My Journey into Terraform: Part 1

The D2SI Technical Blog

By Gauthier Wallet - @Ninnir, 08 Apr 2017


At D2SI we truly believe in automating IT infrastructures. As a DevOps working for a company that promotes automation, one of your main objectives is to keep seeking the right tools and sometimes bet on them. Terraform, among many others, is one of them.

Terraform is an open-source tool for building, modifying and versioning infrastructure safely and efficiently. It helps ops (OPerationS) benefit from a concept called IaC (Infrastructure as code) for describing infrastructures based on a declarative language called HCL (HashiCorp Configuration Language). Here is an example that will be interpreted into an API call creating an AWS instance (aka virtual machine) of type t2.nano (500MB RAM, 1vCPU) and based on the AMI ID ami-e5083683 (Amazon Linux 2017.03.0):

resource "aws_instance" "example" {
  ami           = "ami-e5083683"
  instance_type = "t2.nano"

Using the command-line tool, you can then interact with this configuration and apply your changes. The journey can now begin!

Getting deeper

With a developer background and currently working as an ops (yeah you got it, “DevOps”), it brings me the logic and flexibility I need to build infrastructures for my clients like provisioning an entire VPC (Virtual Private Cloud), managing load balancers, databases, deploying serverless applications, etc.

A few months ago, I was working on a project that was processing raw data to structured one for display purposes. We needed to deliver notification messages to a WebApp using a password-protected HTTPS endpoint that looked like this:

The tool used for this is called SNS: Simple Notification Service. It is an AWS managed service allowing users to send notifications to multiple endpoints using a defined protocol: email, HTTP, SMS, etc. To proceed, users first need to create a topic and then add subscriptions (that must be acknowledged). If we were to use the AWS cli, it would look like:

aws sns subscribe --topic-arn arn:aws:sns:eu-west-1:123456789098:my-topic --protocol http --notification-endpoint

This would create a subscription for the endpoint, linked to the arn:aws:sns:eu-west-1:123456789098:my-topic topic using the http protocol.

The documentation explicitly states that the endpoint has to auto-confirm the unique URL that is sent by AWS, by making a call to it. However, even though the confirmation was made on the AWS side and the console successfully exposed it, the Terraform abstraction was not aware of it, resulting in a timeout.

Fixing the matrix

I then realized that fixing this bug would be the perfect opportunity for me to contribute to the Terraform project. So I started looking at the code and learning the Go programming language which ended up being a double win for me. Slowly getting into the codebase, I started documenting my findings and exploring what was already being worked on in the various pull requests.

Once I gained enough confidence and in order to find that bug, I got through the process of developping Terraform. Being all set-up, I started my debugging session:

TF_LOG=DEBUG TF_LOG_PATH=terraform.log terraform apply

Here are a few hints on what is done:

Taking our previous example, i.e., I found out that the endpoint returned by AWS when subscribing contained an obfuscated string, replacing the password field. What it means is that when I sent:

I got this in return:


This led me to the bug: it was comparing the sent value (my endpoint) with the returned one (obfuscated), which would obviously always return false. So I created a small function reproducing the obfuscation using Go:

// returns the endpoint with obfuscated password, if any
func obfuscateEndpointPassword(endpoint string) string {
	r := regexp.MustCompile("(://[^:]+):([^@]+)")
	return r.ReplaceAllString(endpoint, fmt.Sprintf("$1:%s", awsSNSPasswordObfuscationPattern))

This simple code block will translate any URL into its corresponding obfuscated version, as in:

URL Obfuscated version
“” “”
“” “”
“” “https://username:**”

With the code written & unit tests passing, I fixed the buggy instruction and threw my first contribution to Terraform. All the work resides on GitHub and should be merged soon!

Journey ain’t over

As a developer, I have to admit I fell in love with Go and the Terraform API. This work was the first experience I had with the Terraform codebase and, under the D2SI flag, I have since contributed many documentation fixes, multiple new resources, fixed dozens of bugs and helped people. The journey into Terraform just started, stay tuned for the next episode!