Inspect Basic Cluster Resources
In this step, you will inspect basic Kubernetes resources—such as Pods, Deployments, and Services—across all namespaces. By using the -A (or --all-namespaces) flag, you will see how resources are organized throughout the entire cluster. This is an excellent opportunity to introduce and understand the concept of Namespaces in Kubernetes.
Namespaces: Resource Isolation
Namespaces are logical partitions within a Kubernetes cluster that help organize and manage resources. They provide a way to group related objects and apply policies, access controls, and resource quotas at a granular level. By separating resources into different namespaces, you can:
- Improve Organization: Group related workloads (e.g., by project, team, or environment—such as dev, test, and production).
- Enhance Security and Access Control: Restrict which users or service accounts can view or modify resources in a particular namespace.
- Simplify Resource Management: Apply resource limits, network policies, and other cluster-wide configurations more effectively.
When you list resources with the -A (or --all-namespaces) flag, you’ll notice that components belonging to the Kubernetes system reside in the kube-system namespace, which is dedicated to cluster-level infrastructure. User-created applications typically reside in the default namespace or other custom namespaces that you define.
Namespaces and Resources
flowchart LR
%% User interacts with the cluster via kube-apiserver
User((Developer))
User -->|kubectl get pods -A| API[kube-apiserver]
%% Control Plane Subgraph
subgraph ControlPlane[Control Plane]
API
ETCD[etcd]
SCH[kube-scheduler]
CTLM[kube-controller-manager]
end
API --> ETCD
API --> SCH
API --> CTLM
%% kube-system namespace
subgraph kube-system[Namespace: kube-system]
SysDeployment[Deployment: coredns]
SysPod1[Pod: coredns-xxx]
SysService[Service: kube-dns]
SysDeployment --> SysPod1
SysService --> SysPod1
end
%% default namespace (renamed to avoid parse issues)
subgraph defaultNs[Namespace: default]
DefDeployment[Deployment: my-app]
DefPod1[Pod: my-app-pod1]
DefPod2[Pod: my-app-pod2]
DefService[Service: my-app-service]
DefDeployment --> DefPod1
DefDeployment --> DefPod2
DefService --> DefPod1
DefService --> DefPod2
end
%% dev namespace
subgraph dev[Namespace: dev]
DevDeployment[Deployment: dev-app]
DevPod[Pod: dev-app-pod]
DevService[Service: dev-app-service]
DevDeployment --> DevPod
DevService --> DevPod
end
%% Demonstration of communication
API --> kube-system
API --> defaultNs
API --> dev
In the diagram:
- The Control Plane manages the entire cluster, communicating with nodes and controlling workloads.
- Namespaces (such as
kube-system, default, and dev) logically separate resources within the cluster.
kube-system holds system-level components like CoreDNS and kube-dns.default is commonly used for general workloads, here represented by a my-app deployment.dev might represent a development environment, isolated from production workloads.
By viewing resources across all namespaces, you gain a comprehensive understanding of how these logical partitions help maintain an organized and secure cluster.
Examples:
List all pods across all namespaces:
kubectl get pods -A
Example output:
NAMESPACE NAME READY STATUS RESTARTS AGE
kube-system coredns-787d4945fb-j8rhx 1/1 Running 0 20m
kube-system etcd-minikube 1/1 Running 0 20m
kube-system kube-apiserver-minikube 1/1 Running 0 20m
kube-system kube-controller-manager-minikube 1/1 Running 0 20m
kube-system kube-proxy-xb9rz 1/1 Running 0 20m
kube-system kube-scheduler-minikube 1/1 Running 0 20m
kube-system storage-provisioner 1/1 Running 1 (20m ago) 20m
Here, you see all system-related pods running in the kube-system namespace. If you had other deployments or services in different namespaces, they would appear in this list as well, each clearly scoped by their namespace.
List all deployments across all namespaces:
kubectl get deployments -A
Example output:
NAMESPACE NAME READY UP-TO-DATE AVAILABLE AGE
kube-system coredns 1/1 1 1 20m
The coredns deployment resides in the kube-system namespace.
Get a comprehensive view of all resources across all namespaces:
kubectl get all -A
This command displays an overview of pods, services, and deployments across different namespaces, helping you understand how these resources are distributed throughout the cluster.
Key Takeaways:
- Namespaces provide logical isolation and organization within a Kubernetes cluster.
- Different Kubernetes components and resources are organized into specific namespaces (e.g.,
kube-system for core services, default for general workloads, and additional namespaces you create).
- By using
-A to view resources across all namespaces, you gain insight into how your cluster is structured and how namespaces serve as boundaries for resource organization and access control.
By understanding how namespaces function as logical environments, you can better navigate, isolate, and manage your workloads and related cluster resources, especially as you scale your deployments and introduce more complexity into your Kubernetes environment.
