AWS Lambda VPC on Terraform

I think the value of subnet_ids is like this: "subnet-xxxxx,subnet-yyyyy,subnet-zzzzz" and it take it as single subnet instead of list. You can fix this problem like this:

vpc_config {
  subnet_ids = ["${split(",", var.subnet_ids)}"]
  security_group_ids = ["${var.security_group_ids}"]
}

There was a mapping missing to the lambda module. After fixing it this how the plan should have looked like for the VPC configuration:

vpc_config.#:                              "1"
vpc_config.0.security_group_ids.#:         "1"
vpc_config.0.security_group_ids.571116572: "******"
vpc_config.0.subnet_ids.#:                 "3"
vpc_config.0.subnet_ids.1396457994:        "****"
vpc_config.0.subnet_ids.1722519307:        "****"
vpc_config.0.subnet_ids.830820656:         "****"
vpc_config.0.vpc_id:                       "<computed>"