Kubernetes/Kustomize

Kustomize

• kubectl+kustomize SIG CLI

kustomize lets you customize raw, template-free YAML files for multiple purposes, leaving the original YAML untouched and usable as is.

Install

# Detects your OS and downloads kustomize binary to cwd
curl -s "https://raw.githubusercontent.com/kubernetes-sigs/kustomize/master/hack/install_kustomize.sh"  | bash

# Install on Linux - option2
VERSION=v4.1.2
VERSION=$(curl --silent "https://api.github.com/repos/kubernetes-sigs/kustomize/releases" | jq -r '.[].tag_name | select(. | contains("kustomize"))' | sort | tail -1 | cut -d"/" -f2); echo $VERSION
curl -L https://github.com/kubernetes-sigs/kustomize/releases/download/kustomize%2F${VERSION}/kustomize_${VERSION}_linux_amd64.tar.gz -o kustomize_${VERSION}_linux_amd64.tar.gz
tar xzvf kustomize_${VERSION}_linux_amd64.tar.gz
sudo install ./kustomize /usr/local/bin/kustomize

kustomize version --short
{kustomize/v4.1.2  2021-04-15T20:38:06Z  }

Kustomize build workflow

• kustomize vars - use envsubst instead

$ kustomize build ~/target

1. load universal k8s object descriptions
2. read kustomization.yaml from target
3. kustomize bases (recurse 2-5)
4. load and/or generate resources
5. apply target's kustomization operations
6. fix name references
7. emit yaml

= kustomize.yaml A build stage first

• processes resources,
• then it processes generators, adding to the resource list under consideration,
• then it processes transformers to modify the list,
• and finally runs validators to check the list for whatever error.

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
- {pathOrUrl}
- what resources you want to customize 

# cross-cutting fields
namespace: custom
namePrefix: dev-
nameSuffix: "-svc"
commonLabels:
  app: web
commonAnnotations:
  value: app

generators:
- {pathOrUrl}
- what new resources should be created.
generatorOptions:
  disableNameSuffixHash: true
  labels:
    env: prod
  annotations:
    app: custom

transformers:
- {pathOrUrl}
- what to transform in above mentioned resources

validators:
- {pathOrUrl}
- ...

Patches

patchStrategicMerge

Kubernetes supports a customized version of JSON merge patch called strategic merge patch. This patch format is used by kubectl apply, kubectl edit and kubectl patch, and contains specialized directives to control how specific fields are merged.

Example 101

Note: Bases have been deprecated in v2.1.0 resources-expanded-bases-deprecated

• Kustomize builder note that it operates on the 1st yaml document

Example 101 - environment type overrides

base/kustomization.yaml	overlays/dev/kustomization.yaml	overlays/prod/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1 kind: Kustomization commonLabels: app: sonarqube resources: - gateway.yaml - virtual-service.yaml	apiVersion: ... kind: Kustomization patches: - gateway_patch.yaml - virtual-service_patch.yaml resources: - ../../base	apiVersion: ... kind: Kustomization patches: - gateway_patch.yaml - virtual-service_patch.yaml resources: - ../../base

.
├── base
│   ├── gateway.yaml
│   ├── kustomization.yaml
│   └── virtual-service.yaml
└── overlays # more contextual this directory could be called 'environments'
    ├── dev
    │   ├── gateway_patch.yaml
    │   ├── kustomization.yaml
    │   └── virtual-service_patch.yaml
    └── prod
        ├── gateway_patch.yaml
        ├── kustomization.yaml
        └── virtual-service_patch.yaml

# Build kuctomized output
kustomize version --short # -> {kustomize/v3.8.2  2020-08-29T17:44:01Z  }
kustomize build overlays/dev # apply patches
kustomize build base         # run common functions (as described in base/kustomize.yaml) against the whole code base

What happens?

