Invoke an AWS lambda across regions

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Thank you everyone for the input. @Michael-sqlbot's comment about the AWS client library defaulting to sending requests to the local region is what helped me find the solution. For Python, the library is boto3. Having read the docs it was not clear how to set the region. It was this blog post that provided the (simple) answer:

client = boto3.client('lambda', region_name='us-west-2')

You are right Michael that the use case for one lambda to another between regions is convoluted. I'll leave this answer here in case any others who are new to boto3 encounter the same error when trying to get other resources (lambda to ec2, lambda to s3, etc) to work across regions.
Thanks

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Sawyer Merchant
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Updated on June 04, 2022

Comments

  • Sawyer Merchant
    Sawyer Merchant over 1 year

    I have three lambda functions: boss, worker1, worker2. When using boto3.client.invoke I am able to call worker1 from boss. These two are in the same region.
    worker2 is in a separate region. When attempting to call worker2 from boss the following error returns:
    "An error occurred (ResourceNotFoundException) when calling the Invoke operation: Functions from 'us-east-1' are not reachable in this region ('us-west-2')" . boss has an execution role with the following permission:

    {
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": [
                "lambda:InvokeFunction"
            ],
            "Effect": "Allow",
            "Resource": "arn:aws:lambda:*:*:*"
        }
    ]
    }
    

    Please help clarify how permissions need to be conveyed for this to work. Thanks

    Edit: master and worker1 are in us-west-2 and worker1 is in us-east-1.
    Here is the code used to invoke worker from master:

    def lambda_handler(event, context):
    function_name = "arn:aws:lambda:us-east-1-...:function:worker_2"
    lambda_client = boto3.client('lambda')
    payload = json.dumps({"body-json": "payload string")
    response = lambda_client.invoke(
        FunctionName = function_name,
        Payload = payload
    )
    response_payload = response['Payload'].read()
    response_arr = json.loads(response_payload)
    return response_arr['answer']
    
    • Dunedan
      Dunedan almost 6 years
      Please share the code you use to invoke the functions as well.
  • Michael - sqlbot
    Michael - sqlbot almost 6 years
    The point of the question seems to be that worker2, for whatever reason but presumably intentionally, is in us-east-1, a different region from the others. All that's needed is to tell boto3 to send the request to the Lambda service API in us-east-1 and use us-east-1 in the Sig V4 credential. The permissions are already present, as shown. Adding API Gateway to solve a simple problem seems like an unnecessary convolution.
  • Joe Atzberger
    Joe Atzberger over 2 years
    This is super helpful on your part and very painfully unhelpful on boto's part. The local region is used even when the full ARN including region is supplied, like client.invoke(FunctionName='arn:aws:lambda:us-east-1:1234555‌​55555:function:worke‌​r'). That seems bizarre.