Google IOT MQTT Sample

Overview

Based on the Zephyr sample, and adapted for nRF9160, leveraging modem features.

This sample application demonstrates a "full stack" application. This currently is able to:

• Establish a TLS connection with the Google IOT Cloud servers
• Publish data to the Google IOT Cloud
• Send/Receive keep alive / pings from cloud server

Requirements

• Entropy source
• Google IOT Cloud account
• Google IOT Cloud credentials and required information
• Cellular connectivity

Building and Running

This application has been built and tested on the Nordic nRF9160-DK. ECDSA keys are required to authenticate to the Google IOT Cloud. The application includes a key creation script.

Run bash create_keys.sh <device-id> in the samples/net/cloud/google_iot_mqtt/src/private_info/ directory.

Clone the cred utility for programming credentials to the modem.

Program the client private key:

python3 cred.py \
  --client_private_key <device-id>-ec_private.pem \
  --sec_tag 10

Download cloud-side certs (primary and backup)

• primary
• backup

Convert cloud-side certs from binary to text

openssl x509 -inform DER -outform PEM -in gtsltsr.crt -out gtsltsr.pem
openssl x509 -inform DER -outform PEM -in GSR4.crt -out GSR4.pem

NOTE: It is not necessary to change the certs to to "C-Style\n" formatting.

Program the cloud-side certs:

python3 cred.py \
  --CA_cert gtsltsr.pem \
  --sec_tag 202
python3 cred.py \
  --CA_cert GSR4.pem \
  --sec_tag 203

Assign keys on Google Cloud IoT Core

• Device Details -> Assign Public Key
• Input Method: Enter Manually
• Public key format: ES256
• Public key value: content of <device-id>-ec_public.pem

Users will also be required to configure the following Kconfig options based on their Google Cloud IOT project. The following values come from the Google Cloud Platform itself:

• PROJECT_ID: When you select your project at the top of the UI, it should have a "name", and there should be an ID field as well. This seems to be two words and a number, separated by hyphens.
• REGION: The Region shows in the list of registries for your registry. And example is "us-central1".
• REGISTRY_ID: Each registry has an id. This is a string given when creating the registry.
• DEVICE_ID: A name given for each device. When viewing the table of devices, this will be shown.

From these values, the config values can be set using the following template:

CLOUD_CLIENT_ID="projects/PROJECT_ID/locations/REGION/registries/REGISTRY_ID/devices/DEVICE_ID"
CLOUD_AUDIENCE="PROJECT_ID"
CLOUD_SUBSCRIBE_CONFIG="/devices/DEVICE_ID/config"
CLOUD_PUBLISH_TOPIC="/devices/DEVICE_ID/state"

See Google Cloud MQTT Documentation.