This project is part of one big project where I research how to build infrastructure in AWS for 2-tier application (and application as well, of course) :

1. Terraform (this project) contains all the terraform code to deploy required infra & application code
2. Simple Web GUI contains code for simple Web GUI to bridge the gap between user and Lambda functions
3. Lambda functions contain code for 3 Lambda functions that replicate simple backend functions
   1. return_ip - returns IP address of the Lambda function
   2. fetch_go_versions - returns JSON with recent 5 Go versions
   3. custom_auth - custom Lambda authorizer (only supports payload format version 1.0) that controls access to functions 1 & 2 when calling via API Gateway
   4. custom_auth_v2 - custom Lambda authorizer (only supports payload format version 2.0) that controls access to functions 1 & 2 when calling via API Gateway

Simple representation of the thing that gets built with this Terraform project (application is also getting deployed as part of this Terraform project):

                   ------------------------------------|--------------------------------
                   |                MAIN VPC           |            Public space       |
                   |                                   |                               |
                   |                                   |            <-->  Auth Lambda  |
              -----------                       ---------------     |                  |
Client --->   | Route 53 |   --> Web GUI -->    | API Gateway | -->  -->  Lambda 1     |
              ------------                      ---------------     |                  |
                   |                                   |             -->  Lambda 2     |
                   |                                   |                               |
                   |                                   |                               |
                   ------------------------------------|--------------------------------

Auth(authentication) Lambda is required so we can delegate authentication to API Gateway (albeit there are other ways to do this) instead of doing it in Lambda 1/2

1. Git clone this project
2. Ensure you have authentication credentials set for Terraform; account should have permissions to create:
   1. Networks: VPC, Subnets, LB etc
   2. Applications: Auto Scaling groups, Launch templates etc
   3. API Gateway
   4. AWS Lambda Functions
3. Ensure you have following items ready prior to launching Terraform:
   1. S3 buckets to host Terraform state files for
      1. Networking - sets up network that would be used by API Gateway, Lambdas & Web Tier; set in network/backend-config.tfvars
      2. Lambdas - spins up Lambda Functions that are to be called from Web Tier (via API Gateway); set in lambdas/backend-config.tfvars
      3. API Gateway - sets up API Gateway: linkage between Web-Tier and Lambdas + authentication; set in api-gateway/backend-config.tfvars & api-gateway/data.tf >> data >> config >> bucket & region (same as what set in network)
      4. Web Tier - sets up servers hosted in public subnets; accessible via Internet; set in web-tier/backend-config.tfvars & web-tier/data.tf >> data >> config >> bucket & region (same as what set in network & api-gateway)
      5. Route53 - links custom DNS (with HTTPS cert) to Web Tier LB; set in route53/backend-config.tfvars & route53/data.tf >> data >> config >> bucket & region (same as what set in web-tier)
   2. terraform.tfvars file in each of the module: api-gateway, lambdas, network, route53, web-tier to specify:
      1. TLS certificates (specifically ARN of those) - these would be used to ensure HTTPS connectivity is properly handled
      2. SSH Keys - so you would be able to log onto Web Tier servers in case you need to debug/play around with those
      3. There are other required variables, please refer to variables.tf in each module
   3. backend-config.tfvars file in each of the module: api-gateway, lambdas, network, route53, web-tier to specify:
      1. bucket - backend bucket
      2. key - backend key
      3. region - backend region
4. Items should be deployed in the following order:
   1. network - creates all network related resources

   # Required only once or whenever backend config changes
   terraform init -backend-config=backend-config.tfvars
   
   terraform plan  -var-file=terraform.tfvars -var-file=backend-config.tfvars
   terraform apply -var-file=terraform.tfvars -var-file=backend-config.tfvars -auto-approve
   

   2. lambdas - creates all required AWS Lambda Functions

   # Required only once or whenever backend config changes
   terraform init -backend-config=backend-config.tfvars
   
   terraform plan  -var-file=terraform.tfvars -var-file=backend-config.tfvars
   terraform apply -var-file=terraform.tfvars -var-file=backend-config.tfvars -auto-approve
   

   3. api-gateway - creates all AppTier (backend) related resources; depends on the output of network

   # Required only once or whenever backend config changes
   terraform init -backend-config=backend-config.tfvars
   
   terraform plan  -var-file=terraform.tfvars -var-file=backend-config.tfvars
   terraform apply -var-file=terraform.tfvars -var-file=backend-config.tfvars -auto-approve
   

   4. web-tier - creates all WebTier (front end) related resources; depends on the output of network & app-tier

   # Required only once or whenever backend config changes
   terraform init -backend-config=backend-config.tfvars
   
   terraform plan  -var-file=terraform.tfvars -var-file=backend-config.tfvars
   terraform apply -var-file=terraform.tfvars -var-file=backend-config.tfvars -auto-approve
   

   5. route53 - links custom DNS (with HTTPS cert) to Web Tier LB; depends on the output of web-tier

   # Required only once or whenever backend config changes
   terraform init -backend-config=backend-config.tfvars
   
   terraform plan  -var-file=terraform.tfvars -var-file=backend-config.tfvars
   terraform apply -var-file=terraform.tfvars -var-file=backend-config.tfvars -auto-approve
   

By default, AWS provider expects default AWS Config & Crendentials (this could be changed)

# from main.tf
provider "aws" {
  region  = "eu-west-2"
  profile = "default"
}

# cat ~/.aws/config
[default]
region = eu-west-2
output = json

# cat ~/.aws/credentials
[default]
aws_access_key_id     = <ACCESS_KEY_ID>
aws_secret_access_key = <SECRET_ACCESS_KEY>

1. At the moment it is not nicely implemented, so the only way to remove created infrastructure, is to

1. Comment out everything in main.tf & outputs.tf(if exists) for each deployed module
2. Run `terraform apply` in the following order (effectively in the reverse)
    1. Route53
    2. Web Tier
    3. API Gateway
    4. Lambdas
    5. Networks

1. Tested with Terraform v1.4.0