UseCases of Kustomize


This is the second article out of three articles on Kubernetes tool : Kustomize. This article covers the usecases. 

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UseCase 1 : Config map generation and secreat generation 
secretGenerator:
- name: myregistrykey
 type: docker-registry
 literals:
 - docker-server=DOCKER_REGISTRY_SERVER
 - docker-username=DOCKER_USER
 - docker-password=DOCKER_PASSWORD
 - docker-email=DOCKER_EMAIL


This is same as: 

kubectl create secret docker-registry myregistrykey --docker-server=DOCKER_REGISTRY_SERVER --docker-username=DOCKER_USER --docker-password=DOCKER_PASSWORD --docker-email=DOCKER_EMAIL

Same as above configMapGenerator

configMapGenerator
- name: profile
  files: 
  - hello.config
  
  
We can also merge two configmaps

configMapGenerator:
- name: my-configmap
  behavior: merge
  files:
  - plumbing.properties
  - secret.properties


Configmap from literals

configMapGenerator:
- name: my-configmap
  literals:
  - foo=bar
  - baz=qux
  
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UseCase 2 : Creating multiple variants using overlays. 
Edit attributes  as per specific file. Here localserv.yaml . Keyword is patchesStrategicMerge

kustomize edit add patch ocalserv.yaml

bases:
- ../../base
patchesStrategicMerge:
- localserv.yaml

Multi Variant Examples: 
https://github.com/kubernetes-sigs/kustomize/blob/master/examples/helloWorld/README.md
https://github.com/kubernetes-sigs/kustomize/blob/master/examples/breakfast.md

we can use "kustomize diff base/variant1/variant2" command to see the difference. 

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UseCase 3 : edit container image and tag

kustomize edit set image busybox=alpine:3.6


images:
- name: busybox
  newName: alpine
  newTag: 3.6
==============================
UseCase 4 : Remote Target
kustomize build can be run on a URL.

The effect is the same as cloning the repo, checking out a particular ref (commit hash, branch name, release tag, etc.), then running kustomize build against the desired directory in the local copy.
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UseCase 5 : applying a JSON patch. Replace and add

cat <$DEMO_HOME/ingress_patch.json
[
  {"op": "replace", "path": "/spec/rules/0/host", "value": "foo.bar.io"},
  {"op": "replace", "path": "/spec/rules/0/http/paths/0/backend/servicePort", "value": 8080}
]
EOF
You can also write the patch in YAML format. This example also shows the "add" operation:

cat <$DEMO_HOME/ingress_patch.yaml
- op: replace
  path: /spec/rules/0/host
  value: foo.bar.io

- op: add
  path: /spec/rules/0/http/paths/-
  value:
    path: '/test'
    backend:
      serviceName: my-test
      servicePort: 8081
EOF


patchesJson6902:
- target:
    group: apps
    version: v1
    kind: Deployment
    name: my-nginx
  path: patch.yaml
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UseCase 6 : Patch on multiple objects
JSON patch and strategic merge patch can be applied to selected resources

patches:
- path: "PatchFile"
  target:
    group: "Group"
    version: "Version"
    kind: "Kind"
    name: "Name"
    namespace: "Namespace"
    labelSelector: "LabelSelector"
    annotationSelector: "AnnotationSelector"
==============================
UseCase 7 : Injecting k8s runtime data into containers

https://github.com/kubernetes-sigs/kustomize/blob/master/examples/wordpress/README.md

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