Use Azure Container Storage Preview with temp SSD

Article
06/20/2024

Azure Container Storage is a cloud-based volume management, deployment, and orchestration service built natively for containers. This article shows you how to configure Azure Container Storage to use Ephemeral Disk with temp SSD as back-end storage for your Kubernetes workloads. At the end, you'll have a pod that's using temp SSD as its storage.

What is Ephemeral Disk?

When your application needs sub-millisecond storage latency and doesn't require data durability, you can use Ephemeral Disk with Azure Container Storage to meet your performance requirements. Ephemeral means that the disks are deployed on the local virtual machine (VM) hosting the AKS cluster and not saved to an Azure storage service. Data will be lost on these disks if you stop/deallocate your VM.

There are two types of Ephemeral Disk available: NVMe and temp SSD. NVMe is designed for high-speed data transfer between storage and CPU. Choose NVMe when your application requires higher IOPS and throughput than temp SSD, or if your workload requires replication. Replication isn't currently supported for temp SSD.

Prerequisites

If you don't have an Azure subscription, create a free account before you begin.
This article requires the latest version (2.35.0 or later) of the Azure CLI. See How to install the Azure CLI. If you're using the Bash environment in Azure Cloud Shell, the latest version is already installed. If you plan to run the commands locally instead of in Azure Cloud Shell, be sure to run them with administrative privileges. For more information, see Get started with Azure Cloud Shell.
You'll need the Kubernetes command-line client, kubectl. It's already installed if you're using Azure Cloud Shell, or you can install it locally by running the az aks install-cli command.
If you haven't already installed Azure Container Storage, follow the instructions in Use Azure Container Storage with Azure Kubernetes Service.
Check if your target region is supported in Azure Container Storage regions.

Choose a VM type that supports temp SSD

Ephemeral Disk is only available in certain types of VMs. If you plan to use Ephemeral Disk with temp SSD, a Ev3 and Esv3-series VM is required.

You can run the following command to get the VM type that's used with your node pool.

az aks nodepool list --resource-group <resource group> --cluster-name <cluster name> --query "[].{PoolName:name, VmSize:vmSize}" -o table

The following is an example of output.

PoolName    VmSize
----------  ---------------
nodepool1   standard_l8s_v3

We recommend that each VM have a minimum of four virtual CPUs (vCPUs), and each node pool have at least three nodes.

Create and attach generic ephemeral volumes

Follow these steps to create and attach a generic ephemeral volume.

1. Create a storage pool

First, create a storage pool, which is a logical grouping of storage for your Kubernetes cluster, by defining it in a YAML manifest file.

If you enabled Azure Container Storage using az aks create or az aks update commands, you might already have a storage pool. Use kubectl get sp -n acstor to get the list of storage pools. If you have a storage pool already available that you want to use, you can skip this section and proceed to Display the available storage classes.

Follow these steps to create a storage pool using temp SSD.

Use your favorite text editor to create a YAML manifest file such as code acstor-storagepool.yaml.

Paste in the following code and save the file. The storage pool name value can be whatever you want.

apiVersion: containerstorage.azure.com/v1
kind: StoragePool
metadata:
  name: ephemeraldisk
  namespace: acstor
spec:
  poolType:
    ephemeralDisk:
      diskType: temp

Apply the YAML manifest file to create the storage pool.
```
kubectl apply -f acstor-storagepool.yaml 
```
When storage pool creation is complete, you'll see a message like:
```
storagepool.containerstorage.azure.com/ephemeraldisk created
```
You can also run this command to check the status of the storage pool. Replace <storage-pool-name> with your storage pool name value. For this example, the value would be ephemeraldisk.
```
kubectl describe sp <storage-pool-name> -n acstor
```

When the storage pool is created, Azure Container Storage will create a storage class on your behalf, using the naming convention acstor-<storage-pool-name>.

2. Display the available storage classes

When the storage pool is ready to use, you must select a storage class to define how storage is dynamically created when creating persistent volume claims and deploying persistent volumes.

Run kubectl get sc to display the available storage classes. You should see a storage class called acstor-<storage-pool-name>.

$ kubectl get sc | grep "^acstor-"
acstor-azuredisk-internal   disk.csi.azure.com               Retain          WaitForFirstConsumer   true                   65m
acstor-ephemeraldisk        containerstorage.csi.azure.com   Delete          WaitForFirstConsumer   true                   2m27s

Important

Don't use the storage class that's marked internal. It's an internal storage class that's needed for Azure Container Storage to work.

3. Deploy a pod with a generic ephemeral volume

Create a pod using Fio (Flexible I/O Tester) for benchmarking and workload simulation, that uses a generic ephemeral volume.

Use your favorite text editor to create a YAML manifest file such as code acstor-pod.yaml.

Paste in the following code and save the file.

kind: Pod
apiVersion: v1
metadata:
  name: fiopod
spec:
  nodeSelector:
    acstor.azure.com/io-engine: acstor
  containers:
    - name: fio
      image: nixery.dev/shell/fio
      args:
        - sleep
        - "1000000"
      volumeMounts:
        - mountPath: "/volume"
          name: ephemeralvolume
  volumes:
    - name: ephemeralvolume
      ephemeral:
        volumeClaimTemplate:
          metadata:
            labels:
              type: my-ephemeral-volume
          spec:
            accessModes: [ "ReadWriteOnce" ]
            storageClassName: "acstor-ephemeraldisk-nvme" # replace with the name of your storage class if different
            resources:
              requests:
                storage: 1Gi

Apply the YAML manifest file to deploy the pod.
```
kubectl apply -f acstor-pod.yaml
```
You should see output similar to the following:
```
pod/fiopod created
```
Check that the pod is running and that the ephemeral volume claim has been bound successfully to the pod:
```
kubectl describe pod fiopod
kubectl describe pvc fiopod-ephemeralvolume
```

Check fio testing to see its current status:

kubectl exec -it fiopod -- fio --name=benchtest --size=800m --filename=/volume/test --direct=1 --rw=randrw --ioengine=libaio --bs=4k --iodepth=16 --numjobs=8 --time_based --runtime=60

You've now deployed a pod that's using temp SSD as its storage, and you can use it for your Kubernetes workloads.

Manage storage pools

Now that you've created your storage pool, you can expand or delete it as needed.

Expand a storage pool

You can expand storage pools backed by temp SSD to scale up quickly and without downtime. Shrinking storage pools isn't currently supported.

Because a storage pool backed by Ephemeral Disk uses local storage resources on the AKS cluster nodes (VMs), expanding the storage pool requires adding another node to the cluster. Follow these instructions to expand the storage pool.

Run the following command to add a node to the AKS cluster. Replace <cluster-name>, <nodepool name>, and <resource-group-name> with your own values. To get the name of your node pool, run kubectl get nodes.
```
az aks nodepool add --cluster-name <cluster name> --name <nodepool name> --resource-group <resource group> --node-vm-size Standard_L8s_v3 --node-count 1 --labels acstor.azure.com/io-engine=acstor
```
Run kubectl get nodes and you'll see that a node has been added to the cluster.
Run kubectl get sp -A and you should see that the capacity of the storage pool has increased.

Delete a storage pool

If you want to delete a storage pool, run the following command. Replace <storage-pool-name> with the storage pool name.

kubectl delete sp -n acstor <storage-pool-name>

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