Azure Load Balancer Distribution Modes & Zones

Azure Distribution Modes

Azure Load balancer supports below distribution Modes for routing connections to instances in the backend pool. 

Hash Based

In this mode , Azure load balancer uses five tuple hash based distribution mode by default. 

• Source IP
• Source Port 
• Destination IP
• Destination Port 
• Protocol Type

The hash is used to route traffic to healthy backend instances within the backend pool. When a client starts a new session from the same source IP, the Source Port changes and traffic goes to different backend instances. 

To configure this feature , you must select session persistence to be None in Azure Portal. 

Session Persistence

It is also called session affinity , Source IP affinity , or client IP affinity. It uses two tuples ( Source IP and Destination IP )  or three tuples ( Source IP and Destination IP , protocol type) hash to route to backend instances. 

When using session Persistence , connections from the same client will always go to the same backend instance within the backend pool. 

Use-cases 

• It solves the incompatibility between Azure Load Balancer and Remote Desktop gateway ( RD gateway) 
• When media is uploaded , data uploads happen through UDP , but control planes are achieved via TCP. 

Load Balancer Availability Zones

Azure Load balancer supports Availability zones, Enterprise can use standard Load balancer to increase the availability throughout their environment by aligning resources with , and distribution across zones. 

An Azure load balancer can be in three mode: 

• Zone Redundant
• Zonal 
• Non-Zonal

Zone Redundant

In a region with Availability zones , a Standard load balancer can be zone-redundant and traffic will be served by a single IP address. 

Frontend IP is used to reach all backend pool members distributed across different AZ. If one or more AZ fails , then the data path still survives as long as one zone in the region remains healthy. 

Below figure describes the Zone Redundant Load balancer. 

Zonal 

In this Enterprise choose to have a frontend to a single zone , called Zonal. It means any inbound or outbound flow is served by a single zone in a region. Data path is unaffected by failures in zones other than where it was guaranteed. Enterprise can use zonal frontends to expose an IP address per Availability Zones.