Trigger a lambda function based on thing type

Question

How do you i trigger a lambda function based on a thing type? For example add a rule whenever a device shadow was updated. My use case is, having two cloudformation stacks for dev and staging.  
All lambda functions are tagged specifically per stack. (Eg shadow-update-dev, shadow-update-staging). I'm thinking to add a attribute or type for a thing, and create an IOT rule to trigger what tag function it should trigger.  
  
Should i just create a placeholder lambda that checks the thing type and trigger whats the corresponding lambda function? Is a step function a good match for this?

Answer

I'm a little surprised the second approach didn't work. If the topic() function is not evaluated first before sending the value to Lambda, you can write this in a nested way to work around:

```
SELECT aws_lambda("arn:aws:lambda:eu-west-1:xxxx:function:xxxx", {"payload": topic}) as deviceEnv FROM (SELECT *, topic(3) as topic FROM 'device/test')
```

Admittedly I did not test the above SQL, but this is how I've solved past similar issues where values needed be generated and bubbled up to a secondary query.  
  
HTH,  
Ryan

Answer

Ive tried using the aws_lambda  
  
https://docs.aws.amazon.com/iot/latest/developerguide/iot-sql-functions.html#iot-func-aws-lambda  
  
It looks like the sql dont support passing topic vars?

```
SELECT topic(3) as id, aws_lambda("arn:aws:lambda:eu-west-1:xxxx:function:xxxx", {"payload": id}) as deviceEnv FROM 'device/test'
```

or

```
SELECT aws_lambda("arn:aws:lambda:eu-west-1:xxxx:function:xxxx", {"payload": topic(3)}) as deviceEnv FROM 'device/test'
```

Answer

It seems it wont work

Answer

Actually the second option worked. My mistake not updating the topic filter to

```
device/test/+
```

```
SELECT * FROM 'device/test/+' WHERE (SELECT aws_lambda("arn:aws:lambda:region:accountId:function:functionName", {"deviceId": topic(3)}).env as env FROM 'device/test/+') = "dev"
```

The where clause doesnt seem to work  
  
Edited by: janpoltan on Apr 3, 2019 1:44 AM

Answer

Moved to other post

Answer

Hi janpoltan,  
  
Today, the rules engine cannot fetch thing type, thing group, or registry attributes for a thing when processing a message. You could write a Lambda function to fetch these kinds of metadata and evaluate that at runtime with the aws_lambda() function: https://docs.aws.amazon.com/iot/latest/developerguide/iot-sql-functions.html#iot-func-aws-lambda   
  
The other way to achieve that is as you describe, with a Step Functions solution.  
  
A third way to achieve this, if it makes sense for your solution, is to store the thing type in the device shadow. The shadow can be referenced by the rules engine at runtime today. The main concern is whether this leaks inappropriate control plane info to your data plane, or whether there is risk of your device or other actors accidentally clearing this type from the shadow.   
  
Ryan

Trigger a lambda function based on thing type

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