Can't add vmss to azure load balancer backend pool

Anirudh Mounasamy 101 Reputation points
2023-02-20T04:43:52.4133333+00:00

Hi,

I'm facing an issue with azure load balancer that when I try to add a vmss into the backend pool it's not getting added.azueree2

I'm seeing that under resource name there is no instances but just now I have added a vmss into it.

I'm not sure about the message above

{Backend pool <BEpoolname> was added to Virtual machine scale set <VMSS_name> Upgrade all the instances of <VMSS_name> for this change to work}

Can anyone tell me what does this mean or what do I need to do?

Azure Load Balancer
Azure Load Balancer
An Azure service that delivers high availability and network performance to applications.
416 questions
Azure Virtual Machine Scale Sets
Azure Virtual Machine Scale Sets
Azure compute resources that are used to create and manage groups of heterogeneous load-balanced virtual machines.
360 questions
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Accepted answer
  1. vipullag-MSFT 25,606 Reputation points
    2023-02-20T05:55:08.1466667+00:00

    Hello Anirudh Mounasamy

    Welcome to Microsoft Q&A Platform, thanks for posting your query here.

    The message you see the Azure Portal indicates that the backend pool was successfully added to the Azure load balancer, but for the change to take effect, you need to upgrade all the instances of the virtual machine scale set (VMSS) that you added to the backend pool.

    When you add a VMSS to a backend pool, the load balancer needs to know the IP addresses of the instances in the VMSS to route traffic to them. However, these IP addresses are not available until the VMSS instances are created or updated. When you upgrade the VMSS, new instances are created or existing ones are updated with new IP addresses, which allows the load balancer to route traffic to them.

    Refer below articles, for configuring a Virtual Machine Scale Set with an existing Azure Load Balancer,

    Azure PowerShell: https://video2.skills-academy.com/en-us/azure/load-balancer/configure-vm-scale-set-powershell

    Azure CLI: https://video2.skills-academy.com/en-us/azure/load-balancer/configure-vm-scale-set-cli

    Azure Portal: https://video2.skills-academy.com/en-us/azure/load-balancer/configure-vm-scale-set-portal

    To upgrade the VMSS and add the instances to the backend pool from Azure Portal, you can follow these steps:

    1. Navigate to the Azure portal and select the VMSS that you want to add to the backend pool.
    2. Select "Update" from the top menu and then select "Upgrade".
    3. Choose the appropriate upgrade policy and configure any other settings as needed.
    4. Review and validate the upgrade, then click "OK" to initiate the upgrade.

    Once the upgrade is complete, the instances in the VMSS should have IP addresses that the load balancer can use to route traffic to them, and the backend pool should be fully functional.

    Hope this helps.

    If you need further help on this, tag me in a comment.

    If the suggested response helped you resolve your issue, please 'Accept as answer', so that it can help others in the community looking for help on similar topics.

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  1. Noble Kyeremateng 0 Reputation points
    2023-04-09T00:09:52.8266667+00:00

    When creating the VMSS, select "uniform" as the orchestration mode. This will enable you to update the instances when they are added to the LB backend pool. Choosing flexible mode does support an upgrade.

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