Configure PubSub storage

Orleans stream providers use a pub/sub rendezvous to connect producers and consumers. The grain storage provider named PubSubStore stores explicit subscription metadata used by the grain-based pub/sub implementation.

PubSubStore durability determines whether explicit subscription records survive loss of the cluster’s in-memory state:

• AddMemoryGrainStorage configured with the name PubSubStore is suitable for development and tests. Records are lost when the cluster state is lost.
• A durable grain storage provider preserves records across silo and cluster restarts, subject to that provider’s own availability and consistency.
• Implicit subscriptions are derived from grain metadata instead of being created as explicit subscription records.

Even with durable PubSubStore, an explicit consumer must call ResumeAsync after activation to attach its current observer instance. Conversely, durable event storage doesn’t make subscription records durable. Configure both layers according to the recovery requirement.

Azure Table Storage example

Managed identity with AddAzureTableGrainStorage is preferred:

var endpoint = new Uri(configuration["AZURE_TABLE_STORAGE_ENDPOINT"]!);
var credential = new DefaultAzureCredential();

hostBuilder.UseOrleans(siloBuilder =>
{
    siloBuilder.AddAzureTableGrainStorage(
        "PubSubStore",
        options => options.TableServiceClient =
            new TableServiceClient(endpoint, credential));
});

A connection string is also supported:

hostBuilder.UseOrleans(siloBuilder =>
{
    siloBuilder.AddAzureTableGrainStorage(
        "PubSubStore",
        options => options.TableServiceClient =
            new TableServiceClient(connectionString));
});

Use a stable Orleans service ID and the same durable storage configuration across cluster restarts. Changing service identity or deleting the backing table creates a logically new subscription registry.

Operational guidance

• Back up and monitor PubSubStore like other application metadata.
• Keep provider names stable. A provider rename changes stream identity from the pub/sub system’s perspective.
• Remove subscriptions with UnsubscribeAsync when they are no longer needed.
• Before replacing a PubSubStore, plan how existing explicit subscriptions will be recreated.

For the internal rendezvous and pulling-agent design, see Orleans streams implementation.