CNCF CKA Bundle

The offered statement is true for this other mechanism: CoreDNS behavior is configured separately from Service definitions, and incorrect DNS plugins or cluster domain can break discovery cluster-wide. It does not explain the facts described here, which follow from: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist.

A ClusterIP Service provides stable in-cluster virtual addressing and directs traffic to selected ready Pod endpoints. That explanation applies to a different technical failure. Here the controlling principle is: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist.

The offered statement is true for this other mechanism: EndpointSlices represent Service backend addresses and readiness; Service existence alone does not prove endpoints exist. It does not explain the facts described here, which follow from: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist.

This observation would test a different technical dependency: A NodePort Service allocates a cluster-configured host port on each node while retaining its cluster IP routing. The current issue is governed by: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist. Its decisive check is “Run kubectl -n kube-system logs deployment/coredns --tail=50 and compare to an in-Pod resolution test”.

The alternative verifies a different condition: Services select matching Pods; an unmatched selector can leave EndpointSlices without usable backends despite healthy Pods. The current case instead depends on: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist. Confirm that “Run kubectl -n kube-system logs deployment/coredns --tail=50 and compare to an in-Pod resolution test”.

This observation would test a different technical dependency: An egress-isolating NetworkPolicy can block Pod outbound connections; DNS and required dependencies need explicit allowances. The current issue is governed by: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist. Its decisive check is “Run kubectl -n kube-system logs deployment/coredns --tail=50 and compare to an in-Pod resolution test”.

The suggested review tracks a different technical risk: The Service port is what clients connect to, while targetPort must reach the actual backend listener. Here the sustained control must address: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist. Choose “Monitor DNS replica readiness, restart trends and upstream resolution errors”.

That safeguard is relevant to: Cluster DNS should resolve Service names inside its configured domain; host-side DNS results do not prove in-cluster resolution. The current failure instead follows from: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist. Its prevention measure is “Monitor DNS replica readiness, restart trends and upstream resolution errors”.

This routine guards against another mechanism: NetworkPolicy egress rules are additive and DNS lookup requires permitted traffic to the DNS server, not only a correct Service record. The recurring exposure in the current case is: DNS resolution may fail when CoreDNS replicas are unhealthy even when the requested Service and Pod endpoints exist. The matching preventive check is “Monitor DNS replica readiness, restart trends and upstream resolution errors”.

The offered action targets: An egress-isolating NetworkPolicy can block Pod outbound connections; DNS and required dependencies need explicit allowances. The case facts point instead to: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Implement “Run kubectl -n ledger apply -f ./policies/invoice-api-deny-ingress.yaml after validating selectors and the CNI's policy enforcement support” to address that specific condition.

The proposed action belongs to the mechanism: An egress-isolating NetworkPolicy can block Pod outbound connections; DNS and required dependencies need explicit allowances. Here the stated fault follows a different mechanism: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The corrective choice is “Run kubectl -n ledger apply -f ./policies/invoice-api-deny-ingress.yaml after validating selectors and the CNI's policy enforcement support”.

The offered action targets: An Ingress resource declares HTTP host/path routing but requires an actual installed Ingress controller. The case facts point instead to: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Implement “Run kubectl -n ledger apply -f ./policies/invoice-api-deny-ingress.yaml after validating selectors and the CNI's policy enforcement support” to address that specific condition.

This principle describes a separate cause: A NodePort Service allocates a cluster-configured host port on each node while retaining its cluster IP routing. The reported condition is governed by: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The two mechanisms should not be conflated.

Gateway API separates infrastructure listener ownership from application route attachments and depends on controller support. That explanation applies to a different technical failure. Here the controlling principle is: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress.

This principle describes a separate cause: An egress-isolating NetworkPolicy can block Pod outbound connections; DNS and required dependencies need explicit allowances. The reported condition is governed by: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The two mechanisms should not be conflated.

The alternative verifies a different condition: An egress-isolating NetworkPolicy can block Pod outbound connections; DNS and required dependencies need explicit allowances. The current case instead depends on: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Confirm that “Run kubectl -n ledger get networkpolicy invoice-api-deny-ingress -o yaml and perform an authorized denied-connection probe”.

That test belongs to another control with this basis: An ingress rule with a podSelector selects source Pods in its own namespace unless combined with other peer selectors. In the current case, the governing reason is: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The direct verification is “Run kubectl -n ledger get networkpolicy invoice-api-deny-ingress -o yaml and perform an authorized denied-connection probe”.

