Understanding Usage of Additional Egress IP in Google Cloud NAT Setup for GKE Private Cluster

[Rohan9]

I've recently added a second egress IP to my Google Cloud NAT setup for a GKE private cluster. Previously, I had one egress IP that was whitelisted and working correctly. After encountering errors due to increased workload, I added the new egress IP.

Now, both the old whitelisted IP and the new egress IP are functioning. However, when I run curl http://ipecho.net/plain from within any pod, it consistently returns the new egress IP.

How can I determine the purpose and usage of the new egress IP? Is there a way to verify which outbound traffic is routed through it?

Additionally, since my old whitelisted IP was working, I'm curious about why it's not working now whether it serves a specific function such as failover or load balancing.

Are there specific monitoring tools, logging mechanisms, or network analysis techniques I can use to gain insights into the traffic patterns and utilization of each egress IP within my Cloud NAT setup?

Any advice or insights into managing multiple egress IPs in the context of a GKE private cluster would be greatly appreciated. Thank you!

[Marvin_Lucero]

Hi @Rohan9 ,

Cloud NAT is used to provide outbound internet access to the nodes in the cluster. When you have multiple egress IPs, the behavior of the outbound traffic depends on various factors such as load balancing, failover, and routing policies.

In your case, when you added a second egress IP, it's possible that the traffic is being distributed between the two IPs. This could be due to LB's mechanism or due to the routing policies configured in your environment.

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@Rohan9 wrote:

How can I determine the purpose and usage of the new egress IP? Is there a way to verify which outbound traffic is routed through it?

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To determine the purpose and usage of the new egress IP:

1. Check the Cloud NAT configuration: You can use the gcloud command to inspect the configuration of your Cloud NAT. This will provide you with information about the egress IPs and their associated routing rules.

2. Analyze the traffic patterns: You can use tools like Cloud Logging and Cloud Monitoring to analyze the traffic patterns and identify which IPs are being used for outbound traffic.

3. Use packet capture tools: You can use tools like tcpdump or Wireshark to capture the packets leaving your GKE nodes and analyze the source IPs to determine their usage.

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@Rohan9 wrote:

Additionally, since my old whitelisted IP was working, I'm curious about why it's not working now whether it serves a specific function such as failover or load balancing.

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Regarding the old whitelisted IP, the routing policies might have changed: If the routing policies have been updated to prefer the new egress IP, the old IP might not be used anymore. Or on the other hand, the load balancing mechanism might have changed: If the load balancing mechanism has been updated to distribute the traffic between the two IPs, the old IP might not be used anymore.

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@Rohan9 wrote:

Any advice or insights into managing multiple egress IPs in the context of a GKE private cluster would be greatly appreciated. Thank you!

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To manage multiple egress IPs in the context of a GKE private cluster, you can consider the following strategies:

- You can use a load balancer to distribute the traffic between the two egress IPs. 
- You can use routing policies to control the distribution of the outbound traffic between the two IPs. This will allow you to optimize the traffic flow and prevent any single IP from becoming a bottleneck.

[Rohan9]

Hey @Marvin_Lucero,
Thanks for providing such a great explanation,

Regarding the old whitelisted IP, the routing policies might have changed: If the routing policies have been updated to prefer the new egress IP, the old IP might not be used anymore. Or on the other hand, the load balancing mechanism might have changed: If the load balancing mechanism has been updated to distribute the traffic between the two IPs, the old IP might not be used anymore.

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I haven't changes any routing polices it just what I I look up cloud nat page there is warning message that cloud nat need extra ip, so I just added extra IP that's it.

To handle this type of cases like multiple egress ip,
 Do we need to enabled something from GCP end to make load balancing or failover or it is part of other end, where they whitelist these IPs.