Tenant Routing

ID: transport.tenant-routing Maturity: GA

Summary

ITenantRoutingStrategy lets inbox and outbox transport dispatchers compute a publish route from durable tenant metadata without coupling transport packages to inbox or outbox abstractions.

Public Surface

public interface ITenantRoutingStrategy
{
    string ResolveRoute(string? tenantId, string contractName, string? topic);
}

The arguments have stable roles:

Argument	Value
`tenantId`	Durable envelope tenant, or null for an unscoped message
`contractName`	Stable message contract name and version-independent route identity
`topic`	Outbox topic when present; inbox dispatch passes the contract name as its topic hint

The return value becomes TransportPublishRequest.Route. The dispatcher keeps TransportPublishRequest.Destination equal to its configured DefaultDestination.

Resolution Order

When an ITenantRoutingStrategy is registered, it has first priority.

Without a strategy, inbox dispatch resolves the route in this order:

TransportInboxDispatcherOptions.ResolveRoute.
InboxEnvelope.ContractName.

Without a strategy, outbox dispatch resolves the route in this order:

OutboxEnvelope.Topic when non-empty.
TransportOutboxDispatcherOptions.ResolveRoute.
OutboxEnvelope.ContractName.

For example, a strategy can route tenant-east order events to tenant-east.orders.priority while every publish still targets the configured orders destination.

Register one ITenantRoutingStrategy in the application dependency container. LiteBus.Inbox.Dispatch and LiteBus.Outbox.Dispatch resolve it as an optional dependency. Broker-specific transport packages do not define tenant policy.

public sealed class TenantRouteStrategy : ITenantRoutingStrategy
{
    public string ResolveRoute(string? tenantId, string contractName, string? topic)
    {
        var partition = string.IsNullOrWhiteSpace(tenantId) ? "shared" : tenantId;
        return $"{partition}.{topic ?? contractName}";
    }
}

Packages

Package	Role
`LiteBus.Transport.Abstractions`	Declares `ITenantRoutingStrategy`
`LiteBus.Inbox.Dispatch`	Applies the strategy to inbox transport routes
`LiteBus.Outbox.Dispatch`	Applies the strategy to outbox transport routes

Invariants

Tenant routing is optional.
The strategy changes the route and cannot replace the configured transport destination.
Tenant metadata can still propagate through TransportHeaders.TenantId without a routing strategy.
Processor tenant leasing uses InboxProcessorOptions.TenantId or OutboxProcessorOptions.TenantId; it does not call the transport strategy.

Non-Goals

Tenant discovery from host context.
Tenant authorization.
Processor lease filtering.
Per-tenant broker connection pools.

Observability

Tenant identifiers are not metric tags because tenant counts can create unbounded cardinality. Inspect the selected transport route in adapter activities and logs. Use manager tenant filters for durable queue inspection.

Test Coverage

TransportInboxDispatcherTests.DispatchAsync_WithTenantRoutingStrategy_ShouldUseResolvedRoute verifies the inbox dispatcher passes tenant and contract metadata to the strategy and publishes the returned route.
TransportOutboxDispatcherTests.DispatchAsync_WithTenantRoutingStrategy_ShouldUseResolvedRoute verifies the outbox dispatcher passes tenant, contract, and topic metadata and publishes the returned route.
Broker dispatch integration tests verify canonical tenant-id header propagation independently of custom routing.