sample for aws iot publishing with apex.
AWSIoTClient client = new AWSIoTClient(
'input your aws access key id',
'input your aws secret access key',
'input your region',
'input your iot endpoint prefix'
);
String response = client.publish(
'input your topic name',
new Map<String, Object>{
'payload_key1' => 'payload_value1',
'payload_key2' => 'payload_value2'
}
);