I’m trying to implement ‘Fallback’ functionality (try a different endpoint if the original one fails) using the async-http-client library. The below code is functional and works locally, tested against a small set of requests.

    request.execute(new AsyncCompletionHandler<Object>() {
                    
        @Override
        public State onStatusReceived(HttpResponseStatus responseStatus) throws Exception {
            if(responseStatus.getStatusCode() != 201) {
                return State.ABORT;
            }
            return super.onStatusReceived(responseStatus);
        }
          
        @Override
        public Object onCompleted(Response response) throws Exception {

            if(response != null) {
                System.out.println("Main Sent sucessfully");
            }
            //If response is null meaning, getStatusCode != 201
            else {
                BoundRequestBuilder fallbackRequest = asynClient.preparePost(fallbackUrl).setBody("test");
                Future<Response> responseFuture = fallbackRequest.execute();
                Response rsp = responseFuture.get();
                System.out.println("Sent - RESPCODE: [" + rsp.getStatusCode() + "]");
            }

            return response;
        }
    
    });

My concern is with sending a blocking request in the onCompleted handler. Even though it works locally on my machine, not confident if it is appropriate for a high load environment.

Below documentation in the AsyncHandler<T> further reduces confidence.

 * Do NOT perform any blocking operation in there, typically trying to send another request and call get() on its future.
 * There's a chance you might end up in a dead lock.
 * If you really to perform blocking operation, executed it in a different dedicated thread pool.

Any suggestions on alternative techniques to implement fallback using the same library?