Dynamic routes are not re-created after cache is cleared - drupal

Question

I am trying to create the dynamic routes based on the data pulled from third party service which is also another Drupal website. The routes are created when the custom module holding this dynamic routes is enabled but these dynamic routes are not re-created when cache is cleared. The source Drupal website exposes Drupal content and this target site needs to create routes with the path alias from the source Drupal site.
Any guide/tips for better implementation would be highly appreciated.
This is how i created dynamic routes:
<?php
namespace Drupal\demo_module\Routing;
use Symfony\Component\Routing\Route;
/**
* Defines dynamic routes.
*/
class DynamicRoutes {
/**
* {#inheritdoc}
*/
public function routes() {
$routes = [];
// This is the service for pulling data. It pulls data from another drupal sites.
$demoService = \Drupal::service('demo_module.service');
// Just checks if service is available.
if ($demoService->isAvailable()) {
try {
$demoData = $demoService->getDataFromServices();
if (isset($demoData['data']) && count($demoData['data']) > 0) {
foreach ($demoData['data'] as $data) {
$alias = $data['attributes']['path']['alias'];
if (isset($alias) && !empty($alias)) {
$route_provider = \Drupal::service('router.route_provider');
$routeName = 'demo_module.' . ltrim($alias, '/');
$exists = count($route_provider->getRoutesByNames([$routeName])) === 1;
if (!$exists) {
// Want to add .pdf at the end of route name. So the route name would be the path alias from the source drupal site plus .pdf appended.
$routes[$routeName] = new Route(
'/' . $alias . '.pdf',
[
'_controller' => '\Drupal\demo_module\Controller\DemoModuleController::getData',
'_title' => 'Demo Data',
],
[
'_permission' => 'access content',
]
);
}
}
}
}
}
catch (\Exception $e) {
throw new \Exception($e->getMessage());
}
}
return $routes;;
}
}
This is how routes were added to demo_module.routing.yml
route_callbacks:
- '\Drupal\demo_module\Routing\DynamicRoutes::routes'

Answer 1

It seems routes are cached (and not cleared by clearing the caches??).
Judging by the docs here, you can set the routes not to cache.
eg.
$routes[$routeName] = new Route(
'/' . $alias . '.pdf',
[
'_controller' => '\Drupal\demo_module\Controller\DemoModuleController::getData',
'_title' => 'Demo Data',
],
[
'_permission' => 'access content',
],
[
'no_cache' => TRUE
]
);
I did not test the code above, but it's the first thing I would try, Route class docs here