terraform.aws-baseline-infra/modules/networking/vpc-subnet-manual/vpc-flowlog.tf

resource "aws_flow_log" "vpc-flowlog" {
  count           = var.enable-flow-log ? 1 : 0
  iam_role_arn    = aws_iam_role.vpcflowlog-role.arn
  log_destination = aws_cloudwatch_log_group.vpcflowlog-loggroup[0].arn
  traffic_type    = "ALL"
  vpc_id          = aws_vpc.vpc.id
  tags = {
    Name = "${var.resource-prefix}-vpcflowlog"
  }
}

resource "aws_cloudwatch_log_group" "vpcflowlog-loggroup" {
  count = var.enable-flow-log ? 1 : 0

  name_prefix = "vpcflowlog/${aws_vpc.vpc.id}/"
  kms_key_id  = var.vpcflowlog-cwl-loggroup-key-arn

  retention_in_days = var.vpcflowlog-retain-days
}

resource "random_id" "rid" {
  byte_length = 2
}

resource "aws_iam_role" "vpcflowlog-role" {
  name               = "VpcFlowlogRole-${random_id.rid.dec}"
  path               = "/service/"
  assume_role_policy = <<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "",
      "Effect": "Allow",
      "Principal": {
        "Service": "vpc-flow-logs.amazonaws.com"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}
EOF
}

resource "aws_iam_role_policy" "vpcflowlog-role-policy" {
  name = "VpcFlowlogRole-${random_id.rid.dec}"
  role = aws_iam_role.vpcflowlog-role.id

  policy = <<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "logs:CreateLogGroup",
        "logs:CreateLogStream",
        "logs:PutLogEvents",
        "logs:DescribeLogGroups",
        "logs:DescribeLogStreams"
      ],
      "Effect": "Allow",
      "Resource": "*"
    }
  ]
}
EOF
}