Tag Archives: HTTP WEBSITE_WARMUP_PATH

Swarm Space – DeviceClient Cache warming with HTTPTrigger

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For C2D messaging to work a device must have a DeviceClient “connection” established to the Azure IoT Hub which is a problem for irregularly connect devices. Sometimes establishing a connection on the first D2C messages is sufficient, especially for devices which only support D2C messaging. An Identity Translation Gateway establishes a connection for each device (see discussion about AMQP Connection multiplexing) so that C2D messages can be sent immediately.

I initially tried building a cache loader with BackgroundService so that the DeviceClient cache would start loading as the application started but interdependencies became problem.

public partial class Connector
{
    [Function("BumblebeeHiveCacheRefresh")]
    public async Task<IActionResult> BumblebeeHiveCacheRefreshRun([HttpTrigger(AuthorizationLevel.Function, "get")] CancellationToken cancellationToken)
    {
        _logger.LogInformation("BumblebeeHiveCacheRefresh start");

        await _swarmSpaceBumblebeeHive.Login(cancellationToken);

        foreach (SwarmSpace.BumblebeeHiveClient.Device device in await _swarmSpaceBumblebeeHive.DeviceListAsync(cancellationToken))
        {
            _logger.LogInformation("BumblebeeHiveCacheRefresh DeviceId:{DeviceId} DeviceName:{DeviceName}", device.DeviceId, device.DeviceName);

            Models.AzureIoTDeviceClientContext context = new Models.AzureIoTDeviceClientContext()
            {
                // TODO seems a bit odd getting this from application settings
                OrganisationId = _applicationSettings.OrganisationId, 
                //UserApplicationId = device.UserApplicationId, deprecated
                DeviceType = (byte)device.DeviceType,
                DeviceId = (uint)device.DeviceId,
            };

            switch (_azureIoTSettings.ApplicationType)
            {
                case Models.ApplicationType.AzureIotHub:
                    switch (_azureIoTSettings.AzureIotHub.ConnectionType)
                    {
                        case Models.AzureIotHubConnectionType.DeviceConnectionString:
                             await _azureDeviceClientCache.GetOrAddAsync<DeviceClient>(device.DeviceId.ToString(), (ICacheEntry x) => AzureIoTHubDeviceConnectionStringConnectAsync(device.DeviceId.ToString(), context));
                            break;
                        case Models.AzureIotHubConnectionType.DeviceProvisioningService:
                             await _azureDeviceClientCache.GetOrAddAsync<DeviceClient>(device.DeviceId.ToString(), (ICacheEntry x) => AzureIoTHubDeviceProvisioningServiceConnectAsync(device.DeviceId.ToString(), context, _azureIoTSettings.AzureIotHub.DeviceProvisioningService));
                            break;
                        default:

                        _logger.LogError("Azure IoT Hub ConnectionType unknown {0}", _azureIoTSettings.AzureIotHub.ConnectionType);

                            throw new NotImplementedException("AzureIoT Hub unsupported ConnectionType");
                    }
                    break;

                case Models.ApplicationType.AzureIoTCentral:
                    await _azureDeviceClientCache.GetOrAddAsync<DeviceClient>(device.DeviceId.ToString(), (ICacheEntry x) => AzureIoTHubDeviceProvisioningServiceConnectAsync(device.DeviceId.ToString(), context, _azureIoTSettings.AzureIoTCentral.DeviceProvisioningService));
                break;

                default:
                    _logger.LogError("AzureIoT application type unknown {0}", _azureIoTSettings.ApplicationType);

                    throw new NotImplementedException("AzureIoT unsupported ApplicationType");
            }
        }

        _logger.LogInformation("BumblebeeHiveCacheRefresh finish");

        return new OkResult();
    }
}

The HTTP WEBSITE_WARMUP_PATH environment variable is used to call the Azure HTTPTrigger Function and this is secured with an x-functions-key header.

Azure Function App Configuration

In the short-term loading the cache with a call to an Azure HTTPTrigger Function works but may timeout issues. When I ran the connector with my 100’s of devices simulator the function timed out every so often.