NServiceBus Router backplane topology

Component: NServiceBus.Router
NuGet Package NServiceBus.Router (2.x)
This is a community maintained project
Target NServiceBus Version: 7.x

Two or more routers can be connected together to form a backplane topology.

Backplane

This setup often makes sense for geo-distributed systems. The following snippet configures the router hosted in the European part of the globally distributed system to route messages coming from outside via the Azure Storage Queues interface directly to the local endpoints and to route messages sent by local endpoints to either east or west United States through designated gateway routers.

The designated gateway concept is not related to the NServiceBus.Gateway package. When the designated gateway is specified in the route, the message is forwarded to it instead of the actual destination.
var routerConfig = new RouterConfiguration("Router.WestEurope");

routerConfig.AddInterface<MsmqTransport>("Endpoints", transportExtensions => { });
routerConfig.AddInterface<AzureStorageQueuesTransport>("Backplane", transportExtensions => { });

var staticRouting = routerConfig.UseStaticRoutingProtocol();

//Send all messages from the Backplane interface directly to the destination endpoints
staticRouting.AddRoute(
    (iface, destination) => iface == "Backplane",
    "From outside", null, "Endpoints");

//Send all messages to site WestUS through the Backplane interface via Router.WestUS
staticRouting.AddRoute(
    destinationFilter: (iface, destination) => destination.Site == "WestUS",
    destinationFilterDescription: "To West US",
    gateway: "Router.WestUS",
    iface: "Backplane");

//Send all messages to site EastUS through the Backplane interface via Router.EastUS
staticRouting.AddRoute(
    (iface, destination) => destination.Site == "EastUS",
    "To East US", "Router.EastUS", "Backplane");
As an example the routing rules here use the Site property that can be set through the SendOptions object when sending messages. The backplane topology does not require site-based routing and can be configured e.g. using endpoint-based convention like in the multi-way routing example.

To learn more about using the Router in the backplane topology, see the backplane sample which shows how parts of the system (a.k.a. services) that use their own SQL Server databases can be connected with a RabbitMQ-based backplane.

Case study: Geo-distributed system

When parts of a system are geographically distributed, the selected transport needs to work well across the public Internet. Unfortunately these transports tend to provide the lowest consistency guarantees. This makes it more difficult to ensure correctness of message handling code in all failure modes.

Instead of using the lowest common denominator transport for the whole system, the Router can be used to connect the transport on the inside (the one offering high consistency guarantees) with the transport on the outside (the one suitable for usage in the public Internet).

Case study: Sharding SQL Server transport

SQL Server transport offers some unique features such transaction sharing between publishing messages and accessing the data. This feature makes writing correct message handling logic easy as there are few failure modes. Either both publishing and updating data succeeds or none of them succeeds. Unfortunately it is not designed for high throughput systems.

Instead of switching to a different transport that offers higher throughput but provides lower consistency guarantees, the Router can be used to connect islands of SQL Server transport. This sharding approach works when most messages are exchanged within islands.

Samples


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