OpenShift 4.6 Automation and Integration: Kubernetes vs OpenShift, Kustomize and Image Streams

Kubernetes vs OpenShift

https://access.redhat.com/documentation/en-us/openshift_container_platform/4.6/html-single/applications/index#what-deployments-are

Kubernetes	OpenShift
Namespace	Project
Ingress	Route
Deployment Emphasizes availability over consistency. Uses ReplicaSets that support set-based match selectors. Red Hat recommends using Deployments unless you need specific DeploymentConfigs feature.	DeploymentConfig Emphasizes consistency over availability.
Kustomize	Template

$ kubectl create -f hello.yml

$ kubectl apply -f hello.yml

$ kubectl get ingresses.v1.networking.k8s.io

Kustomize

A kustomization is a directory containing a kustomization.yml file.

https://kubernetes.io/docs/tasks/manage-kubernetes-objects/kustomization/

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

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - mydeployment.yaml
images:
  - name: image
    newName: new-image
    newTag: new-tag

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - mydeployment.yaml
secretGenerator:
  - name: mycert
    namespace: openshift-config
    files:
      - tls.crt=my-priv-cert.crt
      - tls.key=my-priv-cert.key
generatorOptions:
  disableNameSuffixHash: true

A kustomization without a bases field is a base.

An overlay includes all resources in its bases.

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
bases:
  - path-to-kustomization

Validate your Kustomize configurations.

$ oc kustomize kustomize_folder

$ oc apply --dry-run -k config

Apply your Kustomize configurations.

$ kubectl apply -k directory_name

Image Streams

Image streams use a unique SHA256 identifier instead of a mutable image tag. This is more robust since image tags (:latest or :v1.1) can change without further notice.

https://access.redhat.com/documentation/en-us/openshift_container_platform/4.6/html-single/images/index#managing-image-streams

Annotating Deployments with Image Stream Triggers

Key: image.openshift.io/triggers
Value:
[
 {
   "from": {
     "kind": "ImageStreamTag",
     "name": "example:latest",
     "namespace": "myapp"
   },
   "fieldPath": "spec.template.spec.containers[?(@.name==\"web\")].image",
   "paused": false
 },
 ...
]

$ skopeo copy \
  docker://quay.io/redhattraining/versioned-hello:v1.0 \
  docker://quay.io/your_account/versioned-hello:latest
  
$ oc get imagestreams

Import image and create image streams and set periodically scheduled (--scheduled) imports to get latest updates.

$ oc import-image quay.io/your_account/versioned-hello:latest --confirm --scheduled

$ oc set triggers deployment/hello --from-image versioned-hello:latest -c hello