Build a Terraform Module

Step-01: Introduction

Build a Terraform Module
- Create a Terraform module
- Use local Terraform modules in your configuration
- Configure modules with variables
- Use module outputs
- We are going to write a local re-usable module for the following usecase.
Usecase: Hosting a static website with AWS S3 buckets
Create an S3 Bucket
Create Public Read policy for the bucket
Once above two are ready, we can deploy Static Content
For steps, 1 and 2 we are going to create a re-usable module in Terraform
How are we going to do this?
We are going to do this in 3 sections
Section-1 - Full Manual: Create Static Website on S3 using AWS Management Consoleand host static content and test
Section-2 - Terraform Resources: Automate section-1 using Terraform Resources
Section-3 - Terraform Modules: Create a re-usable module for hosting static website by referencing section-2 terraform configuration files.

Step-02: Hosting a Static Website with AWS S3 using AWS Management Console

Reference Sub-folder: v1-create-static-website-on-s3-using-aws-mgmt-console
We are going to host a static website with AWS S3 using AWS Management console

Step-02-01: Create AWS S3 Bucket

Go to AWS Services -> S3 -> Create Bucket
Bucket Name: mybucket-1045 (Note: Bucket name should be unique across AWS)
Region: US.East (N.Virginia)
Rest all leave to defaults
Click on Create Bucket

Step-02-02: Enable Static website hosting

Go to AWS Services -> S3 -> Buckets -> mybucket-1045 -> Properties Tab -> At the end
Edit to enable Static website hosting
Static website hosting: enable
Index document: index.html
Click on Save Changes

Step-02-03: Remove Block public access (bucket settings)

Go to AWS Services -> S3 -> Buckets -> mybucket-1045 -> Permissions Tab
Edit Block public access (bucket settings)
Uncheck Block all public access
Click on Save Changes
Provide text confirm and Click on Confirm

Step-02-04: Add Bucket policy for public read by bucket owners

Update your bucket name in the below listed policy
Location: v1-create-static-website-on-s3-using-aws-mgmt-console/policy-public-read-access-for-website.json

{
  "Version": "2012-10-17",
  "Statement": [
      {
          "Sid": "PublicReadGetObject",
          "Effect": "Allow",
          "Principal": "*",
          "Action": [
              "s3:GetObject"
          ],
          "Resource": [
              "arn:aws:s3:::mybucket-1045/*"
          ]
      }
  ]
}

Go to AWS Services -> S3 -> Buckets -> mybucket-1045 -> Permissions Tab
Edit -> Bucket policy -> Copy paste the policy above with your bucket name
Click on Save Changes

Step-02-05: Upload index.html

Location: v1-create-static-website-on-s3-using-aws-mgmt-console/index.html
Go to AWS Services -> S3 -> Buckets -> mybucket-1045 -> Objects Tab
Upload index.html

Step-02-06: Access Static Website using S3 Website Endpoint

Access the newly uploaded index.html to S3 bucket using browser

# Endpoint Format
http://example-bucket.s3-website.Region.amazonaws.com/

# Replace Values (Bucket Name, Region)
http://mybucket-1045.s3-website.us-east-1.amazonaws.com/

Step-02-07: Conclusion

We have used multiple manual steps to host a static website on AWS
Now all the above manual steps automate using Terraform in next step

Step-03: Create Terraform Configuration to Host a Static Website on AWS S3

Reference Sub-folder: v2-host-static-website-on-s3-using-terraform-manifests
We are going to host a static website on AWS S3 using general terraform configuration files

Step-03-01: Create Terraform Configuration Files step by step

versions.tf
main.tf
variables.tf
outputs.tf
terraform.tfvars

Step-03-02: Execute Terraform Commands & Verify the bucket

# Terraform Initialize
terraform init

# Terraform Validate
terraform validate

# Terraform Format
terraform fmt

# Terraform Plan
terraform plan

# Terraform Apply
terraform apply -auto-approve

# Verify 
1. Bucket has static website hosting enabled
2. Bucket has public read access enabled using policy
3. Bucket has "Block all public access" unchecked

