ForbiddenException error when using the boto3 publish method with IoTDataPlane

Question

I'm attempting to publish to an IoT topic within a lambda using the publish method for the boto3 IoTDataPlane client. However when I invoke the lambda, I get the following exception:

[ERROR] ClientError: An error occurred (ForbiddenException) when calling the Publish operation: None

I have also added an AWS IoT policy to the lambda.

**Here's a snippet of the lambda:**
```
import boto3
import json
import logging

logger = logging.getLogger(__name__)
logger.setLevel("DEBUG")

iot_client = boto3.client('iot', region_name='us-east-1')
endpoint_response = iot_client.describe_endpoint(endpointType='iot:Data-ATS')
endpoint_url = f"https://{endpoint_response['endpointAddress']}"
logger.debug(endpoint_url)
client = boto3.client('iot-data', region_name='us-east-1', endpoint_url=endpoint_url)

def handler(event, context):
    topic = "test/topic"
    datum = json.dumps({"a": "b"})
    logger.debug(datum)

response = client.publish(
        topic=topic,
        qos=0,
        payload=datum,
        retain=True
    )

logger.debug(response)
```

**And this is the policy statement associated with the lambda:**
```
self._handler.add_to_role_policy(
    iam.PolicyStatement(
        actions=[
            "iot-data:Publish",
            "iot-data:Close",
            "iot-data:AttachPolicy",
            "iot-data:ListNamedShadowsForThing",
            "iot:DescribeEndpoint"
        ],
        resources=[
            "*"
        ],
    )
)
```

Accepted Answer

Hi. I can see why you might assume there is, but there's no **iot-data** service. You can replace all **iot-data** references in the policy with just **iot**. Then you'll be able to publish. BTW, there's no **iot:Close** action.

Additionally (if the Lambda is in the same account and region as the IoT Core endpoint you want to use), you don't have to explicitly set the endpoint or the region so you could reduce the code down to something like:

```
import boto3
import json
import logging

logger = logging.getLogger(__name__)
logger.setLevel("DEBUG")

client = boto3.client('iot-data')

def handler(event, context):
    topic = "test/topic"
    datum = json.dumps({"a": "b"})
    logger.debug(datum)

response = client.publish(
        topic=topic,
        qos=0,
        payload=datum,
        retain=True
    )

logger.debug(response)
```

Then you could delete the **DescribeEndpoint** action from the policy too. And presently, you aren't using the **ListNamedShadowsForThing** or **AttachPolicy** actions so these could be deleted too (but you probably know that).

ForbiddenException error when using the boto3 publish method with IoTDataPlane

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