Comprehensive Terraform Training

COMPREHENSIVE
TRAINING
TERRAFORM
Taught by
Gruntwork
http://gruntwork.io

We’ve pre-written Terraform
packages for the most common
AWS components.
We test, update, and support
these packages.
When a software team
purchases a package, they get
100% of the source code.
Gruntwork

• Network Topology (VPC)
• Monitoring and Alerting
• Docker Cluster
• Continuous Delivery
Sample Packages
Gruntwork

Code samples:
github.com/gruntwork-io/infrastructure-as-code-training

1. Intro
2. State
3. Modules
4. Best practices
5. Gotchas
6. Recap
Outline

Terraform is a tool for
provisioning infrastructure
TERRAFORM

It supports many providers (cloud
agnostic)

And many resources for each
provider

You define resources as code in
Terraform templates

provider "aws" {
region = "us-east-1"
}
resource "aws_instance" "example" {
ami = "ami-408c7f28"
instance_type = "t2.micro"
tags { Name = "terraform-example" }
}
This template creates a single EC2
instance in AWS

> terraform plan
+ aws_instance.example
ami: "" => "ami-408c7f28"
instance_type: "" => "t2.micro"
key_name: "" => "<computed>"
private_ip: "" => "<computed>"
public_ip: "" => "<computed>"
Plan: 1 to add, 0 to change, 0 to destroy.
Use the plan command to see
what you’re about to deploy

> terraform apply
aws_instance.example: Creating...
ami: "" => "ami-408c7f28"
instance_type: "" => "t2.micro"
key_name: "" => "<computed>"
private_ip: "" => "<computed>"
public_ip: "" => "<computed>”
aws_instance.example: Creation complete
Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
Use the apply command to apply
the changes

Now the EC2 instance is running!

You can parameterize your
templates using variables

variable "name" {
description = "The name of the EC2 instance"
}
Define a variable. description,
default, and type are optional.

tags { Name = "${var.name}" }
}
Note the use of ${} syntax to
reference var.name in tags
variable "name" {
}

> terraform plan
var.name
Enter a value: foo
~ aws_instance.example
tags.Name: "terraform-example" => "foo"
Use plan to verify your changes. It
prompts you for the variable.

> terraform apply -var name=foo
aws_instance.example: Refreshing state...
aws_instance.example: Modifying...
tags.Name: "terraform-example" => "foo"
aws_instance.example: Modifications complete
You can also pass variables using
the -var parameter

You can create dependencies
between resources

resource "aws_eip" "example" {
instance = "${aws_instance.example.id}”
}
Notice the use of ${} to depend on
the id of the aws_instance
}

Terraform automatically builds a
dependency graph

You can clean up all resources
you created with Terraform

> terraform destroy
aws_instance.example: Refreshing state... (ID: i-f3d58c70)
aws_elb.example: Refreshing state... (ID: example)
aws_elb.example: Destroying...
aws_elb.example: Destruction complete
aws_instance.example: Destroying...
aws_instance.example: Destruction complete
Just use the destroy command

> terraform destroy
aws_instance.example: Refreshing state... (ID: i-f3d58c70)
aws_elb.example: Refreshing state... (ID: example)
aws_elb.example: Destroying...
aws_elb.example: Destruction complete
aws_instance.example: Destroying...
aws_instance.example: Destruction complete
But how did Terraform know what
to destroy?

Terraform records state of
everything it has done

> ls -al
-rw-r--r-- 6024 Apr 5 17:58 terraform.tfstate
-rw-r--r-- 6024 Apr 5 17:58 terraform.tfstate.backup
By default, state is stored locally
in .tfstate files

> terraform remote config
-backend=s3
-backend-config=bucket=my-s3-bucket
-backend-config=key=terraform.tfstate
-backend-config=encrypt=true
-backend-config=region=us-east-1
You can enable remote state
storage in S3, Atlas, Consul, etc.

Only Atlas provides locking, but it
can be expensive

One alternative: manual
coordination (+ CI job)

Better alternative: terragrunt
github.com/gruntwork-io/terragrunt

Terragrunt is a thin, open source
wrapper for Terraform

It provides locking using
DynamoDB

dynamoDbLock = {
stateFileId = "mgmt/bastion-host"
}
remoteState = {
backend = "s3"
backendConfigs = {
bucket = "acme-co-terraform-state"
key = "mgmt/bastion-host/terraform.tfstate"
}
}
Terragrunt looks for a .terragrunt
file for its configuration.