1. kustomize build overlays/dev finds kustomization.yaml, that describes:
   1. patches: [gateway_patch.yaml, virtual-service_patch.yaml] to be used over the base resources: [../../base]. There are 3 type of patches: patches, patchesStrategicMerge, patchesJson6902 to choose from
2. overlays/dev/kustomization.yaml cascades to the base (source of manifests to be changed) via directive resources: ["../../base"]
3. The base directory contains and runs its own kustomization.yaml file.
4. The base/kustomization.yaml contains common operations, eg. commonLabels, namePrefix functions to be applied to whole code base.
5. Then patch file(s) are applied eg. gateway_patch.yaml contains enough information to identify a resource/object and apply changes.

So, what happens

# Applying the patch: overlays/dev/gateway_patch.yaml 
apiVersion: networking.istio.io/v1beta1
kind: Gateway
metadata:
  name: sonarqube 
spec:
  servers:
  - port:
      number: 443
      name: http
      protocol: HTTP
    hosts:
     - sonarqube-dev.acme.com # <- override
#   | 
#   | over the base
#   v 

# base/gateway.yaml
apiVersion: networking.istio.io/v1beta1
kind: Gateway
metadata:
  labels:
    app: sonarqube
  name: sonarqube
spec:
  selector:
    istio: ingressgateway
  servers:
  - hosts:
    - sonarqube.acme.com
    port:
      name: http
      number: 443
      protocol: HTTP
#   | 
#   | results with
#   v 

apiVersion: networking.istio.io/v1beta1
kind: Gateway
metadata:
  labels:
    app: sonarqube
    owner: piotr # <- label added by base kustomize.yaml fn
  name: sonarqube
spec:
  selector:
    istio: ingressgateway
  servers:
  - hosts:
    - sonarqube-dev.acme.com # <- patch override
    port:
      name: http
      number: 443
      protocol: HTTP

Check yourselves

#         __unchanged manifest_    _base kustomization_    ___patch overlay____________
vimdiff <(cat base/gateway.yaml) <(kustomize build base) <(kustomize build overlays/dev)

Cheatsheet

• Helm charts - last mile

Patch multiple objects

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - ../base

patches:
  - path: patch.json
    target:
      kind: PersistentVolume
      version: v1
      group: ""
      name: volume-(data|master)-\d # regex match
      labelSelector: |
        app.kubernetes.io/component=storage,
        app.kubernetes.io/name=elasticsearch

Delete an object from the base

Strategic Merge Patch provides some patch options like replace, merge, and delete. The simple 'patch' can only patch (manipulate) it.

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - ../base

patchesStrategicMerge:
- |-
  apiVersion: v1
  kind: Namespace
  metadata:
    name: unwanted-namespace
  $patch: delete

secretGenerator

Secrets can be generated from environment variables. Within a template file there is a list of variables, where the variable will become a key and it's value the value.

Environment variable secret template

GIT_USERNAME
GIT_PASSWORD
GIT_CREDENTIALS

Kustomization

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

secretGenerator:
  - name: argocd-git-secret
    envs:
      - git.env
    options:
      disableNameSuffixHash: true

Known issues

• commonLabels altering podSelector.matchLabels and Allow excluding some label selectors from commonLabels

In some settings it makes sense for commonLabels to be included in selectors, and in some settings it doers not make sense to include them in selectors. Kustomize includes by default, and there is no way to opt out. As workaround, you can convert matchLabels to matchExpressions and Kustomize won't touch them. API docs

- podSelector:
      matchLabels:
        app: mongodb-backup

is equivalent with

- podSelector:
      matchExpressions:
        - key: app
        operator: In
        values:
          - mongodb-backup

and Kustomize will keep its hands off.

Resources

• Replacement transform is deprecating Vars
• Kustomize sig
• v3.7.0+ Components
• Glossary
• Kustomization File Fields
• Kustomize - examples kubectl.docs.kubernetes.io
• Kustomize structure_directories
• reference Good!
• inlinePatch
• kustomization of a helm chart