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Stateful workloads in Azure Kubernetes Service (AKS)

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This article provides an overview of running stateful workloads on Azure Kubernetes Service (AKS).

What are stateful workloads?

A stateful workload is an application that uses persistent data storage to preserve state across multiple instances, ensuring a seamless and personalized user experience. This design is vital for services like online banking, online shopping, and email, where data consistency, session history, and reliability are crucial. Stateful workloads also offer efficiency in high performance and near real-time processing scenarios that benefit from advanced features like failover and recovery, ensuring business continuity.

While stateful workloads offer many benefits, they also present certain challenges. For example, stateful workloads often introduce complex processing patterns that can lead to increased overhead and performance costs. It's important that you understand and consider the specific needs of your application to help determine the right balance between statefulness and statelessness.

Given the critical role of stateful workloads, Azure provides several approaches for running them effectively. This section outlines best practices for deploying stateful workloads on Azure Kubernetes Service (AKS), helping developers and organizations choose the most suitable option for their needs.

Kubernetes stateful framework foundation stack

The Kubernetes stateful framework begins with a common foundation stack. In this case, we use the KATE stack, a popular, standardized stack used for many infrastructure projects. The KATE stack uses the following open-source tools:

The AKS guides don't implement ArgoCD or Terraform because they're designed for Day 1 operations. However, as your deployment scales and requirements evolve, it should be easier for you to integrate ArgoCD and Terraform since the guides use part of the KATE stack.

Kubernetes stateful framework for Az

With the foundation stack established, we now need to enhance the framework to support stateful workloads on Azure, specifically by integrating the essential resources for running data infrastructure on Azure Kubernetes Service (AKS).

Supporting complex stateful workloads, such as databases or message queues, requires storage capabilities that exceed ephemeral options. Specifically, we need systems that offer increased resilience and availability to address various events, such as application failures or workload reassignments to different hosts. We can achieve this using the PersistentVolume subsystem, which comprises three interconnected Kubernetes resources: PersistentVolumes, PersistentVolumeClaims, and StorageClasses. This subsystem provides an API for users and administrators to abstract the details of how storage is provided from how the storage is consumed.

Most stateful workloads need data from secrets, such as connection strings, usernames, passwords, and certificates. Azure Key Vault provides a secure store for secrets that we use to hold the necessary stateful frameworks secrets.

We also need a Kubernetes Controller or Kubernetes Operator, like the Secrets Store CSI Driver or the External Secrets Operator to synchronize secret store secrets as Kubernetes Secrets.

Screenshot of a diagram showing the Kubernetes stateful framework for Azure.

Design and deploy stateful workloads on Azure

The following sections provide links to design and deployment information for stateful workload scenarios on Azure.

MongoDB

PostgreSQL

Valkey

Contributors

Microsoft maintains this article. The following contributors originally wrote it:

  • Don High | Principal Customer Engineer
  • Colin Mixon | Product Manager
  • Erin Schaffer | Content Developer 2