Kustomise Problem Statement & Idealogy

  • What problems does Kustomise try to address.

  • We have three environments:

    • dev

    • stg

    • prod

  • We want to customise the deployment, so it behaves a little differently in each environment.

  • The manifest is the following: 
    apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
spec:
replicas: 1
selector:
  matchLabels:
    component: nginx
template:
  metadata:
    labels:
      component: nginx
  spec:
    containers:
      - name: nginx
        image: nginx

  • For example, we want to change the amount of replicas in the dev environment.

  • How do we modify it on a per configuration basis.

    • A simple solution is to create three separate directories, one for each variation of the above yaml file.

    • stg directory would have replicas set to 2, prod would be 3 etc.

    • To push the changes out, run kubectl apply -f dev/ for all three environments.

    • Not the most optimal or scaleable solution.

      • If create service.yaml file, this is needed to be copied to all directories.

        • Kustomise helps to customise individual environments, without replicating code.

  • Kustomise has two terms - base config and overlay.

    • base config is identical across all environments.

      • This also includes default values, which you can override later on.

      • An example config is the nginx config listed above.

    • overlays - these allow us to customise behaviour on a per-environment basis.

      • An example of an overlay is: 
        spec:
replicas: 1

    • The above overlay would be dev.

      • The overlay changes what is in the base config. In the above example, we focus on replicas.

    • An overlay for stg for example:

        spec:
replicas: 1

  • The directory structure is like so:

    • k8s –> base / overlays

      • Under base you would have:

        • kustomizaton.yaml

        • nginx-depl.yaml

        • service.yaml

        • redis-depl.yaml

      • Under overlays you have:

        • dev –> kustomization.yaml and config-map.yaml

        • stg –> kustomization.yaml and config-map.yaml

        • prod –> kustomization.yaml and config-map.yaml

  • base is shared across all environments. overlay is changes to specific environments.

  • kustomise takes the base and overlay and mixes them together to create the final manifest.

  • kustomise comes built-in with kubectl.

    • May want to install kustomize cli, as the one that comes with kubectl is not the latest version.

  • With kustomize, no need to learn a templating language like helm.

    • Complex helm charts are difficult to read because of the templating system.
  • kustomize is yaml only.

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