A Deployment provides declarative updates for Pods and ReplicaSets.
- A deployment defines the desired state for replica pods.
- The cluster constantly maintains the desired state by creating, removing, and modifying replica pods.
Creating Deployments
Deployment definition file need 3 sections:
- spec.replicas: The number of replica pods
- spec.template: A template definition which defines a pod
- spec.template.metadata
- spec.template.spec
- spec.selector: the deployment will manage all pods whose labels match this selector
(Example) A simple deployment of 2 nginx pods
- Create a YAML file
apiVersion: apps/v1
kind: Deployment
metadata:
name: my-nginx
spec:
replicas: 2
selector:
matchLabels:
app: my-nginx
template:
metadata:
labels:
app: my-nginx
spec:
containers:
- name: my-nginx
image: nginx:1.19.1
ports:
- containerPort: 80
- Create/Apply
kubectl create -f <yaml-file>
# Use --save-config
# when you want to use 'kubectl apply' in the future
kubectl create -f <yaml-file> --save-config
kubectl apply -f <yaml-file>
Checking Deployments
kubectl get deployments
kubectl get pods –l app=my-nginx
kubectl get deployment <deployment-name>
kubectl describe deployment <deployment-name>
kubectl delete deployment <deployment-name>
Editing Deployments
With deployments, you can easily edit any field/property of the pod template such as the number of replicas.
kubectl edit deployment <deployment-name>
# modify spec.replicas
# check the pods
kubectl get pods
Checking replica sets
kubectl get replicasets
kubectl get rs
# check 'NewReplicaSet' property
kubectl describe deploy <deploy-name>
kubectl describe rs <replicaset-name>
Scaling
kubectl scale deploy <deploy-name> --replicas=5
kubectl describe deploy <deploy-name>
kubectl get pods
Deployment Strategies
- Rolling Update
- (default) gradually updates replicas so that there is no downtime
- maxSurge:
- how many pods to add at a time
- number or percentage (25% default)
- maxUnavailable
- how many pods can be unavailable during the rolling update
- number or percentage (25% default)
- Recreate
- All existing Pods are killed before new ones are created.
- All applications are entirely updated but there might be some downtime.
spec:
replicas: 3
strategy:
type: RollingUpdate
rollingUpdate:
maxSurge: 2
maxUnavailable: 0
spec:
replicas: 3
strategy:
type: Recreate
Performing an update
# Update the deployment yaml file with a new image
kubectl apply –f my-deployment.yaml
# Or Peform a rolling update
kubectl set image deployment/<deployment-name> \
<container-name>=nginx:1.19.7 --record
Checking the rollout status/history
kubectl rollout status deploy/<deploy-name>
kubectl rollout status deploy/<deploy-name> --revision=2
kubectl rollout history deploy/<deploy-name>
kubectl rollout history deploy/<deploy-name> --revision=2
Performing the rollback
kubectl rollout undo deploy/<deploy-name>
kubectl rollout undo deploy/<deploy-name> --to-revision=2
Scriptorium 