Storage considerations for Azure Kubernetes Service (AKS)

To run specific application workloads, your organization or enterprise needs to design suitable Azure Kubernetes Service (AKS) platform-level capabilities. These workloads likely have different storage requirements. When choosing the right storage solution for your application, you have multiple considerations, including performance, availability, recoverability, security, and cost. The goal of this article is to guide you to choose the right option or combination of options for your workload.

Kubernetes can run both stateless and stateful workloads. Stateful workloads often require a storage solution for storing state. AKS supports multiple, integrated options for native storage, which include managed databases, disks (or blocks), and files and blob (or object) storage. Each of these options offers different SKUs, sizes, and performance characteristics. Selecting the right option requires careful consideration.

This article describes the factors and options that you need to consider in Select the right storage service and Design considerations. It provides specific recommendations in Design recommendations.

Select the right storage service

Choosing the right SKUs and sizes for your initial deployments requires some evaluations and, potentially, a proof-of-concept or test environment. Following are the high-level guidelines to help you get started with storage for AKS:

  • Structured data. For structured data that your application can store in a managed database that is available on the platform (for example, Azure SQL), we recommend using a managed database.

  • Unstructured data. For unstructured data—such as photos, videos, and text documents—use blob storage. Your application can do this by using blobs that are mounted as files via Network File System (NFS) or accessed as a virtual file system by using BlobFuse. Alternatively, your application can read from and write to blob storage directly.

  • Shared application data. For shared application data that requires high performance, use either Azure NetApp Files or the premium tier of Azure Files. For shared configuration data that requires only limited performance, use the standard tier of Azure Files.

  • Bandwidth for application & storage requests. Ensure that your nodes have sufficient network bandwidth to handle both application requests and storage requests. Storage traffic goes over the network stack, whether the protocol for transfers is Server Message Block (SMB) or NFS.

  • Low latency, high IOPS. Use disks for storage if your application needs consistently low latency for messaging applications and high I/O operations per second (IOPS) and high throughput to run your own databases on Kubernetes. For the best performance, consider using Azure Premium SSD, Azure Premium SSD v2, or Azure Ultra Disk Storage.

Design considerations

The following considerations are for designing storage for AKS. Consider where storage is required in your AKS environment, and determine the best solution for each requirement.

Operating system (OS) disks

For operating system (OS) disks, consider the following factors:

  • Ephemeral disks for OS. Each virtual machine (VM) in Azure requires a disk for its OS. Because Kubernetes nodes are ephemeral, AKS defaults to using ephemeral OS disks on supported VM sizes. For more information about ephemeral OS disks, see Ephemeral OS.

  • Managed disks for OS. If your workload requires them, you can instead use regular managed disks for the nodes in your AKS cluster. Doing so supports workloads that require persistent data on the OS drive. For more information about options for persistent storage, see Storage options for applications in Azure Kubernetes Service (AKS).

  • Sizing managed disks. If you select a managed disk as the OS disk, ensure that it's sized appropriately to support the requirements of the OS, the Kubernetes system, and your workload. For more information about options and differences, see Azure managed disk types.

Application data

Some workloads need a consistent data store for storage of application data. If your application requires a database, consider exploring the managed databases in Azure, which include the following options:

Storage solutions in AKS

If a managed database doesn't meet the needs of your application, consider using another storage option that's available to AKS to store consistent data. Options include disk-based solutions, ephemeral disks, files-based solutions, blob storage, and other options that aren't covered in this article.

Disk-based solutions

Disks, or block storage, are ideal for storing data directly on a raw, block-based device. Disk-based storage is ideal for storing data for databases that your Kubernetes cluster hosts. In Azure, managed disks are the solution to get block-based storage.

  • Static or dynamically created disk storage. Consider whether you want to use a static disk that's created outside of AKS, or if you want AKS to dynamically create the disk storage as a pod or pods require it. Storage that is created dynamically can also be deleted dynamically. For more information, see:

  • Redundancy and performance. Consider the storage redundancy and performance that your workload requires. For more information, see:

  • Shared disk. Consider whether you need a shared disk. For more information about options, see Share an Azure managed disk.

  • Size of node for disks and throughput. Consider the size of your Kubernetes node. It must be large enough to support both the number of disks and the aggregate throughput requirements. For information about sizes and characteristics, see Sizes for virtual machines in Azure.

  • Disk size and required performance. Consider whether your managed disk is sized appropriately for your workload's performance requirements. Performance increases as the disk size increases for Standard HDD, Standard SSD, and Premium SSD v1. For more information about managed disks, see Azure managed disk types.

Ephemeral disks solutions

Consider whether your application requires non-persistent, temporary storage or where you want to use the high-performance drives in the storage-optimized VMs. To connect to an ephemeral volume, you can use either the emptyDir option in Kubernetes or the driver for a CSI ephemeral local volume. We recommend emptyDir for ephemeral data, such as scratch space. For storage on the storage-optimized VM series, we recommend using CSI with an ephemeral local volume. For more information about CSI drivers, see Container Storage Interface (CSI) drivers on Azure Kubernetes Service (AKS).

Files-based solutions

Consider whether your pods need to share a file system. A shared file system is ideal for application and configuration data that is read and shared by multiple pods in your Kubernetes cluster. File storage exposes a shared file system via either NFS or SMB/Common Internet File System (CIFS). Azure has two solutions for file-based storage: Azure Files and Azure NetApp Files.

Azure Files

For Azure Files, consider the following options:

  • Static or dynamically created file share. Consider whether you want to use a static file share that's created outside of AKS, or if you want AKS to create the file share dynamically on your behalf. For more information, see:

  • Standard or premium performance. Evaluate if standard performance is sufficient or if you need premium performance from Azure Files.

