Kubernetes -- Helm -- Mysql Chart loses stored data after stopping pod - mysql

Question

Using https://github.com/helm/charts/tree/master/stable/mysql (all the code is here), it is cool being able to run mysql as part of my local kubernetes cluster (using docker kubernetes).
The problem though is that once I stop running the pod, and then run the pod again, all the data that was stored is now gone.
My question is how do I keep the data that was added to the mysql pod? I have read about persistent volumes, and the mysql helm example from github is showing that it is using PersistentVolumeClaim. I have also enabled persistence on the values.yaml file, but I cannot seem to have the same data that was saved in the database.
My docker kubernetes version is currently 1.14.6.

Answer 1

Please verify your msql POD You should notice volumes and volumesMount options:
volumeMounts:
- mountPath: /var/lib/mysql
name: data
.
.
.
volumes:
- name: data
persistentVolumeClaim:
claimName: msq-mysql
In additions please verify your PersistentVolume and PersistentVolumeClaim, storageClass:
kubectl get pv,pvc,pods,sc:
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
persistentvolume/pvc-2c6aa172-effd-11e9-beeb-42010a840083 8Gi RWO Delete Bound default/msq-mysql standard 24m
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
persistentvolumeclaim/msq-mysql Bound pvc-2c6aa172-effd-11e9-beeb-42010a840083 8Gi RWO standard 24m
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
pod/msq-mysql-b5c48c888-pz6p2 1/1 Running 0 4m28s 10.0.0.8 gke-te-1-default-pool-36546f4e-5rgw <none> <none>
Please run kubectl describe persistentvolumeclaim/msq-mysql (in your example you should change the pvc name)
You can notice that pvc was provisioned successfully using gce-pd and mounted by msq-mysql POD.
Normal ProvisioningSucceeded 26m persistentvolume-controller Successfully provisioned volume pvc-2c6aa172-effd-11e9-beeb-42010a840083 using kubernetes.io/gce-pd
Mounted By: msq-mysql-b5c48c888-pz6p2
I have created table with on row, deleted the pod and verified after that (as expected everything is alright):
mysql> SELECT * FROM t;
+------+
| c |
+------+
| ala |
+------+
1 row in set (0.00 sec)
Why: all the data that was stored is now gone.
As per helm chart docs:
The MySQL image stores the MySQL data and configurations at the /var/lib/mysql path of the container.
By default a PersistentVolumeClaim is created and mounted into that directory. In order to disable this functionality you can change the values.yaml to disable persistence and use an emptyDir instead.
Mostly there is problem with pv,pvc binding. It can be also problem with user defined or non default storageClass.
So please verify pv,pvc as stated above.
Take a look at StorageClass
A claim can request a particular class by specifying the name of a StorageClass using the attribute storageClassName. Only PVs of the requested class, ones with the same storageClassName as the PVC, can be bound to the PVC.
PVCs don’t necessarily have to request a class. A PVC with its storageClassName set equal to "" is always interpreted to be requesting a PV with no class, so it can only be bound to PVs with no class (no annotation or one set equal to ""). A PVC with no storageClassName is not quite the same and is treated differently by the cluster, depending on whether the DefaultStorageClass admission plugin is turned on.