Support for getting SNAT Ports from Load Balancer/AKS (data "azurerm_lb_outbound_rule")

[ElvenSpellmaker]

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Description

Due to the low SNAT port defaults of 1024 (even when you have a few nodes) when using the default Load Balancer configuration in Kubernetes and ran into SNAT port exhaustion.
(Moving to NAT Gateway isn't an option at the present time but still.)

We've since done this in our K8s to up the amount of allocated ports, allowing us to have 10 nodes:

...
    load_balancer_profile {
      outbound_ports_allocated = "5816"
      idle_timeout_in_minutes  = "4"
    }
...

However there's no way for us to retrieve the number, which we'd love so we may alert on X% of SNAT ports used for example, as there's no data source for Outbound Rules.

It'd be nice to expose this from the outputs of azurerm_kubernetes_cluster as well seeing as we set this from this resource (but no way of retrieving it), but at least some way of getting them (i.e. data "azurerm_lb_outbound_rule) would be great.

New or Affected Resource(s)/Data Source(s)

azurerm_lb_outbound_rule (new data), azurerm_kubernetes_cluster (affected data)

Potential Terraform Configuration

No response

References

https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-outbound-connections

[aristosvo]

Hi @ElvenSpellmaker! Thanks for raising this.

Is there at this moment a way to get the number you are looking for? I mean, in your example you are setting a value, is this the same value expected as an output, like:

NODE_RG=$(az aks show --resource-group myResourceGroup --name myAKSCluster --query nodeResourceGroup -o tsv)
az network lb outbound-rule list --resource-group $NODE_RG --lb-name kubernetes -o table

An example how to solve this via az or Azure Portal might help get your issue resolved sooner. If this is not possible at the moment, I would advise to raise this at Microsoft side first.

[ElvenSpellmaker]

Hi @ElvenSpellmaker! Thanks for raising this.

Is there at this moment a way to get the number you are looking for? Via az or the portal maybe? An example might help get your issue resolved sooner.

If this is not the case, I would advise to raise this at Microsoft side first.

Hey, you can definitely see the number in the portal (from my screenshot above)
I'll check az when I can.

https://user-images.githubusercontent.com/2286713/201972120-5758db8f-7753-4f0a-a84c-6b83b0023cc9.png

[aristosvo]

So to understand what you're looking for, correct me if I'm wrong:

• You set a value for the AKS resource
• You want to get that same value as an output from a data source

Can you explain what the difference is between the two or why this helps?

[ElvenSpellmaker]

• Yeah we set a value in the AKS resource
• Under the hood it creates an lb with an outbound rule (https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/lb_outbound_rule)
• I'd like to get that value back either from a data resource from the lb rule, or from AKS (or both)

The use-case is so we can set an alert up on SNAT ports used as a % of the total allocated without having to hardcode it.

It's the same value, just it can't currently be retrieved in TF, but can be seen in the portal and set by both the AKS resource and by standalone outbound_rule resources.

See:

allocated_outbound_ports - (Optional) The number of outbound ports to be used for NAT. Defaults to 1024.

[ElvenSpellmaker]

Also for completeness to your original question, yes this can be obtained by az:

$ az network lb outbound-rule list -g MC-foo-bar-baz --lb-name kubernetes --subscription <sub>
[
  {
    "allocatedOutboundPorts": 5816,
...

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