Broadcast events between processes

When trains run on worker processes and clients subscribe on the hub (the API and scheduler), the hub only hears about runs it executes itself until every process shares a broadcaster. Each process calls UseBroadcaster with the same RabbitMQ connection and exchange.

1. Add the transport to the hub

using Trax.Api.GraphQL.Extensions;
using Trax.Effect.Broadcaster.RabbitMQ.Extensions;
using Trax.Effect.Data.Postgres.Extensions;
using Trax.Effect.Extensions;
using Trax.Mediator.Extensions;
using Trax.Scheduler.Extensions;
 
var builder = WebApplication.CreateBuilder(args);
var connectionString = builder.Configuration.GetConnectionString("Trax")!;
var rabbitMq = builder.Configuration.GetConnectionString("RabbitMq")!;
 
builder.Services.AddTrax(trax => trax
    .AddEffects(effects => effects
        .UsePostgres(connectionString)
        .UseBroadcaster(b => b.UseRabbitMq(rabbitMq))
    )
    .AddMediator(typeof(Program).Assembly)
    .AddScheduler()
);
 
builder.Services.AddTraxGraphQL();
 
builder.Build().Run();

AddTraxGraphQL() sees the receiver UseBroadcaster registered and forwards what arrives to subscriptions. No other setting is needed.

2. Add the same transport to each worker

using Trax.Effect.Broadcaster.RabbitMQ.Extensions;
using Trax.Effect.Data.Postgres.Extensions;
using Trax.Effect.Extensions;
using Trax.Mediator.Extensions;
using Trax.Scheduler.Extensions;
 
var builder = WebApplication.CreateBuilder(args);
var connectionString = builder.Configuration.GetConnectionString("Trax")!;
var rabbitMq = builder.Configuration.GetConnectionString("RabbitMq")!;
 
builder.Services.AddTrax(trax => trax
    .AddEffects(effects => effects
        .UsePostgres(connectionString)
        .UseBroadcaster(b => b.UseRabbitMq(rabbitMq))
    )
    .AddMediator(typeof(Program).Assembly)
);
 
builder.Services.AddTraxWorker(opts => opts.WorkerCount = 4);
 
builder.Build().Run();

3. Check every host connected

A host that cannot reach the broker, or that the broker refuses (a wrong user or password), still starts and runs its trains, and keeps retrying; nothing crosses between processes in the meantime. Look for RabbitMQ receiver started on exchange trax.lifecycle in each host's startup log, and give every host a user the broker has.

4. Give each application its own exchange

Every process bound to an exchange receives everything published to it. When two applications share a broker, set a distinct ExchangeName (or use a vhost each):

.UseBroadcaster(b => b.UseRabbitMq(rabbitMq, opts => opts.ExchangeName = "billing.lifecycle"))

SDK Reference

UseBroadcaster | UseRabbitMq | AddTraxGraphQL | AddTraxWorker