Unable to publish MQTT message to AWS iot Core with lambda function. Where lambda is connected to VPC. Using VPC enpoint we need to connect to IOT core and publish message

Question

I have created a lambda function. Where lambda is connected to VPC with two private subnet. Without using Nat Gateway   we need to create lambda function and publish a mqtt message to IoT core. 
We configured VPC endpoint to AWS iot core. Created private hosted zone but no use 
we are getting error like 
Timeout task

Below is the code we used to publish a message to mqt

```
import json
import boto3

client = boto3.client('iot-data', region_name='*******')

def lambda_handler(event, context):
    print(event)
    # TODO implement
    # Change topic, qos and payload
    response = client.publish(
        topic='esp32/sub',
        qos=1,
        payload=json.dumps({"foo":"bar"})
    )
    print(response)
    
    return {
        'statusCode': 200,
        'body': json.dumps('Published to topic')
    }
```

Accepted Answer

I tried it in an EC2 environment with AWS CLI.

```
aws iot-data publish --topic esp32/sub --payload '{"a":"b"}' --region ap-northeast-1 --debug
```

```
EndpointConnectionError: Could not connect to the endpoint URL: "https://data.iot.ap-northeast-1.amazonaws.com/topics/esp32%2Fsub"
2022-06-25 11:57:35,520 - MainThread - awscli.clidriver - DEBUG - Exiting with rc 255

Could not connect to the endpoint URL: "https://data.iot.ap-northeast-1.amazonaws.com/topics/esp32%2Fsub"
```

It seems to be trying to connect to the `data endpoint` instead of `data-ats endpoint`

It appears that only ats-data is provided for VPC endpoints.
https://docs.aws.amazon.com/iot/latest/developerguide/IoTCore-VPC.html

I was able to Publish correctly by explicitly specifying the endpoint.

```
aws iot-data publish --topic esp32/sub --payload '{"a":"b"}' --region ap-northeast-1 --debug --endpoint https://a2klze32u5vkt3-ats.iot.ap-northeast-1.amazonaws.com
```
```
2022-06-25 11:57:55,896 - MainThread - urllib3.connectionpool - DEBUG - https://a2klze32u5vkt3-ats.iot.ap-northeast-1.amazonaws.com:443 "POST /topics/esp32%2Fsub HTTP/1.1" 200 65
2022-06-25 11:57:55,897 - MainThread - botocore.parsers - DEBUG - Response headers: {'date': 'Sat, 25 Jun 2022 11:57:55 GMT', 'x-amzn-RequestId': '2740292f-48b4-3fca-2fe6-11f6bbfaf895', 'content-length': '65', 'content-type': 'application/json', 'connection': 'keep-alive'}
2022-06-25 11:57:55,897 - MainThread - botocore.parsers - DEBUG - Response body:
{"message":"OK","traceId":"2740292f-48b4-3fca-2fe6-11f6bbfaf895"}
2022-06-25 11:57:55,898 - MainThread - botocore.hooks - DEBUG - Event needs-retry.iot-data-plane.Publish: calling handler 
2022-06-25 11:57:55,898 - MainThread - botocore.retryhandler - DEBUG - No retry needed.
2022-06-25 11:57:55,898 - MainThread - awscli.formatter - DEBUG - RequestId: 2740292f-48b4-3fca-2fe6-11f6bbfaf895
```

I have not tried this with boto3, but it might work if you specify an endpoint.

Unable to publish MQTT message to AWS iot Core with lambda function. Where lambda is connected to VPC. Using VPC enpoint we need to connect to IOT core and publish message

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