Explanation/Reference: https://www.sovereignsolutionscorp.com/google-cloud-nat/

The most effective long-term solution to address IPv4 address exhaustion in GKE clusters, while still ensuring routability and unique ranges per cluster, is to transition to dual-stack IPv4/IPv6 clusters and leverage IPv6 for Pods and Services. This allows you to conserve IPv4 addresses for critical use cases while providing a vast address space with IPv6 for pods and services, significantly reducing the pressure on your private IPv4 ranges. Google Cloud GKE fully supports dual-stack networking.
Exact Extract:
"Dual-stack clusters enable you to assign both IPv4 and IPv6 addresses to Pods and Services. This approach helps conserve IPv4 address space by shifting a significant portion of the network communication to IPv6, particularly for internal cluster communication or communication with other IPv6-enabled services."
"When you enable dual-stack networking, GKE assigns an IPv6 address range to your Pods and can also assign IPv6 addresses to Services. This significantly expands the available addressing capacity within your cluster."Reference: Google Kubernetes Engine Documentation - Dual-stack networking

* Create Packet Mirroring Policies:
* You need to create three packet mirroring policies, one for each zone (us-west2-a, us-west2-b, and us-west2-c). This ensures that each zone's traffic is mirrored appropriately without unnecessary cross-zone traffic.
* Create Collector Instances:
* Set up one group of collector instances for the us-west2 region. Having a single group of collector instances for the entire region minimizes the number of instances required and simplifies the management while keeping egress costs low since the collectors are within the same region.
* Configuration of Policies:
* Each packet mirroring policy should be configured to match traffic for its specific zone. Use instance-tags to identify and match the relevant instances within each zone. This helps in correctly capturing the traffic from the appropriate sources.
* Filter for TCP Traffic:
* Create a filter for TCP traffic (ports 80 and 443). This step ensures that only the relevant web application traffic is mirrored, reducing the amount of data processed and improving efficiency.
* Cost Efficiency:
* By having packet mirroring policies specific to each zone and a regional collector group, you reduce inter-zonal network egress costs. The data remains within the same region, avoiding extra charges associated with cross-zone traffic.

For the Dedicated Interconnect to be the primary connection over the HA VPN, you should:
Enable global dynamic routing mode to allow the VPC to distribute routes dynamically across regions.
Set the BGP priority for the VLAN attachments associated with the Dedicated Interconnect to a lower base priority (e.g., 100) than the HA VPN's priority (e.g., 20000) to ensure it is preferred.
Setting up global dynamic routing with adjusted BGP priorities on both Interconnect and VPN will allow dynamic routing of traffic based on set preferences and path attributes, such as MED and priority levels. This setup ensures the Dedicated Interconnect, with a lower priority value, becomes the primary path for traffic, while the HA VPN, with a higher priority, serves as a backup.