Use storage mounts in Azure Container Apps

Article
10/14/2022
6 minutes to read

A container app has access to different types of storage. A single app can take advantage of more than one type of storage if necessary.

Storage type	Description	Usage examples
Container file system	Temporary storage scoped to the local container	Writing a local app cache.
Temporary storage	Temporary storage scoped to an individual replica	Sharing files between containers in a replica. For instance, the main app container can write log files that are processed by a sidecar container.
Azure Files	Permanent storage	Writing files to a file share to make data accessible by other systems.

Note

The volume mounting features in Azure Container Apps are in preview.

Container file system

A container can write to its own file system.

Container file system storage has the following characteristics:

The storage is temporary and disappears when the container is shut down or restarted.
Files written to this storage are only visible to processes running in the current container.
There are no capacity guarantees. The available storage depends on the amount of disk space available in the container.

Temporary storage

You can mount an ephemeral volume that is equivalent to emptyDir in Kubernetes. Temporary storage is scoped to a single replica.

Temporary storage has the following characteristics:

Files are persisted for the lifetime of the replica.
- If a container in a replica restarts, the files in the volume remain.
Any containers in the replica can mount the same volume.
A container can mount multiple temporary volumes.
There are no capacity guarantees. The available storage depends on the amount of disk space available in the replica.

To configure temporary storage, first define an EmptyDir volume in the revision. Then define a volume mount in one or more containers in the revision.

Prerequisites

Requirement	Instructions
Azure account	If you don't have one, create an account for free.
Azure Container Apps environment	Create a container apps environment.

Configuration

When using temporary storage, you must use the Azure CLI with a YAML definition to create or update your container app.

To update an existing container app to use temporary storage, export your app's specification to a YAML file named app.yaml.
```
az containerapp show -n <APP_NAME> -g <RESOURCE_GROUP_NAME> -o yaml > app.yaml
```
Make the following changes to your container app specification.
- Add a volumes array to the template section of your container app definition and define a volume.
  - The name is an identifier for the volume.
  - Use EmptyDir as the storageType.
- For each container in the template that you want to mount temporary storage, add a volumeMounts array to the container definition and define a volume mount.
  - The volumeName is the name defined in the volumes array.
  - The mountPath is the path in the container to mount the volume.
```
properties:
  managedEnvironmentId: /subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCE_GROUP_NAME>/providers/Microsoft.App/managedEnvironments/<ENVIRONMENT_NAME>
  configuration:
    activeRevisionsMode: Single
  template:
    containers:
    - image: <IMAGE_NAME>
      name: my-container
      volumeMounts:
      - mountPath: /myempty
        volumeName: myempty
    volumes:
    - name: myempty
      storageType: EmptyDir
```

Update your container app using the YAML file.

az containerapp update --name <APP_NAME> --resource-group <RESOURCE_GROUP_NAME> \
    --yaml app.yaml

To create a temporary volume and mount it in a container, make the following changes to the container apps resource in an ARM template:

Add a volumes array to the template section of your container app definition and define a volume.
- The name is an identifier for the volume.
- Use EmptyDir as the storageType.
For each container in the template that you want to mount temporary storage, add a volumeMounts array to the container definition and define a volume mount.
- The volumeName is the name defined in the volumes array.
- The mountPath is the path in the container to mount the volume.

Example ARM template snippet:

{
  "apiVersion": "2022-03-01",
  "type": "Microsoft.App/containerApps",
  "name": "[parameters('containerappName')]",
  "location": "[parameters('location')]",
  "properties": {

    ...

    "template": {
      "revisionSuffix": "myrevision",
      "containers": [
        {
          "name": "main",
          "image": "[parameters('container_image')]",
          "resources": {
            "cpu": 0.5,
            "memory": "1Gi"
          },
          "volumeMounts": [
            {
              "mountPath": "/myempty",
              "volumeName": "myempty"
            }
          ]
        }
      ],
      "scale": {
        "minReplicas": 1,
        "maxReplicas": 3
      },
      "volumes": [
        {
          "name": "myempty",
          "storageType": "EmptyDir"
        }
      ]
    }
  }
}

See the ARM template API specification for a full example.

Azure Files

You can mount a file share from Azure Files as a volume inside a container.

For a step-by-step tutorial, refer to Create an Azure Files storage mount in Azure Container Apps.

Azure Files storage has the following characteristics:

Files written under the mount location are persisted to the file share.
Files in the share are available via the mount location.
Multiple containers can mount the same file share, including ones that are in another replica, revision, or container app.
All containers that mount the share can access files written by any other container or method.
More than one Azure Files volume can be mounted in a single container.

To enable Azure Files storage in your container, you need to set up your container in the following ways:

Create a storage definition of type AzureFile in the Container Apps environment.
Define a storage volume in a revision.
Define a volume mount in one or more containers in the revision.

Prerequisites

Requirement	Instructions
Azure account	If you don't have one, create an account for free.
Azure Storage account	Create a storage account.
Azure Container Apps environment	Create a container apps environment.

