A deployment is used to manage the pods that are created to run an application. The deployment ensures that the desired number of pod replicas are running and can handle updates to the application by rolling out new versions of the pods. The deployment creates and manages a replica set, which in turn manages the pods.
Container] Pod2[Pod 2
Container] Pod3[Pod 3
Container] end end Deployment -->|Creates/Manages| Replica_Set Replica_Set -->|Manages| Pod1 Replica_Set -->|Manages| Pod2 Replica_Set -->|Manages| Pod3 style Deployment fill:#90CAF9 style Replica_Set fill:#FFE082 style Pods fill:#FFCCBC
It is also noteworthy that a route provides a URL that can be used to access the application from outside the OpenShift cluster. For example, if the route is configured to use the hostname myapp.mydomain.com, then users can access the application by navigating to http://myapp.mydomain.com. The route will forward the request to the service, which will then forward the request to one of the pods that are running the application.
Container] Pod2[Pod 2
Container] Pod3[Pod 3
Container] end SVC[Service] Route[Route] end USER[External User] --> Route --> SVC SVC --> Pod1 SVC --> Pod2 SVC --> Pod3 style SVC fill:#A5D6A7 style Pods fill:#FFCCBC style USER fill:#CE93D8
If you are not familiar with the oc command, refer to OpenShift - Getting Started with the oc command.
The oc get deployments command can be used to list the deployments in the currently selected project.
~]# oc get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
my-app 1/1 1 1 8d
Or, If the --as-deployment-config flag is used, the application will be created as a deployment config. In this scenario, a replication controller will be used to create the pods and the oc get deploymentconfigs (or oc get dc) command would be used to list the deployments.
~]$ oc get deploymentconfigs
NAME REVISION DESIRED CURRENT TRIGGERED BY
my-app 1 1 1 config,image(my-app:latest)
If you have numerous deployments, the -l option can be used to only return the deployments that match the app name.
oc get deployments -l app=my-app
If READY is 0/0 or AVAILABLE is 0, you may need to restart the deployment.
NAME READY UP-TO-DATE AVAILABLE AGE
my-app 0/0 0 0 8d
The --output wide option can be used to display more information about the deployment. The oc config view or oc get apiserver commands can be used to display the API Server URL (api.openshift.example.com in this example).
~]$ oc get deployments --output wide
NAME READY UP-TO-DATE AVAILABLE AGE CONTAINERS IMAGES SELECTOR
my-app 1/1 1 1 8d my-container api.openshift.example.com/myapp app=app001
The --output yaml or --output json options can be used to display even more information about the deployment.
oc get deployment my-app --output yaml
Something like this should be returned.
apiVersion: v1
kind: Deployment
metadata:
annotations:
deployment.kubernetes.io/revision: "1"
openshift.io/generated-by: OpenShiftNewApp
creationTimestamp: "2021-03-23T22:06:06Z"
generation: 1
name: my-app
namespace: default
resourceVersion: "450841867"
uid: fff40384-0b81-4016-8ff7-6a755c3d1792
spec:
replicas: 1
spec:
- image: api.openshift.example.com/myapp
imagePullPolicy: IfNotPresent
name: my-app
ports:
- containerPort: 8080
protocol: TCP
- containerPort: 8443
protocol: TCP
resources: {}
terminationMessagePath: /dev/termination-log
terminationMessagePolicy: File
dnsPolicy: ClusterFirst
restartPolicy: Always
schedulerName: default-scheduler
securityContext: {}
terminationGracePeriodSeconds: 30
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