mqtt: PUBLISH: Pubsub topic missing

[Chris Wren]

I'm working through the sample at: 

https://github.com/GoogleCloudPlatform/python-docs-samples/tree/master/iot/api-client/mqtt_example

I have a registry:

  example-registry

 

with a topic:

  projects/project-id/topics/events

a subscription on that topic: 

  projects/project-id/subscriptions/my-sub

and a device

  my-rs256-device

but when I run the example it says: 

Publishing message 8/100: 'example-registry/my-rs256-device-payload-8'

Sending on topic /devices/my-rs256-device/events

Sending paylad example-registry/my-rs256-device-payload-8

('on_connect', 'Connection Accepted.')

('on_disconnect', '1: Out of memory.')

and the device console

   https://console.cloud.google.com/iot/locations/us-central1/registries/example-registry/devices/my-rs256-device?project= project-id/

says 

  mqtt: PUBLISH: Pubsub topic missing

web search doesn't seem to know about this error. 

clue welcome

[Tianzi Cai]

Have you created the Pub/Sub topic? You can check that by checking Pub/Sub>Topics in https://console.cloud.google.com. 

[Chris Wren]

It turns out that for iioT you need to both make the topic and then also map it to an mqtt topic.

at https://console.cloud.google.com/iot/locations/us-central1/registries/example-registry/edit?project=project-id

I needed to select the pubsub topics as the default telemetry topic and the default config topic.

This is detailed at the top of: https://cloud.google.com/iot/docs/how-tos/devices

but I skipped that part because I started following a different, out-of-date example and by the time I found the up-to-date one I'd already created my registry so I skipped it.

Hopefully this will become the search hit for the "mqtt: PUBLISH: Pubsub topic missing" error string, so that people can find out what they did wrong. 

thanks!

[Alex Hong]

Was the out-of-date example that you followed something that you accessed recently? 

Also, I was about to reply to this but I'm glad you managed to get it working in the end. I actually tried this example earlier today and managed to get it working (I think the interface for creating registries forces you to assign a telemetry topic now).

[Tianzi Cai]

Glad to hear it's working now too! I followed two QwikLabs to learn IoT Core myself. The step to create a Pub/Sub topic is somewhere in the lab. Providing the links to them: 

A Tour of Cloud IoT Core

Internet of Things: Qwik Start

Also, to quote `https://github.com/GoogleCloudPlatform/nodejs-docs-samples/blob/master/iot/mqtt_example/cloudiot_mqtt_example_nodejs.js` here: 

// The MQTT topic that this device will publish data to. The MQTT

// topic name is required to be in the format below. The topic name must end in

// 'state' to publish state and 'events' to publish telemetry. Note that this is

// not the same as the device registry's Cloud Pub/Sub topic.

const mqttTopic = `/devices/${argv.deviceId}/${argv.messageType}`;

[Chris Wren]

it was Arm-based IoT Kit for Cloud IoT Core. I already sent them some feedback about it. The command-line version of the registry creation left me without mqtt mappings. Maybe that's a bug in the command-line tool, if it's intended to enforce that? By "interface for creating registries" I assume you mean the web interface.

[Alex Hong]

Ah ok. Yeah, that does look a little out of date. And yes, I did mean the web interface (I attached a screenshot of the UI requiring you to select a telemetry topic).