Can a Kubernetes Deployment be done from an OpenShift Template file?

Question

I am using OpenShift 4.7 and I want to convert my OpenShift DeploymentConfigs to Kubernetes Deployments. Right now, I'm creating most of my applications with an OpenShift kind: Template file. Do OpenShift Templates support Kubernetes Deployments or do I need to switch to another kind of tool if I want to use Kubernetes Deployments?

Because of the limited information around this, I just tried to convert it to see what would happen and I couldn't get it to work. If someone could shed light on this subject and where to find good examples of how to go from DeploymentConfigs to Deployments I think the internet and I would appreciate that.

One of my current OpenShift DeploymentConfigs looks like this within a Template file:

...
- apiVersion: v1
  kind: DeploymentConfig
  metadata:
    annotations:
      description: Defines how to deploy the database
      template.alpha.openshift.io/wait-for-ready: 'true'
    name: postgresql
  spec:
    replicas: 1
    selector:
      name: postgresql
    strategy:
      type: Recreate
    template:
      metadata:
        labels:
          name: postgresql
        name: postgresql
      spec:
        containers:
        - env:
          - name: POSTGRESQL_USER
            valueFrom:
              secretKeyRef:
                key: database-user
                name: ${NAME}
          - name: POSTGRESQL_PASSWORD
            valueFrom:
              secretKeyRef:
                key: database-password
                name: ${NAME}
          - name: POSTGRESQL_DATABASE
            value: ${DATABASE_NAME}
          image: ' '
          livenessProbe:
            exec:
              command:
              - /usr/libexec/check-container
              - --live
            initialDelaySeconds: 120
            timeoutSeconds: 10
          name: postgresql
          ports:
          - containerPort: 5432
          readinessProbe:
            exec:
              command:
              - /usr/libexec/check-container
            initialDelaySeconds: 5
            timeoutSeconds: 1
          resources:
            limits:
              memory: ${MEMORY_POSTGRESQL_LIMIT}
          volumeMounts:
          - mountPath: /var/lib/pgsql/data
            name: postgresql-data
        volumes:
        - name: postgresql-data
          persistentVolumeClaim:
            claimName: postgresql
    triggers:
    - imageChangeParams:
        automatic: true
        containerNames:
        - postgresql
        from:
          kind: ImageStreamTag
          name: postgresql:${POSTGRESQL_VERSION}
          namespace: ${NAMESPACE}
      type: ImageChange
    - type: ConfigChange
...

You wouldn't be able to just change "DeploymentConfig" -> "Deployment" in the template since they're entirely different objects with a different API. I would recommend comparing your DeploymentConfig to the k8s API reference doc for Deployment: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.19/#deployment-v1-apps — Will Gordon, Jun 25 '21 at 21:20
Thank you, Will. Are you saying that a Kubernetes Deployment cannot be done from a Template file if the fields have been properly converted from the DeploymentConfig? — jontrossbach, Jun 25 '21 at 21:51
A "Deployment" itself should work fine in an OpenShift template. It's purely just a GoLang templating system that makes it easy to define all the needed objects together in a single package (think of it as a Helm alternative). I only meant to imply (as answered below), that a Deployment and DeploymentConfig have different definitions. So if you're _only_ changing the "kind" within your template and nothing else, I would expect this to fail. — Will Gordon, Jun 28 '21 at 16:02

score 0 · Answer 1 · answered Jun 26 '21 at 07:29

according to the official OpenShift documentation there is no reason why you shouldn't be able to template deployments.

However, deploymentConfigs and Deployments are not the same. So simply changing the apiVersion and kind to match deployments might lead to yaml that is not understandable by OpenShift.

For example the DeploymentConfig you provided contains a 'triggers' section. Triggers are available for DeploymentConfigs but not for Deployments.

On a side note: openshift templates are still a thing, however you should thinkg about using a different more widespread templating tool like helm v3. It is more commonly used, can be applied to OpenShift and plain Kubernetes clusters (assuming there are only plain kubernetes ressource types/crd's in that helm chart).

score 0 · Answer 2 · answered Jun 29 '21 at 18:15

The answer is yes but you will have to come up with your own solution for things like triggers and git hooks for now. The conversion from the above DeploymentConfig looked like the following for me:

...
- apiVersion: v1
  kind: Deployment
  metadata:
    annotations:
      deployment.kubernetes.io/revision: '4'
      image.openshift.io/triggers: |-
        [
          {
            "from": {
              "kind": "ImageStreamTag",
              "namespace": "openshift",
              "name": "openshift/postgresql:10"
            },
            "fieldPath": "spec.template.spec.containers[0].image"
          }
        ]
    selfLink: /apis/apps/v1/namespaces/abigail-discourse-project-1/deployments/postgresql
    name: postgresql
    #namespace: ${openshift.project()}
  spec:
    replicas: 1
    selector:
      matchLabels:
        app: postgresql
    template:
      metadata:
        creationTimestamp: null
        labels:
          app: postgresql
      spec:
        containers:
          - resources: {}
            readinessProbe:
              exec:
                command:
                  - /usr/libexec/check-container
              initialDelaySeconds: 5
              timeoutSeconds: 1
              periodSeconds: 9
              successThreshold: 1
              failureThreshold: 3
            terminationMessagePath: /dev/termination-log
            name: postgresql
            livenessProbe:
              exec:
                command:
                  - /usr/libexec/check-container --live
              initialDelaySeconds: 120
              timeoutSeconds: 1
              periodSeconds: 15
              successThreshold: 1
              failureThreshold: 3
            env:
              - name: POSTGRESQL_DATABASE
                value: discourse
              - name: POSTGRESQL_USER
                valueFrom:
                  secretKeyRef:
                    name: discourse
                    key: database-user
              - name: POSTGRESQL_PASSWORD
                valueFrom:
                  secretKeyRef:
                    name: discourse
                    key: database-password
            ports:
              - containerPort: 5432
                protocol: TCP
            imagePullPolicy: Always
            envFrom:
              - secretRef:
                  name: discourse
            image: >-
              image-registry.openshift-image-registry.svc:5000/openshift/postgresql:10
        restartPolicy: Always
    strategy:
      type: Recreate
...

Can a Kubernetes Deployment be done from an OpenShift Template file?

2 Answers2