Load Balancer Backend Memebrs Health Status

Mohamad Swead 0

Hello,

I have a standard Azure LB configured with two servers in the backend. TCP health prob is configured to monitor the backend servers over port 80 with an interval of 5 seconds.

When shutting down one of the VMs in the backend, the status of the stopped VM remains healthy for over than 5 minutes before being marked as unhealthy. Almost the same time is needed to re mark the VM as healthy after starting the VM.

Any idea why having this unexpected behavior ?

Thanks in advance.

GitaraniSharma-MSFT 49,261 Reputation points Microsoft Employee

2023-07-25T12:55:31.91+00:00

Hello @Mohamad Swead ,

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

I understand that you've a standard Azure Load Balancer configured with two servers in the backend, where TCP health probe is configured to monitor the backend servers over port 80 with an interval of 5 seconds but when you shut down one of the VMs in the backend, the status of the stopped VM remains healthy for over than 5 minutes before being marked as unhealthy.

May I know how you are validating the backend VM's health status?

Regards,

Gita
Mohamad Swead 0 Reputation points

2023-07-26T03:19:51.23+00:00

Hello @GitaraniSharma-MSFT

I'm validating the stopped backend VM health status by trying to connect into it from another VM within the same subnet. The VM is stopped and should not receive traffic, however, on the load balancer, i still can see it as healthy for almost 5 minutes as mentioned before.
GitaraniSharma-MSFT 49,261 Reputation points Microsoft Employee

2023-07-26T09:27:07.9366667+00:00

@Mohamad Swead , thank you for the update.

What I wanted to know is how are you validating the stopped backend VM's health status showing healthy on the load balancer?

Are you checking a particular metric in the load balancer? If yes, could you please share the same, so that I can test it in my lab and investigate further?

Regards,

Gita
GitaraniSharma-MSFT 49,261 Reputation points Microsoft Employee

2023-08-01T12:32:50.8066667+00:00

@Mohamad Swead , could you please provide an update on this post?

1 answer

msrini-MSFT 9,271 Reputation points Microsoft Employee

2023-07-28T03:39:05.9833333+00:00

Hi, I believe there are no data path issues when you turn off one for the backend VM. If that is the case, then load balancer is working as expected. It's the metric which shows unhealthy in a delay which I think creates confusion here. If you can repeat the same excercise again and bring back the VM up after 15 mins. Once the VM is back online, can you please take a screenshot of the probe metric and share it here? Ideally I should see the 15 mins probe down in the metrics.
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Load Balancer Backend Memebrs Health Status

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