Front Door Load balancing

Question

Hello everyone,

I am looking for detailed information on how Azure Front Door load balances between origins. I have found some helpful information at https://learn.microsoft.com/en-us/azure/frontdoor/routing-methods, but I still have some questions.

Assuming there are two origins available (A+B), and both have a priority of 1, latency sensitivity of 0, and a weight of 1000:

1. How will traffic be distributed?
2. If origin A becomes unhealthy, will B take over?

I would appreciate any insights the community can offer. Thank you.

Maybe you @GitaraniSharma-MSFT take on this?

Answer 1

@Nibbler ,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.

I understand that you would like to understand how AFD Traffic routing methods work.

We should follow the Overall decision flow chart

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1.How will traffic be distributed?

1. Available origins : A and B are available, so both A and B are selected
2. Priority : A and B have same priority of 1, so both A and B are selected
3. Latency signal (based on health probe) :
   1. Let us assume Latency sensitivity of 0 (0 is highly unlikely, but we shall go with it for this example) and origin group's latency sensitivity is set to 30 ms.
   2. Since 0ms is less than 30ms, both A and B are selected.
4. Weights: A and B both have a weight of 1000.
   1. This means, the total is 2000 (A+B)
   2. And then traffic distributed to A is 1000/2000 (A/Total) , which is 1/2
   3. And traffic distributed to B is 1000/2000 (B/Total) , which is 1/2

i.e., Traffic is distributed equally across A and B

2.If A becomes unhealthy,

1. Available origins : Since A is unhealthy, only B is selected
2. Since there is only one Origin now, no need for further validation.

i.e., 100% Traffic is routed to B

Kindly let us know if this helps or you need further assistance on this issue.

Thanks,

Kapil

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Answer 2

Azure Front Door supports four different traffic routing methods to determine how your HTTP/HTTPS traffic is distributed between different origins: Latency, Priority, Weighted, and Session Affinity. Assuming there are two origins available (A+B), and both have a priority of 1, latency sensitivity of 0, and a weight of 1000, traffic will be distributed evenly between the two origins. If origin A becomes unhealthy, Azure Front Door will automatically route traffic to origin B.

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References:

• Traffic routing methods to origin