Fixing the Error and Key Not Found in the Key Ring Session Cookie Unprotection in C# Azure AKS Deployment

Troubleshooting Key Management and Session Cookie Issues in Azure AKS

When deploying a C# application on Azure Kubernetes Service (AKS), you may encounter issues related to key management and data protection. One such error is the "The key was not found in the key ring" exception, which is frequently coupled with "Error unprotecting the session cookie." This can be frustrating, especially when integrating services within a microservices architecture.

In our case, we are using the Docker image mcr.microsoft.com/dotnet/aspnet:8.0 to deploy the application. The external app running inside AKS is responsible for making HTTP connections to another service. However, the failure in data protection causes the session cookies to remain unprotected, leading to the key errors logged in Azure App Insights.

Efforts were made to set up the data protection system, including configuring it to use Azure Blob storage for key persistence. Despite following the official ASP.NET Core documentation for data protection, the application still throws errors, failing to pick up the key from the specified blob storage location.

Understanding the origin of these keys and the reason they are not found in the key ring is crucial to resolving this issue. This article will explore the root cause of the problem, outline key steps to investigate further, and provide potential solutions to ensure the data protection configuration is correctly implemented in your AKS deployment.

Understanding Data Protection and Key Management in Azure AKS

The scripts provided earlier serve a crucial role in resolving the "The key was not found in the key ring" error and the related "Error unprotecting the session cookie" issue in your C# application running on Azure Kubernetes Service (AKS). In the first script, we use the Data Protection API to persist keys to Azure Blob Storage. This configuration is necessary to ensure that the keys used to protect sensitive data, such as cookies, are stored securely outside the containerized application. The key method PersistKeysToAzureBlobStorage ensures the keys are available across multiple instances of your app, addressing the problem where the key ring isn’t found within the AKS pod.

We also use the SetApplicationName method, which is crucial in environments where multiple applications might share the same infrastructure. Setting a unique application name isolates your app’s key ring from others, preventing potential key conflicts. Another important method, SetDefaultKeyLifetime, defines the lifespan of a key, after which a new one is generated. This helps rotate encryption keys regularly, ensuring that data protection is up-to-date and minimizing the risk of key exposure due to long-lived keys.

The second script showcases an alternative approach using Redis to store Data Protection keys. The Redis approach is particularly useful in scenarios where you need a distributed key store with high availability. The ConnectionMultiplexer.Connect method establishes a connection to the Redis instance, and the PersistKeysToStackExchangeRedis method is used to persist the keys in Redis. This method is optimized for distributed environments where you have multiple replicas of your service running across different nodes, ensuring that all instances can access the same encryption keys securely.

To ensure that both the Blob and Redis configurations work correctly, unit tests are added in each script. These tests check whether the IDataProtectionProvider and IDistributedCache services are configured correctly in your ASP.NET Core application. By running these tests, you can validate that the Data Protection system is properly set up and that keys are stored and retrieved from the desired location. Testing is a crucial step, as it guarantees that the configuration changes are effective in different environments, thus resolving the issues related to key unavailability in Azure AKS deployments.

// Step 1: Configure Data Protection in Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddDataProtection()
            .PersistKeysToAzureBlobStorage(new Uri("<b>your-blob-uri</b>"))
            .SetApplicationName("<b>your-app-name</b>")
            .SetDefaultKeyLifetime(TimeSpan.FromDays(30));
    services.AddControllersWithViews();
}

// Step 2: Ensure that the Data Protection keys are created in Blob Storage
public class Startup
{
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        app.UseDataProtection();
        app.UseRouting();
        app.UseEndpoints(endpoints => { endpoints.MapControllers(); });
    }
}

// Step 3: Add Unit Tests to verify Data Protection configuration
[Fact]
public void DataProtection_IsConfiguredCorrectly()
{
    // Arrange
    var dataProtectionProvider = services.GetService<IDataProtectionProvider>();
    Assert.NotNull(dataProtectionProvider);
}

// Step 1: Configure Data Protection with Redis in Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    var redis = ConnectionMultiplexer.Connect("<b>redis-connection-string</b>");
    services.AddDataProtection()
            .PersistKeysToStackExchangeRedis(redis, "DataProtection-Keys");
    services.AddControllersWithViews();
}

// Step 2: Implement Redis Cache for Key Storage
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    app.UseRouting();
    app.UseEndpoints(endpoints => { endpoints.MapControllers(); });
}

// Step 3: Add Unit Tests to verify Redis Configuration
[Fact]
public void RedisKeyStorage_IsConfiguredCorrectly()
{
    // Arrange
    var redisCache = services.GetService<IDistributedCache>();
    Assert.NotNull(redisCache);
}

Troubleshooting Data Protection Key Persistence in Azure Kubernetes

One important aspect of troubleshooting the "key was not found in the key ring" error in Azure Kubernetes Service (AKS) is ensuring the environment’s configuration supports key persistence. By default, applications may not store keys locally, especially when deployed in ephemeral environments like containers. In such cases, it’s crucial to leverage external storage solutions, such as Azure Blob Storage or Redis, to ensure that the Data Protection keys persist across pod restarts.

An often overlooked element is how environment variables and application settings in Kubernetes play a role in enabling data protection. When deploying to AKS, it’s important to define key storage paths or connections (for Blob Storage or Redis) via configuration settings like `appsettings.json` or Kubernetes secrets. Without these configurations, the Data Protection system may fall back to its default behavior of attempting to persist keys in a non-existent local file system, leading to the error.

Another critical element is the proper setup of identity-based access for your application. For example, using Managed Identity in Azure enables secure access to external key storage like Blob Storage. Ensuring that your application’s identity has the appropriate permissions to read and write from Blob Storage or Redis is vital for the Data Protection system to work. If these permissions are missing, the keys won’t be stored or retrieved correctly, leading to runtime errors in your AKS-based application.