Deployment Config vs Kubernetes Deployment

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Example manifests

apiVersion: apps/v1
kind: Deployment
metadata:
  name: example
  namespace: mikel1992-dev
spec:
  selector:
    matchLabels:
      app: httpd
  replicas: 3
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: >-
          image-registry.openshift-image-registry.svc:5000/openshift/httpd:latest
        ports:
        - containerPort: 8080
---
apiVersion: apps.openshift.io/v1
kind: DeploymentConfig
metadata:
  name: example
  namespace: mikel1992-dev
spec:
  selector:
    app: httpd
  replicas: 3
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: >-
          image-registry.openshift-image-registry.svc:5000/openshift/httpd:latest
        ports:
        - containerPort: 8080

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What does a Deployment do?

• A Deployment is a Kubernetes controller that ensures a desired number of Pods from a Pod template are running.
• You declare the replica count (for example replicas: 3) and the Deployment controller uses a ReplicaSet to maintain that count.
• The Deployment spec contains the Pod template where you define container images, ports, volumes, environment variables, and other container-level settings.
• When you update the Pod template (for example, change the container image), the Deployment controller creates a new ReplicaSet and performs a controlled rollout (rolling update by default).

• kubectl apply -f deployment.yaml
• kubectl rollout status deployment/example
• kubectl rollout history deployment/example

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What does a DeploymentConfig do?

• A DeploymentConfig is conceptually similar: it stores a Pod template and the desired replica count, and its controller creates ReplicationController objects to realize that desired state.
• DeploymentConfig supports OpenShift-specific triggers that can start a new deployment automatically when something changes — for example:
  • imageChange triggers hooked to ImageStreams.
  • configChange triggers when the DeploymentConfig template or strategy changes.
• DeploymentConfig supports several deployment strategies (Rolling, Recreate, Custom), and can be managed via the oc CLI in OpenShift.

• oc apply -f deploymentconfig.yaml
• oc rollout status dc/example
• oc tag / oc import-image (for ImageStream workflows)

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Key differences

• Controller types
  • Kubernetes Deployment → creates ReplicaSets.
  • OpenShift DeploymentConfig → creates ReplicationControllers.
• Selector capabilities
  • ReplicaSet (used by Deployments) supports set-based selector requirements via matchExpressions as well as matchLabels.
  • ReplicationController (used by DeploymentConfig) supports only equality-based selectors (label equality via matchLabels).
• Update/triggers and strategies
  • Deployments perform rollouts (rolling update by default) when the Pod template changes. Kubernetes provides rollout commands (kubectl rollout) and declarative updates (kubectl apply) to manage this.
  • DeploymentConfig supports additional OpenShift triggers (notably imageChange triggers tied to ImageStreams and configChange) that can automatically trigger a new deployment when an ImageStream or config changes. DeploymentConfig also supports multiple deployment strategies (Rolling, Recreate, Custom).

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Quick comparison table

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Recommendation

• Choose Kubernetes Deployments for portability and compatibility with upstream Kubernetes tooling and CI/CD pipelines.
• Choose DeploymentConfig when you require OpenShift-native capabilities: ImageStream-driven workflows, automatic image triggers, or an existing OpenShift Build/Deploy pipeline.

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Summary

• Deployments and DeploymentConfigs both manage Pod templates and scaling.
• They differ in the underlying controller (ReplicaSet vs ReplicationController), selector semantics, and integration with OpenShift features.
• For most use cases, prefer Kubernetes Deployments for portability; use DeploymentConfig when you specifically require OpenShift features.

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Links and references

• Kubernetes Deployments documentation
• OpenShift DeploymentConfig documentation
• OpenShift ImageStreams