Express YourSelf !

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

==============================
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

==============================
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.

==============================
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.
==============================
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
==============================
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

Kustomize

This is the first article out of three articles on Kubernetes tool : Kustomize. This article covers the basics.

Kustomize

Kustomize is a CLI for managing K8s style objects with declarative ways

==============================
Edit name attribute by adding prefix/suffix to it

namePrefix: prod-
nameSuffix: "-001"

Edit labels (k,v)

commonLabels:
app: my-wordpress

Edit annotations (k,v)

commonAnnotations:
description: this is test

Edit namespace

namespace: my-namespace
==============================
Edit attribute to Multiple Files.
kustomize edit add resource deployment.yaml
kustomize edit add resource service.yaml

commonLabels:
app: my-wordpress
resources:
- deployment.yaml
- service.yaml
==============================
Edit attribute to Multiple directory.

commonLabels:
app: my-wordpress
bases:
- ./wordpress
- ./mysql
==============================

$ kustomize build $DEV_HOME
Its output is concatenated YAML documents. They can be directed to file or to kubectl

kubectl apply -k $DEV_HOME
kustomize build $DEV_HOME | kubectl apply -f -
kubectl kustomize $DEV_HOME
==============================

Useful Terms

base: A combination of a kustomization and resource(s). Bases can be referred to by other kustomizations.

kustomization: Refers to a kustomization.yaml file, or more generally to a directory containing the kustomization.yaml file and all the relative file paths that the YAML file references.

overlay: A combination of a kustomization that refers to a base, and a patch. An overlay may have multiple bases.

patch: General instructions to modify a resource.

resource: Any valid YAML file that defines an object with a kind and a metadata/name field.

target: The argument to kustomize build. For example, kustomize build $TARGET. A target must be a path or a URL to a kustomization. A target can be a base or an overlay.

variant: The outcome of applying an overlay to a base.

Read More: https://github.com/kubernetes-sigs/kustomize/blob/master/docs/glossary.md

Reference:
https://www.mirantis.com/blog/introduction-to-kustomize-part-1-creating-a-kubernetes-app-out-of-multiple-pieces/
https://www.mirantis.com/blog/introduction-to-kustomize-part-2-overriding-values-with-overlays/
https://github.com/kubernetes-sigs/kustomize
https://kustomize.io/

Other similar tools
https://github.com/kubernetes/community/blob/master/contributors/design-proposals/architecture/declarative-application-management.md
https://docs.google.com/spreadsheets/d/1FCgqz1Ci7_VCz_wdh8vBitZ3giBtac_H8SBw4uxnrsE/edit#gid=0

Life is an exercise to express the InExpressible.

Express YourSelf !

eBPF, OPA, Blackbox exporter, ffwd, Heroic

Easily Observing Operators

Kustomize plugins

UseCases of Kustomize

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