Add Storage

Core Concepts

Many applications and services need a physical volume or storage to store their data or configuration.
As you should know, we use AKS (Kubernetes) to host everything from databases to telegram bots.
In our AKS cluster we have (ATTOW) a single node (VM) Standard_B2ms which allows to attach only 4 disks, one of which is the VM's disk itself. This means that you can only attach 3 managed disks to the Cluster, resulting in limited deployable services.

To solve this problem, we added Longhorn so that we can create multiple PVC from the VM's disk (ATTOW it's a 128GB Standard SSD).

important

Longhorn is a handy tool to create multiple PVC/volumes without creating new disks, but this comes with degraded performance and stability.
If you want to deploy something critical like a production database, it's recommended to create a dedicated Managed Disk.

Add a Longhorn volume

First of all, you must login in our Longhorn dashboard and check how much space is available for scheduling a new volume.

tip

• Schedulable is space you can use to create new volumes
• Reserved is space reserved to the VM, not available to create new volumes

How much Reserved space is configured in the Node page, but at least 20-25 GB is recommended.

Once you verified you have sufficient Schedulable space available, you can create the PVC in the k8s manifest:

my-longhorn-example.yaml

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: <name>-pvc
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: longhorn-static
  resources:
    requests:
      storage: <size>
---
kind: Pod
apiVersion: v1
metadata:
  name: my-longhorn-example-pod
  namespace: <namespace>
spec:
  containers:
    - name: busybox
      image: registry.k8s.io/e2e-test-images/busybox:1.29-4
      command:
        - '/bin/sleep'
        - '10000'
      volumeMounts:
        - name: my-volume # Name of the volume defined below
          mountPath: /app/data # Where you need to mount the volume
  volumes:
    - name: my-volume # it can be whatever you want
      persistentVolumeClaim:
        claimName: <name>-pvc # the name of the PVC defined above

Parameters:

• namespace k8s namespace
• name should identify the app where the volume will be used
• size size of the volume. Check resource units. e.g. 300M, 1Gi, 200Mi