container.training/slides/k8s/kustomize.md

Kustomize

• Kustomize lets us transform YAML files representing Kubernetes resources

• The original YAML files are valid resource files

  (e.g. they can be loaded with kubectl apply -f)

• They are left untouched by Kustomize

• Kustomize lets us define overlays that extend or change the resource files

---

Differences with Helm

• Helm charts use placeholders {{ like.this }}

• Kustomize "bases" are standard Kubernetes YAML

• It is possible to use an existing set of YAML as a Kustomize base

• As a result, writing a Helm chart is more work ...

• ... But Helm charts are also more powerful; e.g. they can:

  • use flags to conditionally include resources or blocks

  • check if a given Kubernetes API group is supported

  • and much more

---

Kustomize concepts

• Kustomize needs a kustomization.yaml file

• That file can be a base or a variant

• If it's a base:

  • it lists YAML resource files to use

• If it's a variant (or overlay):

  • it refers to (at least) one base

  • and some patches

---

An easy way to get started with Kustomize

• We are going to use Replicated Ship to experiment with Kustomize

• The Replicated Ship CLI has been installed on our clusters

• Replicated Ship has multiple workflows; here is what we will do:

  • initialize a Kustomize overlay from a remote GitHub repository

  • customize some values using the web UI provided by Ship

  • look at the resulting files and apply them to the cluster

---

Getting started with Ship

• We need to run ship init in a new directory

• ship init requires a URL to a remote repository containing Kubernetes YAML

• It will clone that repository and start a web UI

• Later, it can watch that repository and/or update from it

• We will use the jpetazzo/kubercoins repository

  (it contains all the DockerCoins resources as YAML files)

---

ship init

.exercise[

• Change to a new directory:

  mkdir ~/kustomcoins
  cd ~/kustomcoins
  

• Run ship init with the kustomcoins repository:

  ship init https://github.com/jpetazzo/kubercoins
  

]

---

Access the web UI

• ship init tells us to connect on localhost:8800

• We need to replace localhost with the address of our node

  (since we run on a remote machine)

• Follow the steps in the web UI, and change one parameter

  (e.g. set the number of replicas in the worker Deployment)

• Complete the web workflow, and go back to the CLI

---

Inspect the results

• Look at the content of our directory

• base contains the kubercoins repository + a kustomization.yaml file

• overlays/ship contains the Kustomize overlay referencing the base + our patch(es)

• rendered.yaml is a YAML bundle containing the patched application

• .ship contains a state file used by Ship

---

Using the results

• We can kubectl apply -f rendered.yaml

  (on any version of Kubernetes)

• Starting with Kubernetes 1.14, we can apply the overlay directly with:

  kubectl apply -k overlays/ship
  

• But let's not do that for now!

• We will create a new copy of DockerCoins in another namespace

---

Deploy DockerCoins with Kustomize

.exercise[

• Create a new namespace:

  kubectl create namespace kustomcoins
  

• Deploy DockerCoins:

  kubectl apply -f rendered.yaml --namespace=kustomcoins
  

• Or, with Kubernetes 1.14, you can also do this:

  kubectl apply -k overlays/ship --namespace=kustomcoins
  

]

---

Checking our new copy of DockerCoins

• We can check the worker logs, or the web UI

.exercise[

• Retrieve the NodePort number of the web UI:

  kubectl get service webui --namespace=kustomcoins
  

• Open it in a web browser

• Look at the worker logs:

  kubectl logs deploy/worker --tail=10 --follow --namespace=kustomcoins
  

]

Note: it might take a minute or two for the worker to start.