C# Academy · Lesson

Error Handling and Retries

Handle faults with retry and dead-letter queues.

Error Handling and Retries is a free C# Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C# Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Failure Is Normal

Consumers fail: a transient database error, a downstream timeout, a bug on bad data. MassTransit provides layered tools (retry, redelivery, error queues) so failures are handled gracefully instead of losing messages.

Immediate Retry

For brief blips, configure retry so MassTransit reprocesses the message a few times in quick succession before giving up.

cfg.ReceiveEndpoint("orders", e =>
{
    e.UseMessageRetry(r => r.Immediate(3));
    e.ConfigureConsumer<OrderConsumer>(context);
});

Interval And Exponential Retry

Spacing retries helps when recovery takes longer. Use intervals or exponential backoff, similar to Polly.

e.UseMessageRetry(r =>
    r.Exponential(5,
        minInterval: TimeSpan.FromSeconds(1),
        maxInterval: TimeSpan.FromMinutes(1),
        intervalDelta: TimeSpan.FromSeconds(2)));

Filtering Which Errors Retry

Retry only transient exceptions; do not retry on permanent ones like validation failures. Use Handle and Ignore to scope retries.

e.UseMessageRetry(r =>
{
    r.Handle<TimeoutException>();
    r.Ignore<ValidationException>();
    r.Immediate(3);
});

Retry vs Redelivery

Retry keeps the message in memory and reprocesses quickly. Redelivery (delayed/second-level retry) returns the message to the broker to be delivered again much later, freeing the consumer in the meantime.

e.UseDelayedRedelivery(r =>
    r.Intervals(TimeSpan.FromMinutes(5),
                TimeSpan.FromMinutes(15),
                TimeSpan.FromMinutes(30)));

Combining Both Layers

A robust setup uses immediate retry for blips and delayed redelivery for longer outages. Configure redelivery outside retry so each redelivery attempt also gets its own immediate retries.

e.UseDelayedRedelivery(r => r.Intervals(
    TimeSpan.FromMinutes(5), TimeSpan.FromMinutes(15)));
e.UseMessageRetry(r => r.Immediate(3));

The Error Queue

When all retries and redeliveries are exhausted, MassTransit moves the message to an error queue (named <queue>_error). The message is preserved with exception details for investigation, never silently dropped.

Faults

On failure MassTransit also publishes a Fault<T> event. Other services can consume faults to alert, log, or trigger compensation.

public class OrderFaultConsumer : IConsumer<Fault<OrderPlaced>>
{
    public Task Consume(ConsumeContext<Fault<OrderPlaced>> context)
    {
        // inspect context.Message.Exceptions
        return Task.CompletedTask;
    }
}

Idempotency Matters

Because retries and redelivery can process a message more than once, consumers must be idempotent: handling the same message twice must not double-charge or duplicate work. Use unique ids and dedup checks.

Replaying From The Error Queue

After fixing a bug, you can move messages from the error queue back to the original queue to reprocess them, recovering work that previously failed.

Dead Letter And Skipped Queues

MassTransit also uses a skipped queue (_skipped) for messages no consumer wanted, helping you spot misrouted or unexpected message types in production.

Quick Check

Test error handling and retries.

Recap

MassTransit layers failure handling: retry (immediate/exponential, scoped with Handle/Ignore) for blips, redelivery for longer outages, and an error queue for exhausted messages plus Fault<T> events for alerting. Because messages can be processed more than once, keep consumers idempotent, and replay from the error queue after fixing bugs.

Frequently asked questions

Is the “Error Handling and Retries” lesson free?

Yes — the full text of “Error Handling and Retries” is free to read here on the web, and the C# Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C# Academy course, upgrade to CoddyKit PRO.

What will I learn in “Error Handling and Retries”?

Handle faults with retry and dead-letter queues. You practise C# Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C# Academy?

No prior experience is required. C# Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Error Handling and Retries” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C# Academy lesson?

Yes. Every C# Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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