tbd-develop / Mediator.Outbox

Outbox core with background service for processing along with SqlServer implmentation of outbox

Mediator Outbox

The outbox pattern is a useful pattern for resilience in your messaging. This implementation based on the Mediator library is intended to place INotification messages produced in the application into a queue for later processing.

Usage

In your code, where you would normally use IPublisher, or IMediator with Publish, you would instead replace this with INotificationPublisher. This is a new interface is functionally compatible with IPublisher interface for Publish.

In Memory Outbox, no processing

This is pretty much a useless implementation, as nothing will be done with messages and they exist only in your application.

ServiceCollection.AddMediatorOutbox(configure => 
    configure.UseInMemoryOutbox()
    );

In Memory Outbox, with processing

This is a more useful implementation, as it will process messages in the background. This is useful for testing, but you're basically getting the same behavior as the default Mediator implementation.

ServiceCollection.AddMediatorOutbox(configure => 
    configure
        .UseInMemoryOutbox()
        .WithBackgroundProcessing()
    );

SqlServer Outbox with/without processing

This is a more useful implementation, it will persist messages to a SqlServer database. And you can optionally enable processing in the background. This could also provide you the ability to only process on a single server of your application in a cluster if you enable processing on one server.

ServiceCollection.AddMediatorOutbox(configure => 
    configure
        .UseSqlServerOutbox("connection string")
        .WithBackgroundProcessing()
    );

Once you have the application built, to make sure the table exists when starting up, you now need to call ConfigureSqlOutbox. eg.

var app = builder.Build();

app.ConfigureSqlOutbox();

This will run the necessary migration to create the table in the database specified with your "domain.outbox" connection.

Processing Configuration

When using the background processing, you can configure process timeouts and whether exceptions should retry.

ServiceCollection.AddMediatorOutbox(configure => 
    configure
        .UseSqlServerOutbox("connection string")
        .WithBackgroundProcessing(x => 
            x.WithSettings(s => {
                s.Interval = TimeSpan.FromSeconds(5)
                s.BackOffOnException = TimeSpan.FromSeconds(5);
                s.MaximumBackOff = TimeSpan.FromSeconds(60);
                s.ShutdownOnException = true;
            }))
    );

Defaults;

• Interval = 5 seconds
• BackOffOnException = 5 seconds
• MaximumBackOff = 60 seconds
• ShutdownOnException = false

Issues

• The SqlServer implementation is not yet complete. It is not yet possible to configure the table name