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I'm running a small kubernetes cluster on GKE, and am providing a VPN connection (CloudVPN) into this VPC. I would like to restrict traffic entering the VPC via the VPN to only accessing an internal load balancer (ILB) I have setup for this purpose (allowing access to a service running within GKE). Unfortunately I'm struggling to work out the best way to restrict traffic for this particular use-case. It doesn't appear that I can set an ingress rule for traffic to the ILB, as GCP firewall ingress rules use tags to specify targets, which I can't set on the ILB.

Any suggestions for ways to implement this functionality would be appreciated. Not set on using GCP firewall rules - but it seemed like this would be the obvious way to implement this. I'm currently using another instance as a 'proxy' of sorts (which I can firewall as I can set instance tags) - but having another instance running as well as the ILB seems like overkill. My next branch of investigation will be to see whether I can setup the CloudVPN in a separate VPC and then use peering and routes to implement something along this path - although I suspect there may be issues here, and would prefer a mechanism that acts on ip:port rather than just ip.

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As you correctly stated there is not a way to limit incoming traffic on a Internal Load Balancer. Cloud Armor sound a good option, but as it mentioned here is not yet available for the Internal LB 1.

Although it looks an overkill, having an instance in front of the Load Balancer, may be the fastest and easier solution.

Another alternative similar to what you are proposing but much simpler is:

If you can recreate the VPN tunnel and if the only traffic you want to pass through it is the one going on the LB, you can limit the traffic selectors / BGP advertisements (Depending on the VPN type) to a subnet specifically designed for the Internal Load Balancer.

  1. Create a /29 subnet
  2. Create a Front End using an IP from that subnet.
  3. Configure the VPN to allow traffic from that subnet only.

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