How to send notification from app engine to local application

[Juan Hoo]

Hi, 

I tried to find a way to send message from Google app engine to local application.

Here is my case, I have a servlet running in the GAE and a daemon application run local linux machine. Sometimes I need the servlet notify the local daemon to run some tasks immediately. 

Not sure whether a way to do that? Email is not a option.

What I found now is 

1. GCM/FCM support mobile device/web app but doesn't support windows/linux application.

2. Google app engine doesn't support listen. So I can not create connection between local application and GAE servlet.  Also the daemon is under firewall and can not listen either.

Are there any other way to achieve it? 

Thanks

[George (Cloud Platform Support)]

Hello Juan, 

You may choose to implement a topic, and have your daemon application subscribe to it. Google Cloud Pub/Sub provides reliable, many-to-many, asynchronous messaging between applications. Publisher applications can send messages to a topic, and other applications can subscribe to that topic to receive the messages. You may find more detail in the "Writing and Responding to Pub/Sub Messages" online document. 

[Juan Hoo]

Thanks for quick response. I read pub/sub topic before but didn't realize that it can be use in desktop application.

Will check again.

[Juan Hoo]

Hi George,

I tried to implement publisher on the my Server code (GAE). It worked. But it stop publishing any message today. I use pub/sub client code similar with example code in https://cloud.google.com/pubsub/docs/publisher. 

If I publish message through https://console.cloud.google.com on the topic, my client can receive the message without any problem.

Are there any issue with the publish code?

public static void publish(String message) throws Exception {

TopicName topicName = TopicName.of(projectId, topicId);


Publisher publisher = null;
List<ApiFuture<String>> messageIdFutures = new ArrayList<>();

try {
    publisher = Publisher.newBuilder(topicName).build();
    ByteString data = ByteString.copyFromUtf8(message);
    PubsubMessage pubsubMessage = PubsubMessage.newBuilder().setData(data).build();
    ApiFuture<String> messageIdFuture = publisher.publish(pubsubMessage);
    messageIdFutures.add(messageIdFuture);
}finally {
    List<String> messageIds = ApiFutures.allAsList(messageIdFutures).get();
    for (String messageId : messageIds) {
        System.out.println("published with message ID: " + messageId);

    }
    if (publisher != null) {
        // When finished with the publisher, shutdown to free up resources.
        publisher.shutdown();
    }

}

Thanks

On Monday, January 29, 2018 at 5:26:52 PM UTC-6, George (Cloud Platform Support) wrote: