GPSTracker

GPS Device Tracker

This sample demonstrates a service for tracking GPS-equipped IoT devices on a map. Device locations are updated in near-real-time using SignalR and hence this sample demonstrates one approach to integrating Orleans with SignalR. The device updates originate from a device gateway, which is implemented using a separate process which connects to the main service and simulates a number of devices moving in a pseudorandom fashion around an area of San Francisco.

Data flows around the system as follows:

• A device gateway sends periodic location updates to a per-device DeviceGrain
• The DeviceGrain updates a singleton PushNotifierGrain with its location
• The PushNotifierGrain collects these updates into batches and pushes them to IRemoteLocationHub instances which it discovers by periodically polling the singleton HubListGrain
• HubListGrain maintains a list containing an IRemoteLocationHub reference for each host which is connected to to the Orleans cluster
• Each host has a HubListUpdater instance, which implements BackgroundService and periodically updates HubListGrain with its local IRemoteLocationHub reference.
• The RemoteLocationHub class which implements IRemoteLocationHub has an instance of IHubContext<LocationHub> injected into its constructor. This allows it to send messages to the Web clients which have connected to the LocationHub.

The following diagram is a representation of the above description:

The following an example of how this might look with multiple hosts and many browsers. Note that the PushNotifierGrain and HubListGrain are singletons and therefore there is one instance of each of those grains shared by the cluster. Singleton grains are a pattern in Orleans whereby only a single grain of a given type is accessed, for example by always calling the instance with a key 0 or Guid.Empty or some other fixed value, depending on if the grain is a IGrainWithIntegerKey or IGrainWithGuidKey. For example, each DeviceGrain gets an instance of the IPushNotifierGrain with id 0:

var notifier = GrainFactory.GetGrain<IPushNotifierGrain>(0);

Running the sample

Open three terminal windows. In the first terminal window, run the following at the command prompt:

dotnet run --project GPSTracker.Service

In the second terminal, launch another instance of the host, specifying that it's the second host by passing an InstanceId value as follows:

dotnet run --project GPSTracker.Service -- --InstanceId 1

Now open a web browser to http://localhost:5001/index.html. At this point, there will be no points moving around the map.

In the third terminal window, run the following at the command prompt to begin simulating devices:

dotnet run --project GPSTracker.FakeDeviceGateway

Dots will appear on the map in the Web browser and begin moving randomly around the area.