Deployments in Kubernetes
A Deployment in Kubernetes provides declarative updates for Pods and ReplicaSets. You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate. Deployments are defined using YAML (preferred) or JSON, like all Kubernetes objects.
Table of Contents
Why Use a Deployment?
Deployments are crucial when you want to ensure that a specified number of identical Pods are always up and running. They allow for easy updating of Pods without causing downtime by incrementally updating Pods instances with new ones.
Creating Deployments
You can create a Deployment by defining a .yaml or .json file and using kubectl apply -f command.
Updating Deployments
You can update a Deployment by applying a new .yaml or .json file with the updated configuration. The Deployment will ensure that the Pods transition to the new state while maintaining the desired number of Pods.
Rolling Back a Deployment
If an update to a Deployment is not stable, you can roll back to a previous state easily using the kubectl rollout undo command.
Scaling a Deployment
You can scale the number of Pods in a Deployment using the kubectl scale command or by updating the .yaml or .json file.
Cheat Sheets
| Name | Command |
|---|---|
| List all deployments | kubectl get deployments |
| List all deployments for all namespaces | kubectl get deployments -A |
| List all deployments in ps output format with more information (such as node name) | kubectl get deployments -o wide |
| Get deployment configurations as yaml | kubectl get deployment <NAME> -o yaml |
| Get deployment information | kubectl describe deployment/<NAME> |
| List a single deployment with specified NAME in ps output format | kubectl get deployment <NAME> |
| List all deployments with labels | kubectl get deployments --show-labels |
| List deployments in JSON output format, in the “v1” version of the “apps” API group | kubectl get deployments.v1.apps -o json |
| List a single deployment in JSON output format | kubectl get -o json deployment/<NAME> |
| List a deployment identified by type and name specified in “deployment.yaml” in JSON | kubectl get -f deployment.yaml -o json |
| List resources from a directory with kustomization.yaml - e.g. dir/kustomization.yaml | kubectl get -k dir/ |
| Scale a deployment | kubectl scale deployment/<NAME> --replicas=<NUMBER> |
| Rollout status of a deployment | kubectl rollout status deployment/<NAME> |
| Rollback a deployment | kubectl rollout undo deployment/<NAME> |
| List deployment information in custom columns | kubectl get deployment NAME -o custom-columns=READY:.status.readyReplicas,UPDATED:.status.updatedReplicas |
| List all replication controllers, services and deployments together in ps output format | kubectl get rc,services,deployments |
| List one or more resources by their type and names | kubectl get rc/<NAME> service/<NAME> deployment/<NAME> |