feat: support multiple external VPN peering gateways

[doniz]

Hello,

we would like to add this feature because we see that we could have many VPN peering gateways on selected tunnels in the GCP console without any issue, but this Terraform module does not support that.

In our case, we have an HA VPN that is connected to 2 on-premise DCs and instead of creating a new VPN instance, we may create a new tunnel that is linked to the specific peering gateway.

First, I thought to redo the variable of peer_external_gateway to set list(object..., but I realized it became very complicated from Terraform's point of view. So I added an optional element peer_external_gateway_self_link in the tunnels list object, so we could pass a custom resource self_link and set var.peer_external_gateway to null to prevent creating resource inside of the module.

Feedback is welcome.
Thank you, Donatas

[doniz]

@imrannayer can I get approval?

[imrannayer]

@doniz thanks for the PR. Can you also add an example in examples folder. Follow same pattern as vpn_ha but change it for gcp to on-prem with multiple external vpn gateways.
You can put the example you added in README file. Just make sure you test it.

[imrannayer]

/gcbrun

[doniz]

@doniz thanks for the PR. Can you also add an example in examples folder. Follow same pattern as vpn_ha but change it for gcp to on-prem with multiple external vpn gateways. You can put the example you added in README file. Just make sure you test it.

Ok, will do today.

[doniz]

Hi @imrannayer, I added an example and I wonder about creating in GCP 2 additional VPNs to reproduce 2 On-Premise DCs, but this needs a lot more time investment by creating external IPs. I think it's doable, but it becomes the same as examples/vpn_ha (GCP to GCP) just through the global external VPN GW IP.

Let me know if that's good enough.

[imrannayer]

/gcbrun