C# Operator SDK

The C# Operator SDK is a framework to build Kubernetes operators with C# and .NET Core.

Features

• Easy custom resource and controller definition as C# classes
• Custom resource event watchers at namespace and cluster scope
• Configurable retry-on-failure policy
• Smart concurrent event queues (inspired by Container Solution's article)
• Kubernetes graceful termination policy support

Usage

Setup a new .NET Core 3.1 project and add the C# Operator SDK package:

dotnet new console
dotnet add package k8s.Operators

Assuming that you have already added a custom resource definition for MyResource in your Kubernetes cluster, define a class deriving from CustomResource for the custom resource schema:

// Set the CRD attributes
[CustomResourceDefinition("example.com", "v1", "myresources")]
public class MyResource : CustomResource<MyResource.MyResourceSpec, MyResource.MyResourceStatus>
{
    // Define spec
    public class MyResourceSpec
    {
        public int property1 { get; set; }
        // :
    }

    // Define status
    public class MyResourceStatus
    {
        public int property2 { get; set; }
        // :
    }
}

Define a class deriving from Controller for the controller logic:

public class MyResourceController : Controller<MyResource>
{
    public MyResourceController(OperatorConfiguration configuration, IKubernetes client, ILoggerFactory loggerFactory = null) 
        : base(configuration, client, loggerFactory)
    {
    }

    protected override async Task AddOrModifyAsync(MyResource resource, CancellationToken cancellationToken)
    {
        Console.WriteLine($"Add/Modify {resource}");
        // :
        // Handle Add/Modify event
    }

    protected override async Task DeleteAsync(MyResource resource, CancellationToken cancellationToken)
    {
        Console.WriteLine($"Delete {resource}");
        // :
        // Handle Delete event
    }
}

Setup the operator in Main():

static async Task<int> Main(string[] args)
{
    // Create the Kubernetes client
    using var client = new Kubernetes(KubernetesClientConfiguration.BuildConfigFromConfigFile());

    // Setup the operator
    var @operator = new Operator(OperatorConfiguration.Default, client);
    @operator.AddControllerOfType<MyResourceController>();

    // Start the operator
    return await @operator.StartAsync();
}

Curiosity: Since operator is a reserved keyword in C#, it has been escaped with @operator.

Start the operator with:

dotnet run

In the /samples/basic directory you find a sample operator that simulates the interaction with an external service and can be used as a template for real-world operators.

Follow the instructions to run it locally and deploy it to Kubernetes.

Compiling the source code

git clone https://github.com/falox/csharp-operator-sdk.git
cd csharp-operator-sdk
dotnet restore
dotnet build

Running the tests:

dotnet test

References

• Jason Dobies and Joshua Wood, Kubernetes Operators, O'Reilly, 2020
• Radu Matei, Writing controllers for Kubernetes CRDs with C#, 2019