# Terraform template to have VPC flow logs be sent to AWS Lambda

provider "aws" {
  region = "us-west-2"
}

resource "aws_cloudwatch_log_group" "vpc_flow_log_group" {
  name = "vpc-flow-log-group"
  retention_in_days = 1
}

resource "aws_flow_log" "vpc_flow_log" {
  # log_group_name needs to exist before hand
  # until we have a CloudWatch Log Group Resource
  log_group_name = "${aws_cloudwatch_log_group.vpc_flow_log_group.name}"
  iam_role_arn = "${aws_iam_role.vpc_flow_logs_role.arn}"
  vpc_id = "vpc-XXXXXXXXX"
  traffic_type = "ALL"
}

resource "aws_iam_role" "vpc_flow_logs_role" {
  name = "vpc_flow_logs_role"
  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" "vpc_flow_logs_policy" {
  name = "vpc_flow_logs_policy"
  role = "${aws_iam_role.vpc_flow_logs_role.id}"
  policy = <<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "logs:CreateLogGroup",
        "logs:CreateLogStream",
        "logs:PutLogEvents",
        "logs:DescribeLogGroups",
        "logs:DescribeLogStreams"
      ],
      "Effect": "Allow",
      "Resource": "*"
    }
  ]
}
EOF
}

resource "aws_iam_role" "cloudwatch_lambda_role" {
  name = "cloudwatch_lambda_role"
  assume_role_policy = <<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": "sts:AssumeRole",
      "Principal": {
        "Service": "lambda.amazonaws.com"
      },
      "Effect": "Allow"
    }
  ]
}
EOF
}

resource "aws_iam_role_policy" "cloudwatch_lambda_policy" {
  name = "cloudwatch_lambda_policy"
  role = "${aws_iam_role.cloudwatch_lambda_role.id}"
  policy = <<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "AWSLambdaCloudwatchPolicy",
      "Effect": "Allow",
      "Action": [
        "logs:CreateLogStream",
        "logs:PutLogEvents",
        "ec2:DescribeNetworkInterfaces",
        "ec2:DeleteNetworkInterface",
        "ec2:CreateNetworkInterface"
      ],
      "Resource": "*"
    }
  ]
}
EOF
}

resource "aws_lambda_function" "flowlogs" {
    s3_key = "XXXXXXXXXX"
    function_name = "flowlogs"
    role = "${aws_iam_role.cloudwatch_lambda_role.arn}"
    handler = "XXXXXXXX"
    s3_bucket = "XXXXXXX"
    runtime = "java8"
    vpc_config {
    	subnet_ids = [ "subnet-XXXXXX" ]
    	security_group_ids = [ "sg-XXXXXX" ]
   	}
}

resource "aws_lambda_permission" "flowlog_permission" {
  statement_id = "vpc_flow_log_activation"
  action = "lambda:InvokeFunction"
  function_name = "${aws_lambda_function.flowlogs.arn}"
  principal = "logs.us-east-1.amazonaws.com"
  source_arn = "${aws_cloudwatch_log_group.vpc_flow_log_group.arn}"
}

resource "aws_cloudwatch_log_subscription_filter" "flowlog_subscription_filter" {
  depends_on = ["aws_lambda_permission.flowlog_permission"]
  name = "cloudwatch_flowlog_lambda_subscription"
  log_group_name = "${aws_cloudwatch_log_group.vpc_flow_log_group.name}"
  filter_pattern = ""
  destination_arn = "${aws_lambda_function.flowlogs.arn}"
}