> terragrunt plan
> terragrunt apply
> terragrunt destroy
Use all the normal Terraform
commands with Terragrunt

> terragrunt apply
[terragrunt] Acquiring lock for bastion-host in DynamoDB
[terragrunt] Running command: terraform apply
aws_instance.example: Creating...
ami: "" => "ami-0d729a60"
instance_type: "" => "t2.micro”
[...]
[terragrunt] Releasing lock for bastion-host in DynamoDB
Terragrunt automatically acquires and
releases locks on apply/destroy

That you can reuse, configure, and
version control

A module is just a folder with
Terraform templates

Most Gruntwork Infrastructure
Packages are Terraform modules

1. vars.tf
2. main.tf
3. outputs.tf

variable "name" {
}
variable "ami" {
description = "The AMI to run on the EC2 instance"
}
variable "port" {
description = "The port to listen on for HTTP requests"
}
Specify module inputs in vars.tf

ami = "${var.ami}"
user_data = "${template_file.user_data.rendered}"
}
Create resources in main.tf

output "url" {
value = "http://${aws_instance.example.ip}:${var.port}"
}
Specify outputs in outputs.tf

See example modules:
gruntwork.io/#what-we-do

module "example_rails_app" {
source = "./rails-module"
}
The source parameter specifies
what module to use

source = "git::git@github.com:foo/bar.git//module?ref=0.1"
}
It can even point to a versioned
Git URL

source = "git::git@github.com:foo/bar.git//module?ref=0.1"
name = "Example Rails App"
ami = "ami-123asd1"
port = 8080
}
Specify the module’s inputs like
any other Terraform resource

module "example_rails_app_stg" {
name = "Example Rails App staging"
}
module "example_rails_app_prod" {
name = "Example Rails App production"
}
You can reuse the same module
multiple times

> terraform get -update
Get: file:///home/ubuntu/modules/rails-module
Get: file:///home/ubuntu/modules/rails-module
Get: file:///home/ubuntu/modules/asg-module
Get: file:///home/ubuntu/modules/vpc-module
Run the get command before
running plan or apply

It’s tempting to define everything
in 1 template
stage
prod
mgmt

But then a mistake anywhere
could break everything
stage
prod
mgmt

What you really want is isolation
for each environment
stage prod mgmt

stage prod mgmt
That way, a problem in stage
doesn’t affect prod

Recommended folder structure
(simplified):

global (Global resources such as IAM, SNS, S3)
└ main.tf
└ .terragrunt
stage (Non-production workloads, testing)
└ main.tf
└ .terragrunt
prod (Production workloads, user-facing apps)
└ main.tf
└ .terragrunt
mgmt (DevOps tooling such as Jenkins, Bastion Host)
└ main.tf
└ .terragrunt

└ main.tf
└ .terragrunt
└ main.tf
└ .terragrunt
└ main.tf
└ .terragrunt
└ main.tf
└ .terragruntEach folder gets its own .tfstate

└ main.tf
└ .terragrunt
└ main.tf
└ .terragrunt
└ main.tf
└ .terragrunt
└ main.tf
└ .terragrunt
Use terraform_remote_state to share
state between them

It’s tempting to define everything
in 1 template
VPC
MySQL
Redis
Bastion
Frontend
Backend

VPC
MySql
Redis
Bastion
Frontend
Backend
But then a mistake anywhere
could break everything

What you really want is isolation
for each component
MySQL VPC Frontend

MySQL VPC Frontend
That way, a problem in MySQL
doesn’t affect the whole VPC

Recommended folder structure
(full):

└ iam
└ sns
└ vpc
└ mysql
└ frontend
└ vpc
└ mysql
└ frontend
└ vpc
└ bastion

└ iam
└ sns
└ vpc
└ mysql
└ frontend
└ vpc
└ mysql
└ frontend
└ vpc
└ bastion
Each component in each environment
gets its own .tfstate

