Fallback.cs

public async Task CreateOrderAsync(int basketId, Address shippingAddress)
{
    var basketSpec = new BasketWithItemsSpecification(basketId);
    var basket = await _basketRepository.GetBySpecAsync(basketSpec);

    Guard.Against.NullBasket(basketId, basket);
    Guard.Against.EmptyBasketOnCheckout(basket.Items);

    var catalogItemsSpecification = new CatalogItemsSpecification(basket.Items.Select(item => item.CatalogItemId).ToArray());
    var catalogItems = await _itemRepository.ListAsync(catalogItemsSpecification);

    var items = basket.Items.Select(basketItem =>
    {
        var catalogItem = catalogItems.First(c => c.Id == basketItem.CatalogItemId);
        var itemOrdered = new CatalogItemOrdered(catalogItem.Id, catalogItem.Name, _uriComposer.ComposePicUri(catalogItem.PictureUri));
        var orderItem = new OrderItem(itemOrdered, basketItem.UnitPrice, basketItem.Quantity);
        return orderItem;
    }).ToList();

    var order = new Order(basket.BuyerId, shippingAddress, items);
    await _db.AddAsync(order);
    await _db.SaveChangesAsync();

    var orderPlacedEvent = new OrderPlacedEvent(order.Id);
    var retry = Policy.Handle<Exception>()
        .WaitAndRetryAsync(new[] { TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(2), TimeSpan.FromSeconds(3) });

    var fallback = Policy.Handle<Exception>().FallbackAsync(async _ =>
    {
        var s3Client = new AmazonS3Client();
        await s3Client.PutObjectAsync(new PutObjectRequest
        {
            Key = Guid.NewGuid().ToString(),
            ContentBody = JsonConvert.SerializeObject(orderPlacedEvent)
        });
    });

    await fallback.WrapAsync(retry).ExecuteAsync(async () =>
    {
        await _broker.Publish(orderPlacedEvent);
    });
}