Solution Namespaces optional

This article provides a comprehensive lab walkthrough on namespaces in Kubernetes, addressing questions related to namespaces, pods, and services. Follow the steps below to learn how to manage namespaces effectively.

Identifying the Number of Namespaces

To determine the number of namespaces in your cluster, you can run either of the following commands:

kubectl get namespaces

or its shorthand:

kubectl get ns

The sample output below shows a list of namespaces:

controlplane ~ ✗ kubectl get namespaces
NAME                 STATUS    AGE
default              Active    6m50s
kube-system          Active    6m49s
kube-public          Active    6m49s
kube-node-lease      Active    6m49s
finance              Active    27s
marketing            Active    27s
dev                  Active    27s
prod                 Active    27s
manufacturing        Active    27s
research             Active    27s

And using the shorthand command:

controlplane ~ ✗ kubectl get ns
NAME                 STATUS    AGE
default              Active    6m55s
kube-system          Active    6m54s
kube-public          Active    6m54s
kube-node-lease      Active    6m54s
finance              Active    32s
marketing            Active    32s
dev                  Active    32s
prod                 Active    32s
manufacturing        Active    32s
research             Active    32s

In this example, there are a total of 10 namespaces.

Counting Pods in the Research Namespace

To determine the number of pods running in the research namespace, execute the following command:

kubectl get pods --namespace=research

The output might look like this:

controlplane ~ ⟶ kubectl get pods --namespace=research
NAME      READY   STATUS             RESTARTS   AGE
dna-2     0/1     CrashLoopBackOff   3 (14s ago)   76s
dna-1     0/1     CrashLoopBackOff   3 (16s ago)   76s

Alternatively, you can use the shorthand option:

kubectl get pods -n research

Both commands confirm that there are 2 pods in the research namespace.

Creating a Pod in the Finance Namespace

Before creating a pod in the finance namespace, ensure that the namespace exists by running:

kubectl get namespaces

You should see output similar to:

controlplane ~ ❯ kubectl get namespaces
NAME                 STATUS   AGE
default              Active   6m50s
kube-system          Active   6m49s
kube-public          Active   6m49s
kube-node-lease      Active   6m49s
finance              Active   32s
marketing            Active   32s
dev                  Active   32s
prod                 Active   32s
manufacturing        Active   32s
research             Active   32s

Next, create a Redis pod named "redis" in the finance namespace with the following command:

kubectl run redis --image=redis -n finance

After successfully executing this command, you will see a confirmation message:

pod/redis created

You can verify the pod creation by listing the pods in the finance namespace:

kubectl get pods -n finance

Sample output:

NAME      READY   STATUS            RESTARTS   AGE
payroll   1/1     Running           0          2m20s
redis     0/1     ContainerCreating 0          8s

Locating the Blue Pod's Namespace

To find out which namespace the blue pod is running in, you have two options:

1. Manually inspect each namespace using:

   kubectl get pods -n <namespace>
   

2. List all pods across every namespace with:

   kubectl get pods --all-namespaces
   

The sample output below illustrates pods across namespaces:

NAMESPACE         NAME                                                         READY   STATUS              RESTARTS   AGE
kube-system       local-path-provisioner-6c796847f7-j5sqx                        1/1     Running             0          9m5s
kube-system       coredns-57889956d-bkj56                                       1/1     Running             0          9m5s
kube-system       helm-install-traefik-crd-d2fg7                                0/1     Completed           0          9m
kube-system       metrics-server-7cd5fcbb67-kdgzb                                1/1     Running             1          9m5s
kube-system       helm-install-traefik-c987s                                     2/2     Running             0          8m30s
kube-system       svclb-traefik-jptsh                                           1/1     Running             0          9m5s
marketing         redis-db                                                     1/1     Running             0          3m
dev               redis-db                                                     1/1     Running             0          3m
manufacturing     red-app                                                      1/1     Running             0          3m
finance           payroll                                                      1/1     Running             0          3m
marketing         blue                                                         1/1     CrashLoopBackOff    4 (80s ago)  3m3s
research          dna-1                                                        0/1     CrashLoopBackOff    4 (70s ago)  3m3s
finance           redis                                                        1/1     Running             0          51s

From the output, it is clear that the blue pod is located in the marketing namespace.

Accessing the Database Service from the Blue Application

The blue application, a simple web application for connectivity tests, interacts with a database service. Depending on where the DB service is running, the access method varies.

Accessing the DB Service in the Same Namespace (Marketing)

In the marketing namespace, the blue application and its associated DB service coexist. To check the pods in this namespace, run:

kubectl get pods -n marketing

Expected output:

NAME       READY   STATUS    RESTARTS   AGE
redis-db   1/1     Running   0          4m14s
blue       1/1     Running   0          4m14s

Next, list the services in the marketing namespace:

kubectl get svc -n marketing

This yields an output similar to:

NAME            TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)            AGE
blue-service    NodePort   10.43.82.162   <none>        8080:30082/TCP     4m27s
db-service      NodePort   10.43.134.33   <none>        6379:30758/TCP     4m27s

Since both the blue application and the DB service are in the same namespace, the application can reach the DB service simply by using its DNS name, which is:

db-service

and connecting via port 6379.

Accessing the DB Service in the dev Namespace

Another DB service is running in the dev namespace. To view it, execute:

kubectl get svc -n dev

The output might be as follows:

NAME            TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
db-service      ClusterIP   10.43.252.9     <none>        6379/TCP         5m22s

To access the DB service in the dev namespace from the blue application located in the marketing namespace, you must use the fully qualified DNS name. The DNS naming convention is:

<service-name>.<namespace>.svc.cluster.local

In this case, the DNS name is:

db-service.dev.svc.cluster.local

Using this fully qualified domain name ensures traffic is correctly directed to the DB service in the dev namespace on port 6379.

This concludes the lab solution for namespaces. Each step demonstrates how to manage and interact with namespaces, pods, and services in a Kubernetes cluster.

For more details on Kubernetes concepts, visit the Kubernetes Documentation.