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Deployments

Updated Apr 07, 2022 ·

Overview​

A Deployment simplifies Pod management in Kubernetes, ensuring they meet the desired state. It handles scaling, updates, and rollbacks.

  • Manages Pods' desired state
  • Scales by creating replicas
  • Adjusts state during changes
  • Supports rolling updates with configurable behaviors

Deployment Manifest​

The Deployment manifest defines key components to manage Pod creation and updates:

  • replicas: Specifies how many Pod replicas should be created
  • selector: Uses label selectors to track Pods, ensuring the correct Pods are managed by the Deployment
  • template: Defines the desired behavior of the Pods (similar to a Pod manifest)

Example Deployment Manifest:

data-tier.yml
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: data-tier
  namespace: deployment
  labels:
    app: microservices
    tier: data
spec:
  replicas: 1
  selector:
    matchLabels:
      tier: data
  template:
    metadata:
      labels:
        app: microservices
        tier: data
    spec:
      containers:
      - name: redis
        image: redis:latest
        imagePullPolicy: IfNotPresent
        ports:
          - containerPort: 6379

To create the Deployment:

kubectl apply -f data-tier.yml

To view Deployment details, use the describe command:

kubectl describe deployments data-tier

Example output:

Name:                   data-tier
Namespace:              deployment
CreationTimestamp:      Thu, 5 Jul 2022 16:18:28 +0000
Labels:                 app=microservices
                        tier=data
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               tier=data
Replicas:               1 desired | 1 updated | 1 total | 1 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
    Labels:  app=microservices
            tier=data
    Containers:
    redis:
    Image:        redis:latest
    Port:         6379/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
    Volumes:        <none>
Conditions:
    Type           Status  Reason
    ----           ------  ------
    Available      True    MinimumReplicasAvailable
    Progressing    True    NewReplicaSetAvailable
OldReplicaSets:  <none>
NewReplicaSet:   data-tier-d45bbd7dc (1/1 replicas created)
Events:
    Type    Reason             Age   From                   Message
    ----    ------             ----  ----                   -------
    Normal  ScalingReplicaSet  11s   deployment-controller  Scaled up replica set data-tier-d45bbd7dc to 1

Key highlights from the output:

  • StrategyType: Defines the update method

    • RollingUpdate: Ensures incremental updates to Pods

  • RollingUpdateStrategy: Controls the rolling update process

    • max unavailable: Limits unavailable Pods during updates
    • max surge: Limits Pods exceeding the desired count during updates

For more information, please see Rollouts and Rollbacks.