Getting Started

Build Infrastructure

With Terraform installed, let's dive right into it and start creating some infrastructure.

We'll build infrastructure on AWS for the getting started guide since it is popular and generally understood, but Terraform can manage many providers, including multiple providers in a single configuration. Some examples of this are in the use cases section.

If you don't have an AWS account, create one now. For the getting started guide, we'll only be using resources which qualify under the AWS free-tier, meaning it will be free. If you already have an AWS account, you may be charged some amount of money, but it shouldn't be more than a few dollars at most.

» Configuration

The set of files used to describe infrastructure in Terraform is simply known as a Terraform configuration. We're going to write our first configuration now to launch a single AWS EC2 instance.

The format of the configuration files is documented here. Configuration files can also be JSON, but we recommend only using JSON when the configuration is generated by a machine.

The entire configuration is shown below. We'll go over each part after. Save the contents to a file named example.tf. Verify that there are no other *.tf files in your directory, since Terraform loads all of them.

provider "aws" {
  access_key = "ACCESS_KEY_HERE"
  secret_key = "SECRET_KEY_HERE"
  region     = "us-east-1"
}

resource "aws_instance" "example" {
  ami           = "ami-2757f631"
  instance_type = "t2.micro"
}

Replace the ACCESS_KEY_HERE and SECRET_KEY_HERE with your AWS access key and secret key, available from this page. We're hardcoding them for now, but will extract these into variables later in the getting started guide.

This is a complete configuration that Terraform is ready to apply. The general structure should be intuitive and straightforward.

The provider block is used to configure the named provider, in our case "aws". A provider is responsible for creating and managing resources. Multiple provider blocks can exist if a Terraform configuration is composed of multiple providers, which is a common situation.

The resource block defines a resource that exists within the infrastructure. A resource might be a physical component such as an EC2 instance, or it can be a logical resource such as a Heroku application.

The resource block has two strings before opening the block: the resource type and the resource name. In our example, the resource type is "aws_instance" and the name is "example." The prefix of the type maps to the provider. In our case "aws_instance" automatically tells Terraform that it is managed by the "aws" provider.

Within the resource block itself is configuration for that resource. This is dependent on each resource provider and is fully documented within our providers reference. For our EC2 instance, we specify an AMI for Ubuntu, and request a "t2.micro" instance so we qualify under the free tier.

» Initialization

The first command to run for a new configuration -- or after checking out an existing configuration from version control -- is terraform init, which initializes various local settings and data that will be used by subsequent commands.

Terraform uses a plugin based architecture to support the numerous infrastructure and service providers available. As of Terraform version 0.10.0, each "Provider" is its own encapsulated binary distributed separately from Terraform itself. The terraform init command will automatically download and install any Provider binary for the providers in use within the configuration, which in this case is just the aws provider:

$ terraform init
Initializing the backend...
Initializing provider plugins...
- downloading plugin for provider "aws"...

The following providers do not have any version constraints in configuration,
so the latest version was installed.

To prevent automatic upgrades to new major versions that may contain breaking
changes, it is recommended to add version = "..." constraints to the
corresponding provider blocks in configuration, with the constraint strings
suggested below.

* provider.aws: version = "~> 1.0"

Terraform has been successfully initialized!

You may now begin working with Terraform. Try running "terraform plan" to see
any changes that are required for your infrastructure. All Terraform commands
should now work.

If you ever set or change modules or backend configuration for Terraform,
rerun this command to reinitialize your environment. If you forget, other
commands will detect it and remind you to do so if necessary.

The aws provider plugin is downloaded and installed in a subdirectory of the current working directory, along with various other book-keeping files.

The output specifies which version of the plugin was installed, and suggests specifying that version in configuration to ensure that running terraform init in future will install a compatible version. This step is not necessary for following the getting started guide, since this configuration will be discarded at the end.

» Apply Changes

In the same directory as the example.tf file you created, run terraform apply. You should see output similar to below, though we've truncated some of the output to save space:

$ terraform apply
# ...

+ aws_instance.example
    ami:                      "ami-2757f631"
    availability_zone:        "<computed>"
    ebs_block_device.#:       "<computed>"
    ephemeral_block_device.#: "<computed>"
    instance_state:           "<computed>"
    instance_type:            "t2.micro"
    key_name:                 "<computed>"
    placement_group:          "<computed>"
    private_dns:              "<computed>"
    private_ip:               "<computed>"
    public_dns:               "<computed>"
    public_ip:                "<computed>"
    root_block_device.#:      "<computed>"
    security_groups.#:        "<computed>"
    source_dest_check:        "true"
    subnet_id:                "<computed>"
    tenancy:                  "<computed>"
    vpc_security_group_ids.#: "<computed>"

This output shows the execution plan, describing which actions Terraform will take in order to change real infrastructure to match the configuration. The output format is similar to the diff format generated by tools such as Git. The output has a + next to aws_instance.example, meaning that Terraform will create this resource. Beneath that, it shows the attributes that will be set. When the value displayed is <computed>, it means that the value won't be known until the resource is created.

If terraform apply failed with an error, read the error message and fix the error that occurred. At this stage, it is likely to be a syntax error in the configuration.

If the plan was created successfully, Terraform will now pause and wait for approval before proceeding. If anything in the plan seems incorrect or dangerous, it is safe to abort here with no changes made to your infrastructure. In this case the plan looks acceptable, so type yes at the confirmation prompt to proceed.

Executing the plan will take a few minutes since Terraform waits for the EC2 instance to become available:

# ...
aws_instance.example: Creating...
  ami:                      "" => "ami-2757f631"
  instance_type:            "" => "t2.micro"
  [...]

aws_instance.example: Still creating... (10s elapsed)
aws_instance.example: Creation complete

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

# ...

After this, Terraform is all done! You can go to the EC2 console to see the created EC2 instance. (Make sure you're looking at the same region that was configured in the provider configuration!)

Terraform also wrote some data into the terraform.tfstate file. This state file is extremely important; it keeps track of the IDs of created resources so that Terraform knows what it is managing. This file must be saved and distributed to anyone who might run Terraform. It is generally recommended to setup remote state when working with Terraform, to share the state automatically, but this is not necessary for simple situations like this Getting Started guide.

You can inspect the current state using terraform show:

$ terraform show
aws_instance.example:
  id = i-32cf65a8
  ami = ami-2757f631
  availability_zone = us-east-1a
  instance_state = running
  instance_type = t2.micro
  private_ip = 172.31.30.244
  public_dns = ec2-52-90-212-55.compute-1.amazonaws.com
  public_ip = 52.90.212.55
  subnet_id = subnet-1497024d
  vpc_security_group_ids.# = 1
  vpc_security_group_ids.3348721628 = sg-67652003

You can see that by creating our resource, we've also gathered a lot of information about it. These values can actually be referenced to configure other resources or outputs, which will be covered later in the getting started guide.

» Provisioning

The EC2 instance we launched at this point is based on the AMI given, but has no additional software installed. If you're running an image-based infrastructure (perhaps creating images with Packer), then this is all you need.

However, many infrastructures still require some sort of initialization or software provisioning step. Terraform supports provisioners, which we'll cover a little bit later in the getting started guide, in order to do this.