REFACTOR.md

Terratest refactor

Terratest started out as a set of Bash scripts we were using at Gruntwork to test some of our Terraform code. As the amount of Terraform code grew, it was getting trickier and trickier to test it with Bash, so we rewrote those scripts in Go. Over time, this Go code grew into a library called Terratest, which contains collection of utilities that we use to test all aspects of our Infrastructure as Code Library.

We developed patterns to test Terraform configurations, Packer templates, Docker images, SSH access, AWS APIs, shell commands, and much more. We built this library because we couldn't find any existing tools out there that could do the type of real-world testing we needed. It turns out many other companies want to do this type of testing too, so now it's time to open source Terratest.

This library grew organically, so it needs lots of refactoring, cleanup, and documentation to be useful to people outside of Gruntwork. This document lays out the refactoring we are planning to (a) get feedback and (b) document what changed so that when we update our code, we know how to deal with the backwards incompatibilities.

Name change

"Terratest" made sense as the name for this library when it was all about testing Terraform code, but now this library also can help you test Packer templates, Docker images, and much more. I propose that we rename it. Some ideas:

• grunt-test
• test-grunt
• gruntUnit
• iac-test
• infratest

Build updates

1. Move from Glide to Dep
2. Move from CircleCI 1.0 to 2.0
3. Add support for Google Cloud Platform
4. Move from Dep to Go Modules.

Folder structure

Change to the same folder structure we use for just about all other Gruntwork repos:

• examples: This will contain a number of real-world examples of code you might want to test with Terratest, such as Terraform modules, Packer templates, and Docker images. The test folder (described below) shows how to use Terratest to test these examples.

• modules: The Terratest source code. Move all the .go files and packages into this folder so it's easier to browse the repo. That does mean all Terratest imports will have to be updated to github.com/gruntwork-io/terratest/modules/xxx. Unit tests for the Go source code will be in this folder too (e.g., the unit test for foo.go will be in foo_test.go).

• test: This will contain the automated tests for the examples in the examples folder. These will act both as an example of how to use Terratest, as well as integration tests for the library.

Documentation

Update the root README.md with documentation that shows how to use Terratest:

• Overview of what Terratest is.
• Link to blog post we'll write about Terratest (this blog post is a TODO for after this refactor).
• Discuss some of the challenges of testing infrastructure code: i.e., lack of "localhost," lock of "unit tests," slowness, brittleness.
• Discuss the value of doing this testing despite the challenges: i.e., there is no way to maintain lots of infrastructure code without tests, building reusable, tested, versioned modules changes how you manage infrastructure.
• Discussion of test strategies: using Docker for local testing, test stages, retries, mocks, small modules, test pyramid, cleanup, cloud-nuke.
• Point to examples folder for real-world code you may want to test and test folder for examples of how to use Terratest to test that code.
• Overview of Terratest packages. Explain what each top-level package in Terratest does. We can't do a method-by-method breakdown, as that would go out of date immediately, so instead, link to the appropriate examples subfolder that shows real-world usage of that package.
• In the future: links to our open source repos (Vault, Consul, Nomad, Couchbase, etc) that show how we use Terratest with our own code. We can't add this until we update those open source repos to this refactored version of Terratest so the code matches up.

Package-by-package refactor

I've gone through each of the packages in Terratest and took down some notes on cleanup we need to do. This is not a comprehensive list, as things will become clearer once I actually start doing the work.

In fact, my plan is to first create all the examples in the examples folder, then write tests for them in the test folder using "wishful thinking" (in the SICP sense), where I come up with the test API I want to have for doing the testing, and then go and refactor the Terratest code to match.

Root package

We have a lot of stuff in the root package and I propose moving all of it out into appropriate sub-packages:

• apply.go, apply_and_destroy.go, destroy.go, output.go, and output_test.go will all be moved into modules/terraform, as they are all specific to testing Terraform code.

• I propose deleting rand_resources.go and rand_resource_test.go and extracting its logic into other places. The RandomResourceCollection ended up being a, well, random collection of resources, most of which don't apply to most of our tests, and certainly won't apply to tests written by the open source community. Here's what RandomResourceCollection contains and what I propose to do with it:

  • UniqueId: We already have a separate method for generating a unique ID and we can pass it around as a string.

  • AwsRegion: This is only needed for AWS tests. We want to expand Terratest to support other clouds, so it needs to be separated anyway. Code that needs an AWS region should call a method in the modules/aws package to pick a random AWS region (passing in a list of forbidden regions, if necessary) and can pass that around as a string.

  • KeyPair: This is only needed for a small percentage of our AWS tests that deploy EC2 Instances and SSH to them. Those tests should call a standalone method in the modules/aws package to generate this KeyPair when they need it, instead of us assuming every single test needs it.

  • AmiId: We used to look up vanilla Ubuntu or Amazon Linux AMI IDs and put them in this field, but now that Terraform has data sources and Packer has source_ami_filter, this is no longer necessary. We can keep the methods around to find Ubuntu or Amazon Linux AMI IDs for tests that need them, but there's no need to assume every single test needs this.

