internet:
- Routes traffic through the internet service provider network.
Key Concepts in Load Balancing
Frontend IP Configuration: The IP address of the load balancer, serving as the point of contact for clients. This can be a public or private IP address.
Backend Pool: A group of resources (e.g., VMs) that receive traffic from the load balancer.
Health Probe: A feature that detects the health status of application instances by sending periodic requests to check their availability and responsiveness.
Load Balancing Rule: Defines how incoming traffic is distributed to backend pool members, associating a frontend IP, backend pool, and health probe.
High Availability Ports: A load balancer rule configured with 'protocol - all and port - 0', enabling a single rule to load-balance all TCP and UDP flows arriving on all ports.
Inbound NAT Rule: Forwards incoming traffic to a specific VM in the backend pool.
Outbound Rules: It sets up Network Address Translation (NAT) for all VMs in the backend pool, allowing them to communicate outwardly while hiding their internal IP addresses.
Azure Health Probe
An Azure Load Balancer health probe is essential for maintaining the health and availability of your application instances. It sends periodic requests to instances to check if they are available and responds to requests, ensuring that only healthy instances receive traffic.
Conclusion
Understanding Azure load balancers and their configurations is crucial for designing resilient and high-performance applications. You can ensure efficient traffic distribution, enhanced security, and optimal application performance by leveraging the appropriate load balancer type, SKU, and routing preferences.
For further details on configuring Azure load balancers and best practices, refer to the Azure Load Balancer documentation.