My Azure Load Balancer NAT Rule Won’t Work (Why & Solution)

I’ve had a bug in Azure bite me in the a$$ every time I’ve run an Azure training course. I thought I’d share it here. The course that I’ve been running recently focuses on VM solutions in a CSP subscription – so it’s all ARM, and the problem might be constrained to CSP subscriptions.

When I create a NAT rule via the portal, most of the time, the NAT rule fails to work. For example, I create a VM, enable an NSG to allow RDP inbound, and create a load balancer NAT rule to enable RDP inbound (TCP 50001 –> 3389 for a VM) It appears like there’s a timing issue behind the portal, because eventually the NAT rule starts to work.

There’s actually a variety of issues with load balancer administration in the Azure Portal:

  • The second step in creating a NAT rule is when the target NIC is updated; this fails a high percentage of the time (note the target being set to “–“ in the rule summary).
  • Creating/updating a backend pool can fail, with some/none of the virtual machines being added to the pool.

These problems are restricted to the Azure Portal. I have no such issues when configuring these settings using PowerShell or deploying a new resource group using a JSON template. That’s great, but not perfect – a lot of general administration is done in the portal, and the GUI is how people learn.

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2 Comments on My Azure Load Balancer NAT Rule Won’t Work (Why & Solution)

  1. Funny you mention that cause I was having the very same problem and thought I was going mad

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