Kubernetesdevops~10 mins

Cross-namespace communication in Kubernetes - Step-by-Step Execution

Choose your learning style9 modes available

Learn Why Deep Visual Try Challenge Project Recall Time

Process Flow - Cross-namespace communication

Pod in Namespace A

↓

Send request to Service in Namespace B

↓

Kubernetes DNS resolves service.ns-b.svc.cluster.local

↓

Request routed to Service in Namespace B

↓

Service forwards to Pod(s) in Namespace B

↓

Pod in Namespace B processes request and responds

A pod in one namespace sends a request to a service in another namespace using the full DNS name, which Kubernetes resolves and routes to the target pod.

Execution Sample

Kubernetes

kubectl run client --image=busybox -n ns-a -- sleep 3600
kubectl exec -n ns-a client -- wget -qO- http://service.ns-b.svc.cluster.local

A pod in namespace 'ns-a' tries to access a service in namespace 'ns-b' using the full DNS name.

Process Table

Step	Action	Command/Request	Result/Output
1	Create pod in ns-a	kubectl run client --image=busybox -n ns-a -- sleep 3600	Pod 'client' running in namespace 'ns-a'
2	Pod in ns-a sends HTTP request	wget -qO- http://service.ns-b.svc.cluster.local	DNS resolves to service IP in ns-b
3	Request routed to service in ns-b	Service forwards request	Request reaches pod(s) behind service in ns-b
4	Pod in ns-b processes request	Pod responds	HTTP response returned to pod in ns-a
5	Pod in ns-a receives response	wget output	<HTML or service response content>
6	Exit	Request complete	Cross-namespace communication successful

💡 Request completes successfully after routing through Kubernetes DNS and service in another namespace

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Pod in ns-a	Not running	Running	Running	Running	Running
DNS resolution	Not done	Resolved to service IP	Resolved	Resolved	Resolved
Request state	None	Sent	Routed	Processed	Response received

Key Moments - 2 Insights

Why do we need to use the full DNS name including the namespace to reach a service in another namespace?

Can a pod in one namespace access a pod directly in another namespace without a service?

Visual Quiz - 3 Questions

Test your understanding

Look at the execution_table, at which step does the DNS resolution happen?

AStep 1

BStep 3

CStep 2

DStep 4

Concept Snapshot

Cross-namespace communication in Kubernetes:
- Pods communicate across namespaces via Services
- Use full DNS name: service.namespace.svc.cluster.local
- Kubernetes DNS resolves and routes requests
- Direct pod-to-pod cross-namespace access is discouraged
- Services provide stable endpoints for cross-namespace access

Full Transcript

In Kubernetes, pods in one namespace can communicate with services in another namespace by using the full DNS name of the service, which includes the service name, namespace, and cluster domain. The flow starts with a pod in namespace A sending a request to a service in namespace B. Kubernetes DNS resolves the full service name to the service's cluster IP in namespace B. The request is routed through the service to the pods behind it in namespace B. The pods process the request and send back a response. This method ensures proper routing and isolation between namespaces. Direct pod-to-pod communication across namespaces is not recommended and usually blocked. Using services and full DNS names is the standard way to enable cross-namespace communication.