Shared SignalR HubConnection for multiple BackgroundServices in .NET

Question

My .NET BackgroundService application have multple workers and all of them connects to the same SignalR Hub. Each worker gets a unique ConnectionId which will not work in my case.

How, if possible, can I share the HubConnection between all of the workers to prevent different ConnectionIds?

Answer 1

I found a solution that solves my issue. I've created a HubService which every worker dependency inject and then calls EnsureConnectionEstablished() to make sure the connection is established.

public class HubService
{
        private readonly ILogger<SystemHealthWorker> _logger;
        private readonly ConfigurationService _config;
        private HubConnection _connection;

        public HubService(ILogger<SystemHealthWorker> logger, ConfigurationService configService)
        {
            _logger = logger;
            _config = configService;
        }

        public async Task<bool> EnsureConnectionEstablished()
        {
            _logger.LogDebug("Ensures that the hub connection is established.");

            if (_connection == null || _connection.State == HubConnectionState.Disconnected)
            {
                _logger.LogDebug("Hub connection is not established.");

                var config = await _config.GetConfiguration();
                if (config == null || string.IsNullOrEmpty(config.ServerAddress?.ToString()))
                {
                    throw new Exception("Invalid config. Hub connection will not be established.");
                }
                else if (string.IsNullOrWhiteSpace(config.AccessToken))
                {
                    throw new Exception("Invalid access token.");
                }

                var hubUrl = new Uri(config.ServerAddress);
                _logger.LogInformation($"Connecting to hub ({hubUrl})");

                _logger.LogDebug("Building hub connection.");
                _connection = new HubConnectionBuilder()
                .WithUrl(hubUrl, options => { options.AccessTokenProvider = () => Task.FromResult(config.AccessToken); })
                .WithAutomaticReconnect(new[] { TimeSpan.FromSeconds(0), TimeSpan.FromSeconds(15), TimeSpan.FromSeconds(30), TimeSpan.FromSeconds(60), TimeSpan.FromSeconds(120) })
                .Build();

                _connection.Reconnecting += OnReconnecting;
                _connection.Reconnecting += OnReconnected;
                _connection.Closed += OnClosed;

                await _connection.StartAsync();

                _logger.LogInformation($"Connected to hub with id {_connection.ConnectionId}.");
            }

            return _connection?.State == HubConnectionState.Connected;
        }
 }