Grain interface versioning

In this article, you learn how to use grain interface versioning. The versioning of grain state is out of scope.

Overview

On a given cluster, silos can support different versions of a grain type.

In this example, the client and Silo3 were compiled with grain interface A version 1. Silo 4 was compiled with A version 2.

Limitations

• No versioning on stateless workers.
• Streaming interfaces aren’t versioned.

Enable versioning

If you don’t explicitly add the version attribute to the grain interface, the grain has a default version of 0. You can version a grain by using the VersionAttribute on the grain interface:

[Version(X)]
public interface IVersionUpgradeTestGrain : IGrainWithIntegerKey
{
}

Where X is the version number of the grain interface, which is typically monotonically increasing.

Grain version compatibility and placement

When a call from a versioned grain arrives in a cluster:

• If no activation exists, Orleans creates a compatible activation.
• If an activation exists:
  • If the current activation isn’t compatible, Orleans deactivates it and creates a new compatible one (see Version selector strategy).
  • If the current activation is compatible (see Compatible grains), Orleans handles the call normally.

By default:

• All versioned grains are assumed to be backward-compatible only (see Backward compatibility guidelines and Compatible grains). This means a v1 grain can make calls to a v2 grain, but a v2 grain cannot call a v1 grain.
• When multiple versions exist in the cluster, Orleans randomly places the new activation on a compatible silo.

You can change this default behavior via GrainVersioningOptions:

var builder = Host.CreateApplicationBuilder(args);
builder.UseOrleans(siloBuilder =>
{
    siloBuilder.Configure<GrainVersioningOptions>(options =>
    {
        options.DefaultCompatibilityStrategy = nameof(BackwardCompatible);
        options.DefaultVersionSelectorStrategy = nameof(MinimumVersion);
    });
});

using var host = builder.Build();
await host.RunAsync();