Cloud NAT for private instances in GCP - Commands & Configuration

Introduction

Private instances in a cloud network cannot access the internet directly. Cloud NAT lets these instances send requests outside without exposing them to incoming internet traffic.

When you have virtual machines without public IP addresses that need to download software updates.

When private instances must access external APIs or services securely without exposing their IPs.

When you want to keep your instances isolated from the internet but still allow outbound connections.

When you want to reduce security risks by avoiding public IPs on your instances.

When you need to manage internet access centrally for many private instances.

Config File - cloud_nat.yaml

cloud_nat.yaml

apiVersion: compute.cnrm.cloud.google.com/v1beta1
kind: ComputeRouter
metadata:
  name: example-router
  namespace: default
spec:
  networkRef:
    name: example-vpc
  region: us-central1
---
apiVersion: compute.cnrm.cloud.google.com/v1beta1
kind: ComputeRouterNat
metadata:
  name: example-nat
  namespace: default
spec:
  routerRef:
    name: example-router
  region: us-central1
  natIpAllocateOption: AUTO_ONLY
  sourceSubnetworkIpRangesToNat: ALL_SUBNETWORKS_ALL_IP_RANGES
  logConfig:
    enable: true
    filter: "ERRORS_ONLY"

This file creates a Cloud Router named example-router in the us-central1 region linked to the example-vpc network. Then it creates a Cloud NAT configuration example-nat attached to that router.

The NAT uses automatic IP allocation and applies to all subnetworks and IP ranges in the VPC. Logging is enabled to capture errors only.

Commands

This command creates the Cloud Router and Cloud NAT resources in your Google Cloud project using the configuration file.

Terminal

kubectl apply -f cloud_nat.yaml

Expected Output

computerrouter.compute.cnrm.cloud.google.com/example-router created

computerouternat.compute.cnrm.cloud.google.com/example-nat created

This command checks the details of the Cloud NAT configuration to confirm it is set up correctly.

Terminal

gcloud compute routers nats describe example-nat --router=example-router --region=us-central1

Expected Output

name: example-nat

region: us-central1

natIpAllocateOption: AUTO_ONLY

sourceSubnetworkIpRangesToNat: ALL_SUBNETWORKS_ALL_IP_RANGES

logConfig:

  enable: true

  filter: ERRORS_ONLY

→

--router - Specifies the router the NAT is attached to

→

--region - Specifies the region of the router and NAT

This command verifies that the private instance has no external IP but can still access the internet through Cloud NAT.

Terminal

gcloud compute instances describe private-instance-1 --zone=us-central1-a

Expected Output

name: private-instance-1

networkInterfaces:

- networkIP: 10.128.0.5

  accessConfigs: []

→

--zone - Specifies the zone of the instance

Key Concept

Cloud NAT allows private instances without public IPs to access the internet securely by translating their outbound traffic through a managed gateway.

Common Mistakes

Not creating a Cloud Router before setting up Cloud NAT

Cloud NAT requires a Cloud Router to function; without it, NAT cannot be configured.

Always create and configure a Cloud Router in the same region and network before creating Cloud NAT.

Assigning public IPs to private instances expecting NAT to be used

If instances have public IPs, they do not use Cloud NAT for outbound traffic, defeating the purpose of private instances.

Ensure instances have no external IPs to use Cloud NAT for outbound internet access.

Not specifying the correct subnetworks or IP ranges in NAT configuration

Cloud NAT will not apply to instances outside the specified subnetworks, causing connectivity failures.

Use ALL_SUBNETWORKS_ALL_IP_RANGES or specify subnetworks explicitly to cover all private instances.

Summary

Create a Cloud Router in your VPC network and region.

Configure Cloud NAT attached to the router to enable internet access for private instances.

Verify the NAT setup and confirm private instances have no public IP but can reach the internet.

Practice

1. What is the main purpose of Cloud NAT for private instances in Google Cloud?

easy

A. Create a VPN connection between private instances

B. Assign public IP addresses to all instances automatically

C. Allow private instances to access the internet without public IP addresses

D. Enable inbound internet traffic to private instances

Solution

1. Step 1: Understand Cloud NAT's role

   Cloud NAT allows private instances to send outbound traffic to the internet without needing public IPs.

2. Step 2: Eliminate incorrect options

   Assigning public IPs automatically, creating a VPN connection between private instances, and enabling inbound internet traffic to private instances describe different functions not provided by Cloud NAT.

3. Final Answer:

   Allow private instances to access the internet without public IP addresses -> Option C

4. Quick Check:

   Cloud NAT = outbound internet without public IP [OK]

Hint: Cloud NAT = outbound internet for private instances [OK]

Common Mistakes:

• Confusing Cloud NAT with assigning public IPs
• Thinking Cloud NAT allows inbound internet traffic
• Mixing Cloud NAT with VPN functionality

2. Which of the following is the correct way to configure Cloud NAT in Google Cloud Console?

easy

A. Create a firewall rule allowing inbound NAT traffic

B. Create a Cloud Router, then add a Cloud NAT configuration linked to it

C. Enable Cloud NAT on the VM instance network interface

D. Directly assign a public IP to each private instance

Solution

1. Step 1: Identify Cloud NAT setup steps

   Cloud NAT requires a Cloud Router to manage NAT configurations.

