Example infrastructure-live for Terragrunt

This repo, along with the terragrunt-infrastructure-modules-example
repo, show an example file/folder structure
you can use with Terragrunt to keep your
Terraform code DRY. For background information, check out the Keep your Terraform code
DRY section of the Terragrunt documentation.

This repo shows an example of how to use the modules from the terragrunt-infrastructure-modules-example repo to
deploy an Auto Scaling Group (ASG) and a MySQL DB across three environments (qa, stage, prod) and two AWS accounts
(non-prod, prod), all without duplicating any of the Terraform code. That's because there is just a single copy of
the Terraform code, defined in the terragrunt-infrastructure-modules-example repo, and in this repo, we solely define
terragrunt.hcl files that reference that code (at a specific version, too!) and fill in variables specific to each
environment.

Note: This code is solely for demonstration purposes. This is not production-ready code, so use at your own risk. If
you are interested in battle-tested, production-ready Terraform code, check out Gruntwork.

How do you deploy the infrastructure in this repo?

Pre-requisites

1. Install Terraform version 0.12.0 or newer and
   Terragrunt version v0.20.0 or newer.
2. Update the bucket parameter in non-prod/terragrunt.hcl and prod/terragrunt.hcl to unique names. We use S3
   as a Terraform backend to store your Terraform state, and
   S3 bucket names must be globally unique. The names currently in the file are already taken, so you'll have to
   specify your own. Alternatives, you can set the environment variable TG_BUCKET_PREFIX to set a custom prefix.
3. Configure your AWS credentials using one of the supported authentication
   mechanisms.

Deploying a single module

1. cd into the module's folder (e.g. cd non-prod/us-east-1/qa/mysql).
2. Note: if you're deploying the MySQL DB, you'll need to configure your DB password as an environment variable:
   export TF_VAR_master_password=(...).
3. Run terragrunt plan to see the changes you're about to apply.
4. If the plan looks good, run terragrunt apply.

Deploying all modules in a region

1. cd into the region folder (e.g. cd non-prod/us-east-1).
2. Configure the password for the MySQL DB as an environment variable: export TF_VAR_master_password=(...).
3. Run terragrunt plan-all to see all the changes you're about to apply.
4. If the plan looks good, run terragrunt apply-all.

Testing the infrastructure after it's deployed

After each module is finished deploying, it will write a bunch of outputs to the screen. For example, the ASG will
output something like the following:

Outputs:

asg_name = tf-asg-00343cdb2415e9d5f20cda6620
asg_security_group_id = sg-d27df1a3
elb_dns_name = webserver-example-prod-1234567890.us-east-1.elb.amazonaws.com
elb_security_group_id = sg-fe62ee8f
url = http://webserver-example-prod-1234567890.us-east-1.elb.amazonaws.com:80

A minute or two after the deployment finishes, and the servers in the ASG have passed their health checks, you should
be able to test the url output in your browser or with curl:

curl http://webserver-example-prod-1234567890.us-east-1.elb.amazonaws.com:80

Hello, World

Similarly, the MySQL module produces outputs that will look something like this:

Outputs:

arn = arn:aws:rds:us-east-1:1234567890:db:terraform-00d7a11c1e02cf617f80bbe301
db_name = mysql_prod
endpoint = terraform-1234567890.abcdefghijklmonp.us-east-1.rds.amazonaws.com:3306

You can use the endpoint and db_name outputs with any MySQL client:

mysql --host=terraform-1234567890.abcdefghijklmonp.us-east-1.rds.amazonaws.com:3306 --user=admin --password mysql_prod

How is the code in this repo organized?

The code in this repo uses the following folder hierarchy:

account
 └ _global
 └ region
    └ _global
    └ environment
       └ resource

Where:

• Account: At the top level are each of your AWS accounts, such as stage-account, prod-account, mgmt-account,
  etc. If you have everything deployed in a single AWS account, there will just be a single folder at the root (e.g.
  main-account).

• Region: Within each account, there will be one or more AWS
  regions, such as
  us-east-1, eu-west-1, and ap-southeast-2, where you've deployed resources. There may also be a _global
  folder that defines resources that are available across all the AWS regions in this account, such as IAM users,
  Route 53 hosted zones, and CloudTrail.

• Environment: Within each region, there will be one or more "environments", such as qa, stage, etc. Typically,
  an environment will correspond to a single AWS Virtual Private Cloud (VPC), which
  isolates that environment from everything else in that AWS account. There may also be a _global folder
  that defines resources that are available across all the environments in this AWS region, such as Route 53 A records,
  SNS topics, and ECR repos.

• Resource: Within each environment, you deploy all the resources for that environment, such as EC2 Instances, Auto
  Scaling Groups, ECS Clusters, Databases, Load Balancers, and so on. Note that the Terraform code for most of these
  resources lives in the terragrunt-infrastructure-modules-example repo.

Creating and using root (account) level variables

In the situation where you have multiple AWS accounts or regions, you often have to pass common variables down to each
of your modules. Rather than copy/pasting the same variables into each terragrunt.hcl file, in every region, and in
every environment, you can inherit them from the inputs defined in the root terragrunt.hcl file.