Background
If you follow my Blog or read my last post on delivering Oracle 18c Express Edition Database (XE) in Kubernetes you may already have Oracle 18XE database up and running on Kubernetes cluster using persistent storage. If not, you may want to read this.
In this Blog I am going to show how we can relocate our Oracle 18XE database to a different node of a Kubernetes cluster simply using Kubernetes command line tool kubectl.
My Oracle 18xe database is using persistent storage delivered from a Pure FlashArray in my lab with the Pure Storage Orchestrator (PSO) presenting volumes to my Kubernetes node via iSCSI.
If you want to read-up on how I did that, check you my previous blog post How to run Oracle on Kubernetes with Persistent Storage.
Getting Started
Let’s start by listing the Kubernetes names and statuses of nodes with kubectl get nodes
$ kubectl get nodes NAME STATUS ROLES AGE VERSION z-re-uk8s01 Ready <none> 10d v1.18.2-41+b5cdb79a4060a3 z-re-uk8s02 Ready <none> 10d v1.18.2-41+b5cdb79a4060a3 z-re-uk8s03 Ready <none> 10d v1.18.2-41+b5cdb79a4060a3 z-re-uk8s04 Ready <none> 10d v1.18.2-41+b5cdb79a4060a3
We can see our running Kubernetes pods with kubectl get pods -o wide -n <namespace>. The -o wide option is required to show the node.
$ kubectl get pods -o wide-n oracle-namespace NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE oracle18xe-698648f6df-49ttr 1/1 Running 0 6m39s 10.1.68.48 z-re-uk8s03 <none>
Ok, lets make the node running our pod un-schedulable using kubectl cordon <node name>
$ kubectl cordon z-re-uk8s03
node/z-re-uk8s03 cordoned
If we check the status of the pods in the cluster we can see the status has changed to SchedulingDisabled.
$ kubectl get nodes
NAME STATUS ROLES AGE VERSION
z-re-uk8s01 Ready <none> 10d v1.18.2-41+b5cdb79a4060a3
z-re-uk8s02 Ready <none> 10d v1.18.2-41+b5cdb79a4060a3
z-re-uk8s03 Ready,SchedulingDisabled <none> 10d v1.18.2-41+b5cdb79a4060a3
z-re-uk8s04 Ready <none> 10d v1.18.2-41+b5cdb79a4060a3
We can also see our pod is still running, but we know the node will no longer schedule any new pods.
$ kubectl get pods -o wide-n oracle-namespace NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE oracle18xe-698648f6df-49ttr 1/1 Running 0 6m39s 10.1.68.48 z-re-uk8s03 <none>
If we delete the pod, and we should see the pod restarted on different node.
$ kubectl delete pod/oracle18xe-698648f6df-49ttr -n oracle-namespace
pod "oracle18xe-698648f6df-49ttr" deleted
Let’s find out where our pod has relocated to with kubectl get pods
$ kubectl get pods -n oracle-namespace -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE
oracle18xe-698648f6df-7hdnw 1/1 Running 0 2m20s 10.1.73.154 z-re-uk8s01 <none>
Before we move on, we can make the node available again with uncordon
$ kubectl uncordon z-re-uk8s03
node/z-re-uk8s03 uncordoned
Oracle Database 18xe
From the above, we can see my Oracle 18xe pod has moved from z-re-uks03 to z-re-uks01
If we connect to our container we can see our PSO persistent volume mounted.
$ kubectl exec -it oracle18xe-698648f6df-7hdnw /bin/bash -n oracle-namespace
And from my laptop I can use sqlplus to connect to the database now running on z-re-uk8s01.
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