Namespace

What is Namespace?

Namespace used to isolate the resources within a single cluster. Therefore, each namespace can have its own policies, permissions (RBAC), resource control, etc. In other words, it is used to isolate the users' accessibility.

By default, Kubernetes will automatically create 4 default namespaces:

default
- This is the namespace you can start to deploy the resources without creating a new namespace, when you start using the new cluster.
kube-system
- This is the namespace for objects created by the Kubernetes system for itsa internal purpose, for example, kube-dns, kube-proxy, kubernetes-dashboard, ingresses, etc.
kube-public
- Basically this namespace contains the resources that is readable and visible publicly by all users without any authentication.
- Mostly reserved for cluster usage. kubectl cluster-info
- It contains a single ConfigMap object, basically the cluster info is mainly used for aids discovery and security bootstrap. kubectl get configmap -n kube-public
kube-node-lease
- This namespace holds Lease objects associated with each node. That means node leases will allow the kubelet to send heartbeats so that the control plane (Master Node <- Node controller) can detect node failure.
- Basically this namespace related to cluster scaling.

Namespace usage

Commands

kubectl get <resource> -n <namespace-name>
kubectl get <resource> --namespace=<namespace-name>
kubectl get <resource> --all-namespaces
 
# example
kubectl get pods -n dev
 
# create namespace
kubectl create namespace dev

Switch namespace in current context permanently

If we want to switch to other namespace permanently, we can do the following commands, so that we don't have to specify the namespace option.

kubectl config set-context $(kubectl config current-context) --namespace=<namespace-name>
 
kubectl get <resource> # it will by default show your namespace environment resources

Context is a set of access parameters that define a cluster, namespace, and user in Kubernetes. They actually stored in YAML file kubeconfig, and are used to manage multiple clusters or environments from the same management system.

Create a namespace in YAML

apiVersion: v1
kind: Namespace
metadata:
  name: dev

Use namespace in resources YAML

apiVersion: v1
kind: Pod
metadata:
  name: sample-nginx-pod
  namespace: dev
spec:
  containers:
    - name: nginx
      image: nginx

Connect to other namespace services

If you want to connect to other namespace services, then you have to reference the DNS of the respective namespace, as a DNS entry will automatically added in this format when the service is created. Here is the format;

Format: <service-name>.<namespace>.svc.cluster.local
Example: db-svc.prod.svc.cluster.local
- cluster.local = default domain name of the Kubernetes cluster

Resource quota for namespace

You can limit the resources to be used within a namespace. You can set each namespace with a guaranteed amount and not use more than the limit.

resource-quota.yaml

apiVersion: v1
kind: ResourceQuota
metadata:
  name: quota
  namespace: dev
spec:
  hard:
    pods: "15" # total pods cannot exceed 15
    requests.cpu: "2" # total CPU requests cannot exceed 2 cores
    requests.memory: 2Gi # total memory requests cannot exceed 2Gi
    limits.cpu: "4" # total CPU limits cannot exceed 4 cores
    limits.memory: 4Gi # total memory limits cannot exceed 4Gi

In this case, this dev namespace can only create a maximum of 15 pods. Each pod in the dev namespace will have 2 CPUs and 2G of memory, while the maximum CPU and memory limits are 4 and 4G, respectively.

Limit range for namespace

You can also set the default minimum and maximum limits for the resources like CPU and memory for pods in the namespace. With this setup, we can ensure that all the pods created in the namespace will have the same limits. Remember, if you just create or change a limit range, it will not affect the existing pods.

cpu-limit-range.yaml

apiVersion: v1
kind: LimitRange
metadata:
  name: cpe-resource-constraint
spec:
  limits:
    - default: # specify the default limits for containers
        cpu: 500m
        memory: 512Mi
      defaultRequest: # specify the default request for containers
        cpu: 500m
        memory: 512Mi
      max: # Specify the maximum limit for containers
        cpu: "1"
        memory: 1Gi
      min: # Specify the minimum limit for containers
        cpu: 100m
        memory: 256Mi
      type: Container

With this setup, we specify the default CPU and memory limits for the pods in the namespace are 500m and 512Mi, respectively. The default request for CPU and memory are also set to 500m and 512Mi, respectively.

max - the maximum limit for CPU and memory that can be set on a container
min - the minimum limit for CPU and memory that can be set on a container

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