Azure Load Balancer

  • Distributes incoming network traffic across multiple targets.
  • Allows you to route traffic based on source IP address and port to a destination IP address and port.


  • The load balancer supports TCP/UDP-based protocols.
  • Scales automatically as traffic increases.
  • The load-balancing decision is based on the following tuple connection:
    • Source IP address and port
    • Destination IP address and port
    • Protocol
  • NAT allows you to control the inbound and outbound network traffic.
    • Inbound rules –  traffic allowed to a specific virtual machine or instance in the backend pool.
    • Outbound rules – enable all resources to communicate to the Internet.
  • Control the flow of traffic inside your private virtual network using an internal load balancer.
  • You can use a public load balancer to allow outbound connections for your virtual machines.
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  • Azure Load Balancer supports IPv6.
  • Load balancer tiers: Basic and Standard


  • A group of VMs or instances in a VM scale set serving the incoming request is called backend pool.
  • Determine the health status of backend pool instances with health probes
    • Health probe down behavior – if the probes in a backend pool fail, it will stop receiving traffic until it starts passing health probes again.
  • Standard load balancer availability zones:
    • Zonal = single zone
    • Zone-redundant = multiple zones
  • Use Azure Monitor to check the metrics, alerts, and resource health of Azure Load Balancer.
  • High Availability (HA) ports enable load balancing on all ports of TCP and UDP protocols.
  • With multiple frontends, you can load balance services on multiple ports and multiple IP addresses.
  • SLA guarantees that two or more healthy VMS will always be available.


Basic Load Balancer

Standard Load Balancer

Backend pool size

Supports up to 300 instances.

Supports up to 1000 instances.

Backend pool endpoints

A single availability set for VMs or VM scale set.

A single virtual network for any VMs or VM scale sets.

Health probes



Health probe down behavior

TCP connections stay alive on an instance probe down. All TCP connections terminate when all probes are down.

TCP connections stay alive on an instance probe down and on all probes down.

Availability Zones

Not available

Zone-redundant and zonal frontends for inbound and outbound traffic.


Azure Monitor logs

Azure Monitor multi-dimensional metrics

HA Ports

Not available

Available for Internal Load Balancer

Secure by default

Open by default. Network security group optional.

Closed to inbound flows unless allowed by a network security group. Please note that internal traffic from the VNet to the internal load balancer is allowed.

Outbound Rules

Not available

Declarative outbound NAT configuration

TCP Reset on Idle

Not available

Available on any rule

Multiple frontends

Inbound only

Inbound and outbound

Management Operations

60-90+ seconds typical

Most operations < 30 seconds


Not available


  • Frontend IP configuration
    • Public load balancer = public IP address
    • Internal load balancer = private IP address
  • Backend pools
    • The resources in the backend pool come from a single virtual network.
    • You can associate the backend pool to a VM or VM scale set.
  • Load Balancing Rules
    • A load balancing rule distributes the incoming traffic to the resources in the backend pool.
    • The IP version you can select is between IPv4 and IPv6.
    • You can only assign a frontend IP address that has one public IP address.
    • Select between TCP and UDP protocols.
    • Health probes can determine which VMs in the backend pool can receive the load-balanced traffic.
    • Session persistence maintains the traffic from a client to the same virtual machine.
      • None – any virtual machine can handle successive requests from the same client.
      • Client IP – the same virtual machine will handle successive requests from the same client IP address.
      • Client IP and protocol – the same virtual machine will handle successive requests from the same client IP address and protocol combination.
    • Idle timeout keeps a TCP or HTTP connection open without depending on the clients to send keep-alive messages.
    • If the connection is idle, you can use a TCP reset.
    • Floating IP changes the IP address mapping to the frontend IP of the load balancer.


  • You are charged based on the number of outbound rules.
  • You are billed for the first five rules of load balancing.
  • You are not charged for the NAT rules.

Azure Load Balancer vs App Gateway vs Traffic Manager:

How to Create a Load Balancer

Want to learn more about Azure? Watch the official Microsoft Azure YouTube channel’s video series called Azure Tips and Tricks.


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