This Terraform script sets up a basic AWS infrastructure for a serverless application. The infrastructure includes a VPC with public and private subnets, an Internet Gateway, a NAT Gateway, an Amazon DocumentDB cluster, an API Gateway, and a Lambda function. The Lambda function interacts with the DocumentDB cluster, and the API Gateway provides a public interface to trigger the Lambda function.

Here is the design of the solution construct

• AWS CLI installed and configured
• Terraform CLI installed

• Configures the AWS provider for the eu-west-1 region.

provider "aws" {
  region = "eu-west-1"
}

• Defines a variable secret_id with a default value. This variable is used as the name for the DocumentDB cluster.

variable "secret_id" {
  type    = string
  default = "documentdbblogdemo"
}

• Creates a VPC with DNS support and hostnames enabled.

resource "aws_vpc" "vpc" {
  cidr_block           = "10.0.0.0/16"
  enable_dns_support   = true
  enable_dns_hostnames = true

  tags = {
    Name = "Otel-Serverless-Demo"
  }
}

• Creates an Internet Gateway and associates it with the VPC.

resource "aws_internet_gateway" "gw" {
  vpc_id = aws_vpc.vpc.id

  tags = {
    Name = "main"
  }
}

• Defines public and private subnets.

resource "aws_subnet" "public_subnet" {
  count             = 1
  ...
}

resource "aws_subnet" "private_subnet" {
  count             = 2
  ...
}

• Creates a NAT Gateway for private subnet communication.

resource "aws_nat_gateway" "nat_gateway" {
  ...
}

• Defines route tables for private subnets.

resource "aws_route_table" "private_route_table" {
  ...
}

• Creates an Amazon DocumentDB cluster.

resource "aws_docdb_cluster" "docdb_cluster" {
  ...
}

• Defines security groups for NAT Gateway and DocumentDB cluster.

resource "aws_security_group" "nat_sg" {
  ...
}

resource "aws_security_group" "docdb_sg" {
  ...
}

• Sets up a Lambda function with necessary IAM roles and policies.

resource "aws_lambda_function" "lambda_function" {
  ...
}

• Configures an API Gateway to trigger the Lambda function.

resource "aws_apigatewayv2_api" "http_api" {
  ...
}

• Defines IAM roles and policies for Lambda execution.

resource "aws_iam_role" "iam_for_lambda" {
  ...
}

resource "aws_iam_policy" "lambda_policy" {
  ...
}

• Sets up AWS Secrets Manager for storing secret information.

resource "aws_secretsmanager_secret" "docdb_secret" {
  ...
}

resource "aws_secretsmanager_secret_version" "docdb_secret_version" {
  ...
}

• Deploys the API Gateway.

resource "aws_apigatewayv2_deployment" "api_deployment" {
  ...
}

• Grants API Gateway permission to invoke the Lambda function.

resource "aws_lambda_permission" "lambda_permission" {
  ...
}

• Outputs the URL of the deployed API Gateway stage.

output "api_gateway_url" {
  ...
}

1. Make sure your AWS CLI is configured with the necessary credentials.
2. Install the Terraform CLI.
3. Run terraform init and terraform apply to create the infrastructure.

Remember to destroy the resources after usage by running terraform destroy to avoid unnecessary costs.