  • AccountId: Our Terraform examples used to require an account ID to be passed in. We now avoid this to make the examples easier to use, and fetch it automatically using Terraform's aws_caller_identity data source if it's absolutely necessary. Code that needs an account ID should call a method in the modules/aws package to fetch it, but we shouldn't assume every single test needs it.

  • SnsTopicArn: A very, very small percentage of our tests needed an SNS topic passed in. Those tests should call a method in the modules/aws package to create this topic instead of us assuming every single test needs it.

• I propose moving terratest_options.go to modules/terraform/options.go and renaming the struct within it from TerratestOptions to Options, since this is solely used for testing Terraform code. We should also rename TemplatePath to TerraformDir, as .tf files are technically called "configurations" and not "templates".

• url_checker.go will be deleted. It's too hard-coded for one specific type of check. The reuse value is limited and it's not obvious the code exists, so it's best for the test cases to reimplement this themselves, with their specific needs, even if it's a tiny bit less DRY.

_docker-images package

• Rename to test-docker-images to make it clearer these are only used for testing.
• Use these Docker images in the examples folder to show how to do "unit tests" for Packer templates.
• Follow-up PR: build and push a new version of these Docker images on each release?
• Follow-up PR: tag each new Docker image with a unique version number (e.g., sha1 of commit).

aws package

• Right now, much of this code has no unit tests, since it relies on resources in AWS. By adding an examples folder that deploys real resources in AWS, we will be able to test this code better, and show users how to use this code!

• ami.go: Update these methods to use the AWS APIs to find the latest Ubuntu / Amazon Linux AMI IDs instead of hard-coding them.

• kms.go: What to do about GetDedicatedTestKeyArn? For tests that use KMS, we don't want to create a new CMK each time the test runs, as AWS charges $1/month for CMKs, even if you delete them immediately after use. This method currently assumes we have a key called alias/dedicated-test-key in every AWS region. Should we leave it as-is and document it for Terratest users that want to follow a similar pattern? Or perhaps read the key name from an env var?

• region.go: What should we do about GetGloballyForbiddenRegions? Right now, it's hard-coded to include us-west-2 as a globally forbidden region, as Josh is running his personal blog there. Obviously, we don't want that in the open source version. Josh, can you finally migrate your blog out of there so we don't have to have this exception?

log package

• Rename to logger. That way, we don't have to alias it as terralog all over our test code.
• Change what the package does. Instead of creating a custom *log.Logger and passing it around, we are going to have a Log and Logf method you can call from anywhere. To use those methods, you have to pass them a *testing.T, which they will use to read out the test name. We already pass *testing.T to almost all of our test methods, so this reduces the number of arguments by one.

parallel package

• I propose removing this package entirely. Now that go has subtests that you can easily run with t.Run() and parallelize with t.Parallel(), I think that's a cleaner way of handling parallelism than this custom package.

packer package

• Rename PackerOptions to Options (the package name is already packer).

resources package

• base_resources.go is no longer necessary if we remove RandomResourceCollection.
• exclusions.go is not used much and very out of date.
• terraform_options.go is hard-coded to how we do things at Gruntwork, but won't apply to many other users.

terraform package

• apply.go: Remove terraformDebugEnv and instead make it easy to pass a map of env vars to the Apply method. Refactor ApplyAndGetOutputWithRetry to accept a list of errors on which to retry and how many retries to do.

test-util package

• dummy_server.go: Move into the modules/http package.
• Remove test-util since that would leave it empty!

util package

• collections.go: Move into its own modules/collections package.
• keygen.go: Move into modules/ssh package.
• network.go: Move into modules/aws package.
• sleep.go: Remove. Didn't even know we had this and doubt it gets much use!
• random.go: Move into its own modules/random package.
• retry.go: Move into its own modules/retry package.

Error handling

I am updating most of the methods to support handling errors in one of two ways:

1. Each method foo will take in a *testing.T and upon hitting an error, call t.Fatal.
2. Each method fooE will explicitly return any errors it hits and NOT call t.Fatal.

Example:

func GetCurrentBranchName(t *testing.T) string {
	out, err := GetCurrentBranchNameE(t)
	if err != nil {
		t.Fatal(err)
	}
	return out
}

func GetCurrentBranchNameE(t *testing.T) (string, error) {
	cmd := exec.Command("git", "rev-parse", "--abbrev-ref", "HEAD")
	bytes, err := cmd.Output()
	if err != nil {
		return "", err
	}
	return strings.TrimSpace(string(bytes)), nil
}

In most places in our code, we will use GetCurrentBranchName, which will call t.Fatal if it hits any errors. This is typically the behavior we want anyway, and not having to deal with a returned error will keep our code smaller and easier to read. However, in those cases where we may want to get the original error back and not fail the test immediately, we can use GetCurrentBranchNameE.

Other thoughts on the refactor

• Updating to the refactored version of Terratest will be a pain that requires lots of search & replace. But in the long term, it seems like worthwhile cleanup.

• There are a bunch of patterns we often end up using throughout our tests that would be good to copy into Terratest. Anyone remember what those are off the top of our head?

• Having two copies of each method (foo and fooE) is a bit tedious, but the foo variety is essentially the same boilerplate everywhere, so it only increases the maintenance burden on Terratest library maintainers a little, but it improves code readability for all Terratest users enormously.