This observation would test a different technical dependency: Gateway API HTTPRoutes express matching and backend behavior while Gateway resources own compatible listeners. The current issue is governed by: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Its decisive check is “Run kubectl -n ledger get networkpolicy invoice-api-deny-ingress -o yaml and perform an authorized denied-connection probe”.

This routine guards against another mechanism: Cluster DNS should resolve Service names inside its configured domain; host-side DNS results do not prove in-cluster resolution. The recurring exposure in the current case is: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The matching preventive check is “Test security policies from allowed and denied sources rather than trusting YAML alone”.

The suggested review tracks a different technical risk: Ingress TLS termination relies on a controller and a referenced TLS Secret; updating a Service alone does not install certificates. Here the sustained control must address: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Choose “Test security policies from allowed and denied sources rather than trusting YAML alone”.

That safeguard is relevant to: An Ingress resource declares HTTP host/path routing but requires an actual installed Ingress controller. The current failure instead follows from: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Its prevention measure is “Test security policies from allowed and denied sources rather than trusting YAML alone”.

This alternative is a response to another technical cause: An Ingress resource declares HTTP host/path routing but requires an actual installed Ingress controller. The reported case instead depends on: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The action that directly addresses it is “Run kubectl -n observability apply -f ./policies/metrics-api-deny-ingress.yaml after validating selectors and the CNI's policy enforcement support”.

The proposed action belongs to the mechanism: Services select matching Pods; an unmatched selector can leave EndpointSlices without usable backends despite healthy Pods. Here the stated fault follows a different mechanism: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The corrective choice is “Run kubectl -n observability apply -f ./policies/metrics-api-deny-ingress.yaml after validating selectors and the CNI's policy enforcement support”.

This alternative is a response to another technical cause: A ClusterIP Service provides stable in-cluster virtual addressing and directs traffic to selected ready Pod endpoints. The reported case instead depends on: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The action that directly addresses it is “Run kubectl -n observability apply -f ./policies/metrics-api-deny-ingress.yaml after validating selectors and the CNI's policy enforcement support”.

A ClusterIP Service provides stable in-cluster virtual addressing and directs traffic to selected ready Pod endpoints. That explanation applies to a different technical failure. Here the controlling principle is: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress.

The offered statement is true for this other mechanism: An egress-isolating NetworkPolicy can block Pod outbound connections; DNS and required dependencies need explicit allowances. It does not explain the facts described here, which follow from: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress.

This principle describes a separate cause: Gateway API HTTPRoutes express matching and backend behavior while Gateway resources own compatible listeners. The reported condition is governed by: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The two mechanisms should not be conflated.

This observation would test a different technical dependency: NetworkPolicy egress rules are additive and DNS lookup requires permitted traffic to the DNS server, not only a correct Service record. The current issue is governed by: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Its decisive check is “Run kubectl -n observability get networkpolicy metrics-api-deny-ingress -o yaml and perform an authorized denied-connection probe”.

The alternative verifies a different condition: Gateway API separates infrastructure listener ownership from application route attachments and depends on controller support. The current case instead depends on: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Confirm that “Run kubectl -n observability get networkpolicy metrics-api-deny-ingress -o yaml and perform an authorized denied-connection probe”.

That test belongs to another control with this basis: An Ingress resource declares HTTP host/path routing but requires an actual installed Ingress controller. In the current case, the governing reason is: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The direct verification is “Run kubectl -n observability get networkpolicy metrics-api-deny-ingress -o yaml and perform an authorized denied-connection probe”.

This routine guards against another mechanism: Services select matching Pods; an unmatched selector can leave EndpointSlices without usable backends despite healthy Pods. The recurring exposure in the current case is: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The matching preventive check is “Test security policies from allowed and denied sources rather than trusting YAML alone”.

That safeguard is relevant to: Gateway API separates infrastructure listener ownership from application route attachments and depends on controller support. The current failure instead follows from: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. Its prevention measure is “Test security policies from allowed and denied sources rather than trusting YAML alone”.

This routine guards against another mechanism: Ingress TLS termination relies on a controller and a referenced TLS Secret; updating a Service alone does not install certificates. The recurring exposure in the current case is: A selecting NetworkPolicy with ingress isolation and no allow rules denies new ingress to selected Pods except protocol-specific policy behavior; it does not itself control egress. The matching preventive check is “Test security policies from allowed and denied sources rather than trusting YAML alone”.