[SOLVED] Is it a possible to call a lambda in different account from the cloudformation one?

Is it a possible to call a lambda in different account from the cloudformation one?

I have a lambda on one account with this policy attached:

{
  "Sid": "Id-123",
  "Effect": "Allow",
  "Principal": { "AWS": "arn:aws:iam::115333656057:root"},
  "Action": "lambda:InvokeFunction",
  "Resource": "arn:aws:lambda:eu-central-1:260143830488:function:CentralInstanceScheduler-InstanceSchedulerMain"
}

When I create a stack from account 115333656057 with my user trying to execute the lambda I got this error:

  User: arn:aws:iam::115333656057:user/uguesm is not authorized to perform: lambda:InvokeFunction on resource: arn:aws:lambda:eu-central-1:260143830488:function:CentralizedInstanceScheduler-InstanceSchedulerMain

What am I doing wrong?

Solution

In Account 260143830488 - Edit your Role to add the policy to InvokeFunction and a trust policy for another account.

Permissions:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "lambda:InvokeFunction",
      "Resource": "arn:aws:lambda:eu-central-1:260143830488:function:CentralInstanceScheduler-InstanceSchedulerMain"
    },
  ]
}

Trust Relationship Policy:

{
  "Sid": "Id-123",
  "Effect": "Allow",
  "Principal": { "AWS": "arn:aws:iam::115333656057:role/<lambda-role>"},
  "Action": "sts:AssumeRole",
}

In Account 115333656057 - Create a lambda execution role to AssumeRole

Permissions:

{
  "Version": "2012-10-17",
  "Statement": {
    "Effect": "Allow",
    "Action": "sts:AssumeRole",
    "Resource": "arn:aws:iam::260143830488:role/<RoleName>"
  }
}

Trust Relationship policy:

{
  "Version": "2012-10-17",
  "Statement": {
    "Effect": "Allow",
    "Principal": {"Service": "lambda.amazonaws.com"},
    "Action": "sts:AssumeRole"
  }
}