added some PVC migration notes

vlads-notes/0003-k8s-ops.md

@@ -0,0 +1,164 @@
+---
+title: Various K8s ops to remember
+tags:
+  - k8s
+  - learning-notes
+  - guides
+draft: false
+date: 2025-12-14
+---
+
+### Migrating data between PVCs
+
+Let's say I have a pod using a PVC that relies on a PV that uses NFS as a storage backend. At some point I want to make this pod use a quicker backend like Longhorn, without losing any data in the process. One option to achieve this is to us a temporary Pod to replicate the data into the new PVC. Here are the steps along with an example of migrating the storage of a Gitea Actions runner:
+
+1. create a new PV using the new storage backend + a new PVC that binds to it
+
+The storage backend of the new PVC is Longhorn:
+
+```
+# pvc.yaml
+
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+    name: gitea-run-1-pvc
+    namespace: dev-stuff
+spec:
+    storageClassName: longhorn-static
+    accessModes:
+        - ReadWriteOnce
+    resources:
+        requests:
+            storage: 5Gi
+```
+
+Apply the manifest and check that the PVC is is "bound" state:
+
+```
+kubectl apply -f pvc.yaml
+
+# OUTPUT:
+persistentvolumeclaim/gitea-run-1-pvc created
+
+kubectl get pvc -n dev-stuff
+
+# OUTPUT:
+gitea-run-1-pvc          Bound    pvc-17af2514-7307-4d74-b343-33c31607ad12   5Gi        RWO            longhorn-static   <unset>                 56s
+
+```
+
+2. scale down the Deployment to 0 replicas
+
+```
+kubectl scale deployment -n dev-stuff gitea-runner-1 --replicas=0
+
+# OUTPUT:
+deployment.apps/gitea-runner-1 scaled
+```
+
+3. create a temporary Pod that attaches both the old and the new PVC
+
+The image of choice is "busybox", but any other image that has the basic linux utilities available will do:
+
+```
+# temp.yaml
+
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  labels:
+    app: data-mover
+  name: data-mover
+  namespace: dev-stuff
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: data-mover
+  template:
+    metadata:
+      labels:
+        app: data-mover
+    spec:
+      containers:
+      - args:
+        - -c
+        - while true; do ping localhost; sleep 60;done
+        command:
+        - /bin/sh
+        image: busybox:latest
+        name: data-mover
+        volumeMounts:
+        - mountPath: /source
+          name: source
+        - mountPath: /destination
+          name: destination
+      restartPolicy: Always
+      volumes:
+      - name: source
+        persistentVolumeClaim:
+          claimName: gitea-runner-1-pvc
+      - name: destination
+        persistentVolumeClaim:
+          claimName: gitea-run-1-pvc
+```
+
+Apply the manifest and check that the pod is running:
+
+```
+kubectl get pods -n dev-stuff
+
+# OUTPUT:
+NAME                                  READY   STATUS    RESTARTS   AGE
+data-mover-5ff6cfcbfc-9cd8f           1/1     Running   0          31s
+```
+
+
+3. copy all the data across
+
+Exec into the newly created pod and copy the contents of "/source" into "/destination":
+
+```
+kubectl exec -it -n dev-stuff data-mover-5ff6cfcbfc-9cd8f -- sh
+copy -r source/* destination/*
+exit
+```
+
+4. remove the "data-mover" deployment
+
+```
+kuebctl delete -f temp.yaml
+```
+
+5. modify the Deployment to mount the new PVC
+
+```
+kubectl edit deployment -n dev-stuff gitea-runner-1
+
+# Change the line that references the PVC to use the new one:
+
+volumes:                                                                         - name: runner-data                                                                persistentVolumeClaim:                                                             claimName: gitea-run-1-pvc  # This was previously "gitea-runner-1-pvc"
+
+# Then save and close. The manifest should be applied with the new values
+
+# OUTPUT:
+deployment.apps/gitea-runner-1 edited
+```
+
+5. scale up the Deployment and check that everything works as expected
+
+```
+kubectl scale deployment -n dev-stuff gitea-runner-1 --replicas=1
+
+# OUTPUT:
+deployment.apps/gitea-runner-1 scaled
+
+kubectl get pods -n dev-stuff
+
+
+# OUTPUT:
+NAME                                  READY   STATUS    RESTARTS   AGE
+gitea-runner-1-754f74b9c4-vlqrf       1/1     Running   0          90s
+```
+