Kubernetes: Deployments

Useful links

• https://kubernetes.io/docs/concepts/workloads/controllers/​deployment/
• Also check out my previous posts on:
  • Kubernetes: Pods
  • Kubernetes: ReplicaSets

Concepts

Deployments manage the deployment and scaling of a set of Pods and provide declarative updates to applications.

• A Deployment is described as a set of identical Pods with no unique identities. A Deployment runs multiple replicas of your application and automatically replaces any instances that fail or become unresponsive.
• In essence, Deployments are higher-level concepts that manage ReplicaSets and provide additional features like rolling updates and rollbacks.
• As such, it’s recommended to use Deployment instead of directly managing ReplicaSets because it provides additional useful features.
• Deployments manage stateless applications, while StatefulSets manage stateful applications

Notes

Declarative manifest

• Simple example of Deployment yaml definition, you will find this very similar to ReplicaSet

  apiVersion: apps/v1
  kind: Deployment
  metadata:
    name: nginx-deployment
    labels:
      app: nginx
  spec:
    strategy: # how to replace old pods with new ones
      type: RollingUpdate # default strategy
      rollingUpdate:
        maxUnavailable: 1
        maxSurge: 1
    replicas: 3 # number of replica pods
    selector:
      matchLabels:
        app: nginx # selector
    template: # pod template (just like what we would define in pod yaml)
      metadata:
        labels:
          app: nginx # label of pod
      spec:
        containers:
        - name: nginx
          image: nginx:1.14.2
  

Imperative commands

• Get deployment details
  k get deploy <deployment-name> -o wide
• Update Deployment replicas
  k scale deployment <deployment-name> --replicas=<num>
• Rollback to an earlier Deployment revision
  k rollout undo deploy <deployment-name>
• View the rollout history of a Deployment
  k rollout history deploy <deployment-name>
• Determine Deployment (owner) of a pod
  k get pods <pod-name> -o yaml | grep -A 5 owner
• Delete Deployment and all its pods
  k delete deploy <deployment-name>
• Delete Deployment only
  k delete deploy <deployment-name> --cascade=orphan