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To enforce zero network egress for Kubernetes pods, apply an egress-isolating default-deny NetworkPolicy, confirm that your network plugin enforces it, and test both allowed and blocked connections from representative workloads. Automate checks of the policy configuration and live traffic. These tests can show that specified workloads could not make specified outbound connections in a defined environment; network controls alone do not establish where data is stored or processed, or which legal regime governs it.
Define what “zero egress” covers
Here, “zero egress” means that in-scope Kubernetes pods cannot initiate outbound network connections unless an explicit exception allows them. It does not automatically cover node traffic, every host-networked pod, or systems outside the pod network. Nor does a blocked connection prove that data is stored in a particular place or subject to a particular law. Treat egress enforcement and data-sovereignty evidence as separate parts of the assessment.
Before writing a policy, record the boundary your tests are meant to cover:
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- Any excluded workloads, including pods using
hostNetwork, and how those paths are controlled or tested separately. - Which outbound destinations, ports, and protocols are genuinely required, and which exceptions are approved.
- Whether IPv4 and IPv6 are both in scope, and how DNS resolution is intended to work.
This matters because a namespace policy does not, by itself, demonstrate control of node or host-network traffic. Kubernetes documentation also describes limits such as no service-name targeting and no built-in network-event logging.
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Start with an egress default-deny policy
Kubernetes pods are non-isolated for egress by default: outbound connections are allowed unless an applicable egress policy isolates the pod. A namespace-level policy can select every pod and declare Egress without adding any egress rules:
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: default-deny-egress
namespace: YOUR_NAMESPACE
spec:
podSelector: {}
policyTypes:
- EgressReplace YOUR_NAMESPACE with the actual namespace name. This policy permits no egress under its own rules, including DNS. Add only narrowly scoped exceptions that are required and approved.
NetworkPolicies are namespace-scoped and additive for allowed traffic: for a selected pod, the permitted egress is the union of the egress rules in all applicable policies. A second policy that permits traffic therefore adds an allowance; it does not override the deny policy. Review the complete set of applicable policies, not just the default-deny object.
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Automate configuration checks and traffic probes
A useful test suite checks both what is configured and what a workload can do. Configuration checks catch missing or overly broad policy; runtime probes reveal whether the deployed enforcement path behaves as expected.
- Inventory the boundary. Enumerate in-scope namespaces, pod selectors, exceptions, and workloads outside the normal pod network. Include host-networked workloads as a separate case rather than assuming namespace coverage includes them.
- Assert the policy configuration. Check that each in-scope namespace has an egress-isolating default-deny policy. Inspect every additional applicable egress policy and compare its workload selector, destination, port, and protocol with the approved exceptions. Fail the test when an unapproved allowance appears.
- Check the enforcement precondition. Verify that the cluster’s network plugin supports and enforces NetworkPolicy. Record the plugin and relevant configuration alongside the test results.
- Probe from representative workloads. Attempt connections to approved destinations and confirm they work; attempt connections to disallowed destinations and confirm they fail. Test the workloads and policy scopes that matter rather than relying on a probe from an unrelated pod.
- Cover address families and name-based rules. Where IPv6 is in scope, test it as well as IPv4. For domain-based controls, test an approved name, an unlisted name, DNS resolution, and direct-IP attempts to the resolved or other external destinations.
- Retest changes and existing flows. After policy changes, distinguish new connection attempts from connections established earlier. Some provider-specific enforcement can leave established connections active until connection tracking closes them.
- Keep evidence with its limits. Store the policy state, probe outcomes, environment, and execution time. State which paths were not tested. If audit records are required, collect telemetry from the enforcement layer; Kubernetes NetworkPolicy does not provide built-in network-event logging.
Google Cloud Policy Controller’s K8sRequireDefaultDenyEgressPolicy constraint template can require a default-deny egress NetworkPolicy in every namespace. The documented template is version 1.0.3 and is referential: configure the controller to observe NetworkPolicy objects so the constraint can evaluate them. This is a configuration guardrail, not a replacement for live traffic probes.
Handle DNS as an explicit exception
A default-deny egress policy blocks DNS unless a separate rule allows it. If workloads need DNS, identify the intended resolver and scope the exception to that resolver and the required DNS traffic. Then test both that the intended resolution works and that alternate resolvers or other unapproved outbound destinations remain blocked.
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A broad rule allowing port 53 to any IP may reduce accidental connectivity failures, but it is not equivalent to zero egress. The CNCF’s 2020 guide warns that an attacker may use port 53 as an exfiltration route. DNS permission should therefore be treated as a deliberate egress channel, not as a harmless prerequisite that can be left unrestricted.
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Kubernetes NetworkPolicy provides the basic pod-level isolation and egress rules. Domain-name filtering is implementation-dependent; confirm the API version and behavior supported by the actual cluster rather than assuming every NetworkPolicy implementation can enforce FQDN rules.
The Kubernetes Network Policy API SIG’s NPEP-133 page demonstrates FQDN allowlisting with default deny, including IPv4 and IPv6 deny coverage. Google Kubernetes Engine (GKE) separately documents provider-specific FQDN egress policies and notes that established connections may remain active after a rule is removed until those flows close under connection tracking. These are implementation-specific behaviors, not universal guarantees of Kubernetes NetworkPolicy.
| Control or test | What it can establish | What it does not establish by itself |
|---|---|---|
| Default-deny NetworkPolicy | Selected pods are egress-isolated under a supporting, enforcing network plugin, subject to all applicable policies. | That every policy in the cluster denies egress, or that node and host-network traffic are covered. |
| Policy-as-code constraint | Required policy objects are present according to the constraint’s configured inputs. | That the plugin enforces those objects or that outbound probes fail. |
| Runtime connection probes | Whether tested workloads could establish tested connections at test time. | That untested workloads, paths, destinations, or future states behave identically. |
| FQDN egress policy | Domain-based filtering where the deployed implementation supports it and the tested rules behave as intended. | Portable behavior across providers or automatic termination of existing connections after a rule change. |
Report a bounded result, not a sovereignty guarantee
A defensible test report describes the environment, workload scope, policy state, enforcement implementation, probes, and untested paths. A result might say: “The tested workloads could not establish the tested outbound connections under the recorded policy and platform configuration.” Avoid expanding that finding into a claim that no data can leave any system.
To assess sovereignty, separately establish the relevant requirements and gather evidence about data location, processing, access, and legal governance. The egress tests described here address network connectivity, not those broader questions.
Quick Recap
Source notes
- Kubernetes, “Network Policies” and “NetworkPolicy API limitations and hostNetwork behavior,” documentation accessed 2026-10-07.
- Google Cloud, “Constraint template library: K8sRequireDefaultDenyEgressPolicy,” documentation accessed 2026-10-07; template version 1.0.3.
- Kubernetes Network Policy API SIG, “NPEP-133: FQDN Selector for Egress Traffic,” accessed 2026-10-07.
- Google Cloud, “Control Pod egress traffic using FQDN network policies,” documentation accessed 2026-10-07.
- CNCF, “Guide to Kubernetes egress network policies,” published 2020-02-10.
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