container.training/slides/kube/namespaces.md

Namespaces

• We cannot have two resources with the same name

--

• We cannot have two resources of the same type with the same name

  (But it's OK to have a rng service, a rng deployment, and a rng daemon set)

--

• We cannot have two resources of the same type with the same name in the same namespace

  (But it's OK to have e.g. two rng services in different namespaces)

--

• In other words: the tuple (type, name, namespace) needs to be unique

  (In the resource YAML, the type is called Kind)

---

Pre-existing namespaces

• If we deploy a cluster with kubeadm, we have three namespaces:

  • default (for our applications)

  • kube-system (for the control plane)

  • kube-public (contains one secret used for cluster discovery)

• If we deploy differently, we may have different namespaces

---

Creating namespaces

• We can create namespaces with a very minimal YAML, e.g.:

      kubectl apply -f- <<EOF
      apiVersion: v1
      kind: Namespace
      metadata:
        name: blue
      EOF
  

• If we are using a tool like Helm, it will create namespaces automatically

---

Using namespaces

• We can pass a -n or --namespace flag to most kubectl commands:

  kubectl -n blue get svc
  

• We can also use contexts

• A context is a (user, cluster, namespace) tuple

• We can manipulate contexts with the kubectl config command

---

Creating a context

• We are going to create a context for the blue namespace

.exercise[

• View existing contexts to see the cluster name and the current user:

  kubectl config get-contexts
  

• Create a new context:

  kubectl config set-context blue --namespace=blue \
      --cluster=kubernetes --user=kubernetes-admin
  

]

We have created a context; but this is just some configuration values.

The namespace doesn't exist yet.

---

Using a context

• Let's switch to our new context and deploy the DockerCoins chart

.exercise[

• Use the blue context:

  kubectl config use-context blue
  

• Deploy DockerCoins:

  helm install dockercoins
  

]

In the last command line, dockercoins is just the local path where we created our Helm chart before.

---

Viewing the deployed app

• Let's see if our Helm chart worked correctly!

.exercise[

• Retrieve the port number allocated to the webui service:

  kubectl get svc webui
  

• Point our browser to http://X.X.X.X:3xxxx

]

Note: it might take a minute or two for the app to be up and running.