Mqtt Topic in IOT Core

Question

Hi,

I have two out of four IoT devices successfully subscribing to my broker on the topic 'sdk/test/js'. They are working fine and receiving the messages as expected. After that, I created a second topic 'sdk/test/akm'. However, the other two devices are unable to subscribe to this new topic. Could this issue be related to certificates, or is there something else I'm missing?

Additionally, how do I create extra topics? I thought it was possible to do this by simply adding a "/" to the topic.

Thank you for your assistance!

ggainaru · Accepted Answer

Each device should have a unique certificate to authenticate with AWS IoT. When multiple devices use the same certificate, it might be a security breach.  
For the problematic device(s): go to IoT Core -> Things -> select the thing -> Certificates -> click on the attached certificate -> Policies -> click on the policy (default policy name: GreengrassV2IoTThingPolicy) -> check to have something similar to:
```
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "iot:Connect",
        "iot:Publish",
        "iot:Subscribe",
        "iot:Receive"
      ],
      "Resource": "*"
    }
  ]
}
```
Ressource line should be "*" (access to all topics, less secure but good for testing) or only the arn of the intended topic. Your current policy attached to the problematic devices might include only the arn of "sdk/test/js" which explains limited access to this topic only.

ggainaru · Answer

Please check the IoT policy attached to the new devices - does it include permissions to connect and subscribe to 'sdk/test/akm'?
- general guidance: https://docs.aws.amazon.com/iot/latest/developerguide/iot-policies.html
- example: https://docs.aws.amazon.com/iot/latest/developerguide/pub-sub-policy.html#pub-sub-specific-topic

Mqtt Topic in IOT Core

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