Kubernetes Namespaces

Putting every team and environment in one shared space causes name collisions, no isolation, and no way to scope quotas or access. We need logical boundaries inside a single physical cluster.

Solution: Partition the cluster into namespaces (dev/staging/prod) for isolation, resource quotas, and scoped RBAC.

A big port leases out separate sections, one to each tenant company, and each tenant hangs its own signage inside its patch. Two tenants can both post a sign reading Pier 7 because each sign only means something within that company's leased section, so the names never collide. Kubernetes namespaces work the same way: each is a leased section of the cluster where a Service named web in dev and another Service named web in prod can coexist without clashing.

The same cluster entities appear in every day's notes; the <== marks what this day touches.

A virtual cluster inside a cluster — a logical boundary to group and isolate resources (pods, services, configmaps...). Great for separating teams/envs.

A fresh cluster ships with four namespaces, each with a job.

   default          -> where your objects go if none specified
   kube-system      -> control-plane components (coredns, proxy...)
   kube-public      -> world-readable cluster info
   kube-node-lease  -> node heartbeat lease objects

• Isolation: same names in different namespaces don't clash.
• Access control: scope RBAC roles per namespace.
• Resource quotas: cap CPU/memory per namespace.
• Organization: group by team / environment / app.

The core commands for creating namespaces and scoping kubectl to one with -n.

kubectl get ns                                  # list namespaces
kubectl create namespace dev                    # create
kubectl get pods -n dev                          # list pods in ns
kubectl get pods --all-namespaces               # everything (-A)
kubectl run nginx --image=nginx -n dev          # create in ns

# set default ns for current context (stop typing -n)
kubectl config set-context --current --namespace=dev

Set metadata.namespace to pin an object to a specific namespace instead of default.

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  namespace: dev        # <- pin the object to a namespace
spec:
  containers:
    - name: nginx
      image: nginx

The demo runs the same nginx workload twice, once per namespace, each fronted by its own service. It shows isolation and how to cross the boundary.

• svc-test lives in default and load-balances the 3 nginx pods there.
• svc-demo lives in demo and load-balances the 3 nginx pods there.
• Both services can be named the same kind of thing without clashing — names are unique per namespace, so the two never collide.
• A pod in default hitting svc-test uses the short name (same namespace).
• To reach across, a pod in default calls svc-demo by its FQDN, and a pod in demo calls svc-test by its FQDN. The arrow crossing the boundary in the diagram is exactly this cross-namespace call.

kubectl create namespace demo
kubectl run nginx --image=nginx -n default          # x3 -> behind svc-test
kubectl run nginx --image=nginx -n demo             # x3 -> behind svc-demo
kubectl expose pod nginx --name=svc-test -n default --port=80
kubectl expose pod nginx --name=svc-demo -n demo   --port=80

# from a pod in default:
curl svc-test                                       # short name, same ns
curl svc-demo.demo.svc.cluster.local                # FQDN, cross ns

Each service still gets its own ClusterIP; the FQDN just resolves to that IP through CoreDNS. Namespaces don't block traffic by default — they scope names, not the network (that's what NetworkPolicies are for).

A pod reaches a service in another namespace by using its fully-qualified DNS name; same-namespace calls can use the short name.

   same ns:   curl web
   other ns:  curl web.dev.svc.cluster.local
              <service>.<namespace>.svc.cluster.local

A ResourceQuota caps how much CPU, memory, and how many objects a namespace can consume.

apiVersion: v1
kind: ResourceQuota
metadata:
  name: dev-quota
  namespace: dev
spec:
  hard:
    pods: "10"
    requests.cpu: "2"
    requests.memory: 2Gi

Some objects are cluster-scoped (not in any namespace):

   nodes, namespaces, persistentvolumes, clusterroles
   check: kubectl api-resources --namespaced=false

Namespaces scope names and access, and a call into another namespace uses the fully qualified DNS name.

• Namespaces = logical isolation within one cluster.
• Names are unique per namespace, not cluster-wide.
• Use -n <ns> / -A, and cross-ns DNS = svc.ns.svc.cluster.local.

• [ ] Created a namespace and ran a pod in it
• [ ] Listed resources with -n and -A
• [ ] Set a default namespace on the context
• [ ] Reached a service across namespaces by FQDN