└ iam
└ sns
└ vpc
└ mysql
└ frontend
└ vpc
└ mysql
└ frontend
└ vpc
└ bastion
Use terraform_remote_state to share
state between them

stage
└ vpc
└ mysql
└ frontend
prod
└ vpc
└ mysql
└ frontend
How do you avoid copy/pasting code
between stage and prod?

stage
└ vpc
└ mysql
└ frontend
prod
└ vpc
└ mysql
└ frontend
modules
└ vpc
└ mysql
└ frontend
Define reusable modules!

stage
└ vpc
└ mysql
└ frontend
prod
└ vpc
└ mysql
└ frontend
modules
└ vpc
└ mysql
└ frontend
└ main.tf
└ outputs.tf
└ vars.tf
Each module defines one reusable
component

variable "name" {
}
variable "ami" {
description = "The AMI to run on the EC2 instance"
}
variable "memory" {
description = "The amount of memory to allocate"
}
Define inputs in vars.tf to
configure the module

module "frontend" {
source = "./modules/frontend"
name = "frontend-stage"
ami = "ami-123asd1"
memory = 512
}
Use the module in stage
(stage/frontend/main.tf)

module "frontend" {
source = "./modules/frontend"
name = "frontend-prod"
ami = "ami-123abcd"
memory = 2048
}
And in prod
(prod/frontend/main.tf)

stage
└ vpc
└ mysql
└ frontend
prod
└ vpc
└ mysql
└ frontend
modules
└ vpc
└ mysql
└ frontend
If stage and prod point to the
same folder, you lose isolation

stage
└ vpc
└ mysql
└ frontend
prod
└ vpc
└ mysql
└ frontend
modules
└ vpc
└ mysql
└ frontend
Any change in modules/frontend
affects both stage and prod

infrastructure-live
└ stage
└ vpc
└ mysql
└ frontend
└ prod
└ vpc
└ mysql
└ frontend
infrastructure-modules
└ vpc
└ mysql
└ frontend
Solution: define modules in a
separate repository

infrastructure-live
└ stage
└ vpc
└ mysql
└ frontend
└ prod
└ vpc
└ mysql
└ frontend
infrastructure-modules
└ vpc
└ mysql
└ frontend
Now stage and prod can use
different versioned URLs
0.1
0.2

module "frontend" {
source =
"git::git@github.com:foo/infrastructure-
modules.git//frontend?ref=0.2"
name = "frontend-prod"
ami = "ami-123abcd"
memory = 2048
}
Example Terraform code
(prod/frontend/main.tf)

Use terragrunt
github.com/gruntwork-io/terragrunt

dynamoDbLock = {
stateFileId = "mgmt/bastion-host"
}
Use a custom lock (stateFileId) for
each set of templates

remoteState = {
backend = "s3"
backendConfigs = {
bucket = "acme-co-terraform-state"
key = "mgmt/bastion-host/terraform.tfstate"
encrypt = "true"
}
}
Use an S3 bucket with encryption for
remote state storage

Enable versioning on the S3 bucket!

Terraform is declarative, so very
little “logic” is possible…

But you can “loop” to create
multiple resources using count

count = 1
ami = "${var.ami}"
}
Create one EC2 Instance

count = 3
ami = "${var.ami}"
}
Create three EC2 Instances

Use count.index to modify each
“iteration”

count = 3
ami = "${var.ami}"
tags { Name = "${var.name}-${count.index}" }
}
Create three EC2 Instances, each
with a different name

Do even more with interpolation
functions:
terraform.io/docs/configuration/interpolation.html

count = 3
ami = "${element(var.amis, count.index)}"
tags { Name = "${var.name}-${count.index}" }
}
variable "amis" {
type = "list"
default = ["ami-abc123", "ami-abc456", "ami-abc789"]
}
Create three EC2 Instances, each
with a different AMI

output "all_instance_ids" {
value = ["${aws_instance.example.*.id}"]
}
output "first_instance_id" {
value = "${aws_instance.example.0.id}"
}
Note: resources with count are
actually lists of resources!

