# Retry failed messages using ServicePulse

<!-- Version variant: core_9; default: [/samples/servicecontrol/retry-messages/index.md](/samples/servicecontrol/retry-messages/index.md) -->


This sample shows how to retry a failed message. The sample uses the [Learning Transport](/transports/learning/index.md) and a portable version of the Particular Service Platform tools. Installing ServiceControl is **not** required.




## Running the solution

Running the solution starts 3 console windows. Wait a moment until the ServicePulse window opens in the browser.

![service-pulse-fresh](service-pulse-fresh.png)

### Sender

The sender is a program that uses NServiceBus to send simple test messages.

Press <kbd>Enter</kbd> in the Sender console window to send one.

### Receiver

The receiver reads messages off a queue and processes them. By default, it runs in a fault simulation mode, which causes message processing to fail, including the one that has just been sent.

```cmd
fail: NServiceBus.MoveToError[0]
      Moving message '6e387659-ea6b-47ee-8223-b31b00aa3d9f' to the error queue 'error' because processing failed due to an exception:
      System.Exception: Simulated error.
         at SimpleMessageHandler.Handle(SimpleMessage message, IMessageHandlerContext context) in \servicecontrol\retry-messages\Core_9\Receiver\SimpleMessageHandler.cs:line 25
(...)
```

Press <kbd>t</kbd> to disable the fault simulation mode so that the message is processed correctly once retried.

```cmd
t
Fault mode disabled
```

### ServicePulse

Going back to the ServicePulse browser window, there is a notification on the dashboard about one failed message.

![service-pulse-dash-error](service-pulse-dash-error.png)

Click on the failure symbol to see the datails. You can inspect the message headers as well as the payload.

![service-pulse-error-details](service-pulse-error-details.png)

Now click `Request retry` to initiate the message retry process i.e. sending the message back to the receiver's input queue for reprocessing.

![service-pulse-retry-in-progress](service-pulse-retry-in-progress.png)

Once the process is completed, go back to the Receiver console window.

![service-pulse-retry-completed](service-pulse-retry-completed.png)

### Receiver

You can now notice that the message has been successfully processed.

```cmd
t
Fault mode disabled
info: Toggle[0]
      Received message.
info: Toggle[0]
      Successfully processed message.
```

## Code walk-through

For simplicity, both [the immediate](/nservicebus/recoverability/index.md#immediate-retries) and [the delayed retries](/nservicebus/recoverability/index.md#delayed-retries) are disabled in the sample. As a result, messages are moved to the error queue after a single failed processing attempt:

<!-- snippet: DisableRetries -->

```cs
var recoverability = endpointConfiguration.Recoverability();

recoverability.Delayed(
    customizations: retriesSettings =>
    {
        retriesSettings.NumberOfRetries(0);
    });
recoverability.Immediate(
    customizations: retriesSettings =>
    {
        retriesSettings.NumberOfRetries(0);
    });
```

<!-- endsnippet -->

The receiver's failure mode is controlled by the `FaultMode` property. When `true` processing of `SimpleMessage` messages ends with an exception.

<!-- snippet: ReceiverHandler -->

```cs
_logger.LogInformation("Received message.");
if (FaultMode)
{
    throw new Exception("Simulated error.");
}
_logger.LogInformation("Successfully processed message.");
return Task.CompletedTask;
```

<!-- endsnippet -->