Configuration

When using Azure Files, you must use the Azure CLI with a YAML definition to create or update your container app.

Add a storage definition of type AzureFile to your Container Apps environment.
```
az containerapp env storage set --name my-env --resource-group my-group \
    --storage-name mystorage \
    --azure-file-account-name <STORAGE_ACCOUNT_NAME> \
    --azure-file-account-key <STORAGE_ACCOUNT_KEY> \
    --azure-file-share-name <STORAGE_SHARE_NAME> \
    --access-mode ReadWrite
```
Replace <STORAGE_ACCOUNT_NAME> and <STORAGE_ACCOUNT_KEY> with the name and key of your storage account. Replace <STORAGE_SHARE_NAME> with the name of the file share in the storage account.

Valid values for --access-mode are ReadWrite and ReadOnly.
To update an existing container app to mount a file share, export your app's specification to a YAML file named app.yaml.
```
az containerapp show -n <APP_NAME> -g <RESOURCE_GROUP_NAME> -o yaml > app.yaml
```
Make the following changes to your container app specification.
- Add a volumes array to the template section of your container app definition and define a volume.
  - The name is an identifier for the volume.
  - For storageType, use AzureFile.
  - For storageName, use the name of the storage you defined in the environment.
- For each container in the template that you want to mount Azure Files storage, add a volumeMounts array to the container definition and define a volume mount.
  - The volumeName is the name defined in the volumes array.
  - The mountPath is the path in the container to mount the volume.
```
properties:
  managedEnvironmentId: /subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCE_GROUP_NAME>/providers/Microsoft.App/managedEnvironments/<ENVIRONMENT_NAME>
  configuration:
  template:
    containers:
    - image: <IMAGE_NAME>
      name: my-container
      volumeMounts:
      - volumeName: azure-files-volume
        mountPath: /my-files
    volumes:
    - name: azure-files-volume
      storageType: AzureFile
      storageName: mystorage
```

Update your container app using the YAML file.

az containerapp update --name <APP_NAME> --resource-group <RESOURCE_GROUP_NAME> \
    --yaml app.yaml

The following ARM template snippets demonstrate how to add an Azure Files share to a Container Apps environment and use it in a container app.

Add a storages child resource to the Container Apps environment.

{
  "type": "Microsoft.App/managedEnvironments",
  "apiVersion": "2022-03-01",
  "name": "[parameters('environment_name')]",
  "location": "[parameters('location')]",
  "properties": {
    "daprAIInstrumentationKey": "[parameters('dapr_ai_instrumentation_key')]",
    "appLogsConfiguration": {
      "destination": "log-analytics",
      "logAnalyticsConfiguration": {
        "customerId": "[parameters('log_analytics_customer_id')]",
        "sharedKey": "[parameters('log_analytics_shared_key')]"
      }
    }
  },
  "resources": [
    {
      "type": "storages",
      "name": "myazurefiles",
      "apiVersion": "2022-03-01",
      "dependsOn": [
        "[resourceId('Microsoft.App/managedEnvironments', parameters('environment_name'))]"
      ],
      "properties": {
        "azureFile": {
          "accountName": "[parameters('storage_account_name')]",
          "accountKey": "[parameters('storage_account_key')]",
          "shareName": "[parameters('storage_share_name')]",
          "accessMode": "ReadWrite"
        }
      }
    }
  ]
}

Update the container app resource to add a volume and volume mount.

{
  "apiVersion": "2022-03-01",
  "type": "Microsoft.App/containerApps",
  "name": "[parameters('containerappName')]",
  "location": "[parameters('location')]",
  "properties": {

    ...

    "template": {
      "revisionSuffix": "myrevision",
      "containers": [
        {
          "name": "main",
          "image": "[parameters('container_image')]",
          "resources": {
            "cpu": 0.5,
            "memory": "1Gi"
          },
          "volumeMounts": [
            {
              "mountPath": "/myfiles",
              "volumeName": "azure-files-volume"
            }
          ]
        }
      ],
      "scale": {
        "minReplicas": 1,
        "maxReplicas": 3
      },
      "volumes": [
        {
          "name": "azure-files-volume",
          "storageType": "AzureFile",
          "storageName": "myazurefiles"
        }
      ]
    }
  }
}

Add a volumes array to the template section of your container app definition and define a volume.
- The name is an identifier for the volume.
- For storageType, use AzureFile.
- For storageName, use the name of the storage you defined in the environment.
For each container in the template that you want to mount Azure Files storage, add a volumeMounts array to the container definition and define a volume mount.
- The volumeName is the name defined in the volumes array.
- The mountPath is the path in the container to mount the volume.

See the ARM template API specification for a full example.

Use storage mounts in Azure Container Apps

Container file system

Temporary storage

Prerequisites

Configuration

Azure Files

Prerequisites

Configuration

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Additional resources

Additional resources