Cross-Account Lambdas to API Gateway Setup - amazon-web-services

Question

So the scenario is we have 3 different accounts(EDGE, PROD, DEV). I want to create some APIs in EDGE account and integrate them with lambdas in DEV and PROD Account respectively.
I have 2 different stages of API : dev/prod and also have defined integration of API : LAMBDA with target = ${stageVariables.LAMBDA}.
When I mention the full ARN of LAMBDA in stage variables it shows the following error after api hit:
{
"message": "1 validation error detected: Value \'arn:aws:lambda:ap-south-1:XXEDGEACCOUNTXX:function:arn:aws:lambda:ap-south-1:XXDEVACCOUNTXX:function:funcName\' at \'functionName\' failed to satisfy constraint: Member must satisfy regular expression pattern: (arn:(aws[a-zA-Z-]*)?:lambda:)?([a-z]{2}((-gov)|(-iso(b?)))?-[a-z]+-\\d{1}:)?(\\d{12}:)?(function:)?([a-zA-Z0-9-_\\.]+)(:(\\$LATEST|[a-zA-Z0-9-_]+))?"
}
with
target = arn:aws:lambda:ap-south-1:${stageVariables.ACC}:function:${stageVariables.LAMBDA}/invocations
I get error of invalid function ARN or URI while saving it..
Please help.
PS. Permissions policy are attached perfectly fine. Issue is API gateway check Lambda in own account only that's why read only function name and keep account number fixed.

Answer 1

There is a mistake in the below statement
target = arn:aws:lambda:ap-south-1:${stageVariables.ACC}:function:${stageVariables.LAMBDA}/invocations
${stageVariables.LAMBDA} in the above statement is getting resolved to the lambda function arn. Hence there is a validation error.
arn:aws:lambda:ap-south-1:XXEDGEACCOUNTXX:function:arn:aws:lambda:ap-south-1:XXDEVACCOUNTXX:function:funcName
Also, noticed that the target arn your building is incorrect and should be of the below form
A stage variable can be used in place of a Lambda function name, or version/alias, as shown in the following examples.
arn:aws:apigateway:<region>:lambda:path/2015-03-31/functions/arn:aws:lambda:<region>:<account_id>:function:${stageVariables.<function_variable_name>}/invocations
arn:aws:apigateway:<region>:lambda:path/2015-03-31/functions/arn:aws:lambda:<region>:<account_id>:function:<function_name>:${stageVariables.<version_variable_name>}/invocations
For more information can go through this link
https://docs.aws.amazon.com/apigateway/latest/developerguide/aws-api-gateway-stage-variables-reference.html