Retryer Middleware

The Retryer Middleware is built-in middleware that gives you capability to retry the handling of an intent.

How to use it

As for any Middleware, you can use it by adding it to the bus instance.

const commandBus = createCommandBus<CommandHandlerRegistry>();
commandBus.useRetryerMiddleware({
    maxAttempts: 5;
    waitingAlgorithm: 'exponential',
    multiplier: 1.5;
    jitter: 0.5;
});

Remember built-in middlewares are intent aware, therefore you can customize the behavior per intent using the key intents.

Explanation

The Retryer middleware is going to catch the execution and re-run the following middleware until the maxAttempts is reached. Between each attempt, the middleware is going to wait for a certain amount of time. The waitingAlgorithm can be exponential, fibonacci, or none.

• jitter is a value between 0 and 1 that will add some randomness to the waiting time.
• multiplier is the factor to multiply the waiting time between each attempt. (only used for exponential)

Internally, the retryer middleware will keep a registry of sleeper if you decide to have different configuration per intent.

Error Stamps

Retryer Middleware will also retry the handling of the intent if it finds more error stamps than before. Some handlers might not throw exceptions but add error stamps to the result. A good example would be a lock middleware that would add an error stamp if the lock is not acquired.

Added Stamps

The Retryer Middleware is going to add:

• type RetriedStamp = Stamp<{ attempt: number; errorMessage: string }, 'missive:retried'>;

  Every time the middleware retries the handling of the intent.

Going further

Look at the code of the Retryer Middleware