About multi-network network policies

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This page explains how to control the network traffic flow between Pods and Services using firewall rules at the Pod level.

Network policies for applications help you define communication traffic rules between Pods. It controls how Pods communicate with each other within their applications and with external endpoints. You can enable network policy on Pod-networks in Google Kubernetes Engine (GKE) Enterprise edition clusters that have multi-network enabled. You can enforce network policies on additional Pod interfaces that correspond to user-specified Pod-networks.

Why use multi-network network policies

You might want to use multi-network network policies in the following scenarios:

• Enhanced network security: You want to isolate and protect sensitive workloads or data by defining network policies for specific Pod-networks. Multi-networking network policies limit exposure and reduce the attack surface.

• Fine-grained traffic control: You want to achieve precise control over traffic flow between Pods and Services on different Pod-networks, allowing for complex network topologies and security requirements.

• Multi-tenant environments: You want to create isolated networks for different tenants or applications, ensuring they can't interfere with each other's communication, while maintaining control over network access within each Pod-network.

• Optimize resource utilization: You want to implement network policies on specific Pod-networks to efficiently allocate resources and prioritize traffic based on application requirements, improving performance and reliability.

• Security for Containerized Network Functions (CNFs): You want to segregate management traffic from dataplane traffic within the same Pod, preventing potential security breaches and unauthorized access.

How multi-network network policies work with Pod-networks

The following diagram illustrates how network policies, applied to specific Pod-networks using annotations, control traffic flow between Pods within a GKE cluster.

The preceding diagram shows multiple worker nodes running Pods (containerized applications) and how they communicate within the same node or across different nodes using the network infrastructure. It also illustrates the use of network policies to control traffic flow and the segmentation of the network using VPCs and subnets for enhanced security and organization.

1. Isolates traffic with targeted Network Policies: The network policies only affect traffic on the "blue" Pod-network because of the annotation networking.gke.io/network: blue-Pod-network . Traffic on the default Pod-network remains unrestricted.
2. Enforces one-way traffic with Pod-network policies: In the preceding diagram, network policies allow Pod1 to send traffic to Pod2 on the "blue" Pod-network. Pod2 can't send traffic back to Pod1 on the same network. The network policy for Pods labeled 'test-app-2' functions as a one-way channel. It specifically allows outgoing traffic only towards Pods labeled 'test-app-3', preventing communication with other Pods like 'test-app-1'.
3. Allows outgoing traffic by default: If no egress policy is defined for a Pod (Pod1 in this example), all outgoing traffic is allowed by default on the "blue" network interface.
4. Ensures existing features compatibility: All standard GKE network policy options like label selectors and IP address blocks work with multi-network network policies.
5. Controls network policy scope with annotations:
   1. If you create a network policy without annotation, GKE applies multi-network network policies to all network interfaces on the Pods in the selected namespace, regardless of which Pod-networks they are connected to.
   2. If you include the annotation and specify the name of a valid Pod-network (for example, networking.gke.io/network: blue-Pod-network ), GKE applies the policy to Pods connected to that specific Pod-network.
   3. If the annotation references the Pod-network that doesn't actually exist in your cluster, GKE doesn't apply the network policy to any Pods at all. This is because no Pods are connected to the specified non-existent network.
6. Maintains cross-network communication for Pods with multiple network interfaces: If you apply a network policy to restrict traffic on a specific Pod-network within a Pod, it won't affect the traffic on other Pod-networks connected to the same Pod.

Benefits

Following are the benefits in using multi-network network policies:

• Improved Security: You can mitigate risks associated with unauthorized access and lateral movement within the GKE cluster by applying network policies at a granular level.

• Flexibility and Customization: You can tailor network policies to meet your specific security and traffic management needs for different Pod-networks by accommodating diverse workloads and applications.

• Simplified Network Management: You can avoid creating excessive Pod-networks and have fine-grained control over communication by using network policies, simplifying network management, and reducing complexity.

• Cost Optimization: By avoiding the need to create numerous Pod-networks, you can optimize resource utilization and reduce costs associated with network infrastructure.

• Enhanced Protection for CNFs: You can ensure the security and integrity of CNF deployments by isolating management and dataplane traffic, and by applying specific network policies to each deployment.

What's next

Control traffic flow between Pods and Services at Pod level