Step-03-03: Upload index.html and test

# Endpoint Format
http://example-bucket.s3-website.Region.amazonaws.com/

# Replace Values (Bucket Name, Region)
http://mybucket-1046.s3-website.us-east-1.amazonaws.com/

Step-03-04: Destroy and Clean-Up

# Terraform Destroy
terraform destroy -auto-approve

# Delete Terraform files 
rm -rf .terraform*
rm -rf terraform.tfstate*

Step-03-05: Conclusion

Using above terraform configurations we have hosted a static website in AWS S3 in seconds.
In next step, we will convert these terraform configuration files to a Module which will be re-usable just by calling it.

Step-04: Build a Terraform Module to Host a Static Website on AWS S3

Reference Sub-folder: v3-build-a-module-to-host-static-website-on-aws-s3
We will build a Terraform module to host a static website on AWS S3

Step-04-01: Create Module Folder Structure

We are going to create modules folder and in that we are going to create a module named aws-s3-static-website-bucket
We will copy required files from previous section for this respective module.
Terraform Working Directory: v3-build-a-module-to-host-static-website-on-aws-s3
- modules
  - Module-1: aws-s3-static-website-bucket
    - main.tf
    - variables.tf
    - outputs.tf
    - README.md
    - LICENSE
Inside modules/aws-s3-static-website-bucket, copy below listed three files from v2-host-static-website-on-s3-using-terraform-manifests
- main.tf
- variables.tf
- outputs.tf

Step-04-02: Call Module from Terraform Work Directory (Root Module)

Create Terraform Configuration in Root Module by calling the newly created module
c1-versions.tf
c2-variables.tf
c3-s3bucket.tf
c4-outputs.tf

module "website_s3_bucket" {
  source = "./modules/aws-s3-static-website-bucket"
  bucket_name = var.my_s3_bucket
  tags = var.my_s3_tags
}

Step-04-03: Execute Terraform Commands

# Terraform Initialize
terraform init
Observation: 
1. Verify ".terraform", you will find "modules" folder in addition to "providers" folder
2. Verify inside ".terraform/modules" folder too.

# Terraform Validate
terraform validate

# Terraform Format
terraform fmt

# Terraform Plan
terraform plan

# Terraform Apply
terraform apply -auto-approve

# Verify 
1. Bucket has static website hosting enabled
2. Bucket has public read access enabled using policy
3. Bucket has "Block all public access" unchecked

Step-04-04: Upload index.html and test

# Endpoint Format
http://example-bucket.s3-website.Region.amazonaws.com/

# Replace Values (Bucket Name, Region)
http://mybucket-1047.s3-website.us-east-1.amazonaws.com/

Step-04-05: Destroy and Clean-Up

# Terraform Destroy
terraform destroy -auto-approve

# Delete Terraform files 
rm -rf .terraform*
rm -rf terraform.tfstate*

Step-04-06: Understand terraform get command

We have used terraform init to download providers from terraform registry and at the same time to download modules present in local modules folder in terraform working directory.
Assuming we already have initialized using terraform init and later we have created module configs, we can terraform get to download the same.
Whenever you add a new module to a configuration, Terraform must install the module before it can be used.
Both the terraform get and terraform init commands will install and update modules.
The terraform init command will also initialize backends and install plugins.

# Delete modules in .terraform folder
ls -lrt .terraform/modules
rm -rf .terraform/modules
ls -lrt .terraform/modules

# Terraform Get
terraform get
ls -lrt .terraform/modules

Step-04-07: Major difference between Local and Remote Module

When installing a remote module, Terraform will download it into the .terraform directory in your configuration's root directory.
When installing a local module, Terraform will instead refer directly to the source directory.
Because of this, Terraform will automatically notice changes to local modules without having to re-run terraform init or terraform get.

Step-05: Conclusion

Created a Terraform module
Used local Terraform modules in your configuration
Configured modules with variables
Used module outputs