But you can do a limited form of
if-statement using count

count = "${var.should_create_instance}"
ami = "ami-abcd1234"
}
variable "should_create_instance" {
default = true
}
Note the use of a boolean in the
count parameter

In HCL:
• true = 1
• false = 0

}
default = true
}
So this creates 1 EC2 Instance if
should_create_instance is true

}
default = true
}
Or 0 EC2 Instances if
should_create_instance is false

It’s equivalent to:
if (should_create_instance)
create_instance()

There are many permutations of
this trick (e.g. using length)

Valid plan to create IAM instance
profiles
> terraform plan
+ aws_iam_instance_profile.instance_profile
arn: "<computed>"
create_date: "<computed>"
name: "stage-iam-nat-role"
path: "/"
roles.2760019627: "stage-iam-nat-role"
unique_id: "<computed>”
Plan: 1 to add, 0 to change, 0 to destroy.

But the instance profile already
exists in IAM!

You get an error
> terraform apply
Error applying plan:
* Error creating IAM role stage-iam-nat-role:
EntityAlreadyExists: Role with name stage-iam-nat-role already
exists
status code: 409, requestId: [e6812c4c-6fac-495c-be9d]

Conclusion: Never make out-of-
band changes.

2. AWS is eventually consistent

Terraform doesn’t always wait for
a resource to propagate

Which causes a variety of
intermittent bugs:

> terraform apply
...
* aws_route.internet-gateway:
error finding matching route for Route table (rtb-5ca64f3b)
and destination CIDR block (0.0.0.0/0)

> terraform apply
...
* Resource 'aws_eip.nat' does not have attribute 'id' for
variable 'aws_eip.nat.id'

> terraform apply
...
* aws_subnet.private-persistence.2: InvalidSubnetID.NotFound:
The subnet ID 'subnet-xxxxxxx' does not exist

> terraform apply
...
* aws_route_table.private-persistence.2:
InvalidRouteTableID.NotFound: The routeTable ID 'rtb-2d0d2f4a'
does not exist

> terraform apply
...
* aws_iam_instance_profile.instance_profile: diffs didn't
match during apply. This is a bug with Terraform and should be
reported.
* aws_security_group.asg_security_group_stg: diffs didn't
match during apply. This is a bug with Terraform and should be
reported.
The most generic one: diffs didn’t
match during apply

Most of these are harmless. Just
re-run terraform apply.

And try to run Terraform close to
your AWS region (replica lag)

resource "aws_route_table" "main" {
vpc_id = "${aws_vpc.main.id}"
route {
cidr_block = "10.0.1.0/24"
gateway_id = "${aws_internet_gateway.main.id}"
}
}
Some resources allow blocks to
be defined inline…

}
resource "aws_route" "internet" {
route_table_id = "${aws_route_table.main.id}"
cidr_block = "10.0.1.0/24"
}
Or in a separate resource

}
cidr_block = "10.0.1.0/24"
}
Pick one technique or the other
(separate resource is preferable)

}
cidr_block = "10.0.1.0/24"
}
If you use both, you’ll get
confusing errors!

Affected resources:
• aws_route_table
• aws_security_group
• aws_elb
• aws_network_acl

There is a significant limitation
on the count parameter:

You cannot compute count from
dynamic data

Example: this code won’t work
data "aws_availability_zones" "zones" {}
resource "aws_subnet" "public" {
count = "${length(data.aws_availability_zones.zones.names)}"
cidr_block = "${cidrsubnet(var.cidr_block, 5, count.index}"
availability_zone =
"${element(data.aws_availability_zones.zones.names,
count.index)}"
}

> terraform apply
...
* strconv.ParseInt: parsing
"${length(data.aws_availability_zones.zones.names)}": invalid
syntax

data.aws_availability_zones
won’t work since it fetches data
count = "${length(data.aws_availability_zones.zones.names)}"
availability_zone =
count.index)}"
}

A fixed number is OK
count = 3
availability_zone =
count.index)}"
}

So is a hard-coded variable
count = "${var.num_availability_zones}"
availability_zone =
count.index)}"
}
variable "num_availability_zones" {
default = 3
}

For more info, see:
github.com/hashicorp/terraform/issues/3888

Advantages of Terraform:
1. Define infrastructure-as-code
2. Concise, readable syntax
3. Reuse: inputs, outputs, modules
4. Plan command!
5. Cloud agnostic
6. Very active development

Disadvantages of Terraform:
1. Maturity. You will hit bugs.
2. Collaboration on Terraform state is
tricky (but not with terragrunt)
3. No rollback
4. Poor secrets management

Questions?
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