title: Pause or slow down considerably Flink (Kafka) source until dependencies are ready
body: <p>I'm designing a Flink job that basically it's going to:</p>
  <ul>
  <li>Read messages from Kafka</li>
  <li>Process the incoming messages' data by requesting some more information from external services — for instance, make some HTTP/gRPC calls, retrieve some data, do some aggregation and store some partial results in a database</li>
  <li>Propagate results into Elasticsearch</li>
  </ul>
  <p>What I don't have clear is how to slow down, or completely pause the Flink job from reading Kafka messages whenever one of the (RESTful / gRPC) services is down, or simply decreasing their performance.</p>
  <p>Is there a way to achieve this by using some configuration settings or some Flink built-in component?</p>