2. Step 2: Review options for correctness

   Create a Cloud Router, then add a Cloud NAT configuration linked to it correctly describes creating a Cloud Router and linking Cloud NAT. Assigning public IPs to private instances and enabling NAT on VM interfaces directly are incorrect because Cloud NAT does not work that way. Creating a firewall rule allowing inbound NAT traffic is wrong because NAT does not require inbound firewall rules.

3. Final Answer:

   Create a Cloud Router, then add a Cloud NAT configuration linked to it -> Option B

4. Quick Check:

   Cloud NAT setup = Cloud Router + NAT config [OK]

Hint: Cloud NAT always needs a Cloud Router first [OK]

Common Mistakes:

• Trying to assign public IPs to private instances
• Enabling NAT directly on VM interfaces
• Confusing firewall rules with NAT configuration

3. Given this snippet of a Cloud NAT configuration in Terraform, what will happen if private instances try to access the internet?

resource "google_compute_router" "router" {
  name    = "my-router"
  network = "default"
  region  = "us-central1"
}

resource "google_compute_router_nat" "nat" {
  name                               = "my-nat"
  router                             = google_compute_router.router.name
  region                             = "us-central1"
  nat_ip_allocate_option             = "AUTO_ONLY"
  source_subnetwork_ip_ranges_to_nat = "ALL_SUBNETWORKS_ALL_IP_RANGES"
}

medium

A. Private instances will access the internet using automatically allocated NAT IPs

B. Private instances will fail to access the internet due to missing public IPs

C. Only instances with public IPs will access the internet

D. The NAT configuration will block all outbound traffic

Solution

1. Step 1: Analyze Terraform NAT configuration

   The NAT uses AUTO_ONLY for IP allocation and applies to all subnetworks and IP ranges, allowing private instances to use NAT IPs automatically.

2. Step 2: Determine expected behavior

   Since NAT IPs are auto-allocated and all subnetworks are included, private instances will access the internet through NAT IPs.

3. Final Answer:

   Private instances will access the internet using automatically allocated NAT IPs -> Option A

4. Quick Check:

   Auto NAT IPs + all subnetworks = internet access [OK]

Hint: AUTO_ONLY means NAT IPs assigned automatically [OK]

Common Mistakes:

• Assuming private instances need public IPs
• Thinking NAT blocks outbound traffic
• Confusing source_subnetwork_ip_ranges_to_nat setting

4. You configured Cloud NAT but private instances still cannot access the internet. What is the most likely cause?

medium

A. The instances have public IPs assigned

B. Cloud NAT is configured with AUTO_ONLY IP allocation

C. Firewall rules allow outbound traffic

D. The Cloud Router is not in the same region as the instances

Solution

1. Step 1: Check Cloud NAT regional requirements

   Cloud NAT and Cloud Router must be in the same region as the instances to route traffic correctly.

2. Step 2: Evaluate other options

   The instances have public IPs assigned is not a problem; public IPs are optional. Firewall rules allow outbound traffic is good practice, not a cause of failure. Cloud NAT is configured with AUTO_ONLY IP allocation is a valid IP allocation method.

3. Final Answer:

   The Cloud Router is not in the same region as the instances -> Option D

4. Quick Check:

   Cloud Router region mismatch blocks NAT [OK]

Hint: Cloud Router and NAT must match instance region [OK]

Common Mistakes:

• Assuming public IPs are required for NAT
• Ignoring region mismatch issues
• Confusing firewall rules with NAT problems

5. You want to allow private instances in multiple subnetworks across different regions to access the internet using Cloud NAT. Which setup is best practice?

hard

A. Create a Cloud Router and Cloud NAT in each region, linked to subnetworks in that region

B. Create one Cloud Router and Cloud NAT in a single region for all subnetworks

C. Assign public IPs to all instances instead of using Cloud NAT

D. Use a single Cloud Router with multiple NAT configurations in one region

Solution

1. Step 1: Understand Cloud NAT regional scope

   Cloud NAT and Cloud Router are regional resources; they must be created in each region where subnetworks exist.

2. Step 2: Evaluate options for multi-region setup

   Create a Cloud Router and Cloud NAT in each region, linked to subnetworks in that region correctly creates routers and NATs per region. Create one Cloud Router and Cloud NAT in a single region for all subnetworks and using a single Cloud Router with multiple NAT configurations in one region incorrectly assume cross-region coverage. Assigning public IPs to all instances instead of using Cloud NAT avoids NAT but is less secure and not best practice.

3. Final Answer:

   Create a Cloud Router and Cloud NAT in each region, linked to subnetworks in that region -> Option A

4. Quick Check:

   Cloud NAT is regional, so multi-region needs multiple routers [OK]

Hint: Cloud NAT is regional; create per region needed [OK]

Common Mistakes:

• Trying to use one NAT for all regions
• Assigning public IPs instead of NAT
• Misunderstanding Cloud NAT regional limits