  • SMB/CIFS or NFS. For access to Azure Files, evaluate whether your workload should use the API for the default protocol, SMB/CIFS, or if your workload requires NFS support.

  • Network model for access. Consider the network model that you want to use to access Azure Files: access via direct public IP address, a service endpoint, or a private link.

Azure NetApp Files

For Azure NetApp Files, consider the following options:

Blob storage

Consider the amount of unstructured data that your application needs to store. Azure Blob storage is accessible via an HTTP API or through the SDKs. Mounting blob storage as a file system into a container or pod is ideal for application workloads that have massive amounts of unstructured data, such as log files, images, documents, streaming media, and disaster-recovery data.

  • Data redundancy. Consider which data redundancy suits your application. For more information, see Azure Storage redundancy. Data redundancy is selected at the level of the storage account.

  • Performance tier. Consider which performance tier of blob storage your application requires. For more information, see Hot, cool, and archive access tiers for blob data.

  • Authentication method for access. Consider which authentication method that your application should use for access to blob storage: storage key, SAS, or Azure Active Directory (Azure AD). For more information, see Authorize access to data in Azure Storage.

  • API to abstract blob storage. Consider which API to use. Typically, applications that access blob storage use the API in the application through one of the SDKs, which abstracts the interaction with blob storage from the Kubernetes cluster. For more information about libraries for various programming languages, see Introduction to Azure Blob storage.

  • Static or dynamically created blob storage. Consider whether you want to use a static blob storage container that's created outside of AKS or if you want AKS to create the blob storage container dynamically on your behalf. For more information, see:

  • Driver for accessing storage. Consider how your application should access blob storage. To access it as a file system, you can use the blob CSI driver in Kubernetes. This driver allows access to blob storage through either the NFSv3 protocol or through a fuse driver.

Other storage solutions

Consider other types of storage if your application requires something that's not described in this article. There are multiple specialized storage solutions in Azure that can integrate with Kubernetes. This article doesn't cover those, but the following list identifies possible solutions:

  • Azure HPC cache. HPC Cache speeds access to your data for high-performance computing (HPC) tasks. By caching files in Azure, Azure HPC Cache brings the scalability of cloud computing to your existing workflow. For more information, see Integrate Azure HPC Cache with Azure Kubernetes Service.

  • Azure Data Lake Storage Gen2. Data Lake Storage Gen2 is a special type of blob storage that's optimized for big data workloads like Hadoop and Spark. For more information, see Introduction to Azure Data Lake Storage Gen2.

Design recommendations

This section provides recommendations that are based on what has proven to be effective for Azure customers.

  • Use Azure Private Link. For security, we recommend using Azure Private Link for all storage solutions that support it. Azure Private Link enables access to Azure Services, such as Azure Storage and SQL Database, and Azure-hosted services over a private endpoint in your virtual network. For more information, see What is Azure Private Link?

  • Use ephemeral disks for OS. For OS disks, we recommend using ephemeral disks. To benefit from this feature, select a VM size that has an adequately sized temporary disk. For more information, see Ephemeral OS disks for Azure VMs.

  • Use managed databases. For application data, we recommend using managed databases. For a list of database options, see Types of Databases on Azure.

The following sections describe more recommendations for Azure disks, Azure Files, and blob storage.

Azure disks

For Azure disks, we recommend the following design options:

  • Use Premium or Ultra disks. In most cases, we recommend Premium or Ultra disks to ensure adequate performance. For more information, see Azure Disk Storage.

  • Size the node for disks and throughput. We recommend ensuring that the size of your Kubernetes node is large enough to support the number of disks and the amount of aggregate throughput. For information about sizes and characteristics, see Sizes for virtual machines in Azure.

  • Create snapshots of persistent volumes. We recommend taking snapshots of persistent volumes, either to provision new volumes that are pre-populated with the snapshot data or to restore an existing volume to a previous state by using the snapshot capability of the Azure Disks CSI driver. For more information, see Volume snapshots.

  • Avoid disk striping across disks. We recommend that you avoid striping across multiple disks in Kubernetes.

  • Use PV/PVC. We recommend using PV and PVC in Kubernetes to dynamically create disks where required. For more information about persistent storage, see Storage options for applications in Azure Kubernetes Service (AKS).

Azure Files

For Azure Files, we recommend the following design options:

  • Choose Premium. If performance is critical, we recommend using the Premium tier.

  • Create dedicated storage accounts. We recommend providing dedicated storage accounts for your file shares.

  • Choose static or dynamically created file shares. We recommend careful consideration of whether you want AKS to create the file shares or if you want to create them statically outside of Kubernetes. Storage that is created dynamically can also be deleted dynamically. For more information about letting AKS dynamically create file shares, see Dynamically create and use a persistent volume with Azure Files.

Azure NetApp Files

For Azure NetApp Files, we recommend the following design options:

  • Choose a performance tier based on the application requirements. Azure NetApp Files offers 3 performance tiers that offer varying classes of performance. For more information, see Performance considerations for Azure NetApp Files.

  • Create capacity pools in the same Azure region as the AKS cluster. For more information, see Create a capacity pool for Azure NetApp Files.

  • Use the Auto QoS type for capacity pools.

  • Plan your network. Two options exist for network design:

    1. If you use the same VNet for AKS and Azure NetApp Files, create a dedicated subnet for Azure NetApp Files and delegate the subnet to Microsoft.NetApp/Volumes.
    2. If you use different VNets, establish VNet peering between them.

Blob storage

For blob storage, we recommend the following design options:

Next steps

Learn how to scope cost allocation to a deployment, a service, a label, a pod, or a namespace in AKS by using Kubecost.