Intro

Terraform is a excellent tool to provide infrastructure as code in your organization. Commonly, it is use to work in cloud infrastructure environments, however it can also be used with others providers (not only cloud providers), one example is use docker service as a provider.

Some terms of use are explained below:

• A provider is an abstract way of handling the underlying infrastructure responsible for managing the lifecycle of a resource. E.g. docker, aws, etc

• A resource are components of your infrastructure, for example a container or image.

Define a provider to use

cat > config.tf << EOF
provider "docker" {
  host = "unix:///var/run/docker.sock"
}
EOF

Declare the resources to create

One first resource is our docker image. A resource has two parameters:

• one is a TYPE and
• the another is the NAME.

In our case, type is docker_image and name as nginx.

cat >> config.tf << EOF
resource "docker_image" "nginx" {
  name = "nginx:1.11-alpine"
}
EOF

Other resource type is docker_container name as nginx-server. Within the block we set the resource parameters. We can reference other resources, such as a the image.

cat >> config.tf << EOF
resource "docker_container" "nginx-server" {
  name = "nginx-server-1"
  image = docker_image.nginx.latest
  ports {
    internal = 80
    external = 8081
  }
  volumes {
    container_path  = "/usr/share/nginx/html"
    host_path = "/tmp/tutorial/www"
    read_only = true
  }
}
EOF

Terraform Actions

Terraform describes the actions required to achieve the desired state. We have “init”, “plan” and “apply” more known actions.

The plan can be saved using -out.

Initializing our project

terraform init

And then, we plan our state desired

terraform plan -out config.tfplan

The output of the command indicates the changes. In this case, you’ll see a dockercontainer.nginx-server and dockerimage.nginx to highlight adding the new resources. Finally a summary of Plan: 2 to add, 0 to change, 0 to destroy.

To create some data for our containers, we added some content:

mkdir -p /tmp/tutorial/www
echo "<h1>hello world</h1>" > /tmp/tutorial/www/index.html

Apply

Once the plan has been created we need to apply it to reach our desired state.

terraform will pull the image required and launch the new containers.

terraform apply

Inspect your container

Using the docker command to see the changes and the newly launched container.

docker ps
docker ps -f name=nginx-server-1 --format "table {{.Names}}\t{{.Status}}"

You can inspect this in future using the terraform CLI

terraform show

Testing with curl

curl http://localhost:8081
firefox http://localhost:8081

Some changes

As our infrastructure grows and changes, terraform will manage and ensure we always have our defined desired state.

We can change our container to launch two instances, each with different names.

resource "docker_container" "nginx-server" {
  count = 2
  name = "nginx-server-${count.index+1}"
  image = docker_image.nginx.latest
  ports {
    internal = 80
    external = "808${count.index+1}"
  }
  volumes {
    container_path  = "/usr/share/nginx/html"
    host_path = "/tmp/tutorial/www"
    read_only = true
  }
}

If we create a plan you will see the actions Terraform will need to apply to adapt our infrastructure to match our configuration.

terraform validate
terraform plan -out config.tfplan

The plan will outline the changes. Because we’re changing the name and adding a resource we’ll see Plan: 1 to add, 0 to change, 0 to destroy.

In the details it will explain that changing a container name forces the resource to be recreated name: “nginx-server” => “nginx-server-1” (forces new resource) along with adding the new container dockercontainer.nginx-server.1

We can then apply the plan as we did in the previous step.

terraform apply -auto-approve

Now, we scale our nginx-server up to 8 replicas:

resource "docker_container" "nginx-server" {
  count = 8
  name = "nginx-server-${count.index+1}"
  image = docker_image.nginx.latest
  ports {
    internal = 80
    external = "808${count.index+1}"
  }
  volumes {
    container_path  = "/usr/share/nginx/html"
    host_path = "/tmp/tutorial/www"
    read_only = true
  }
}

terraform plan
terraform apply -auto-approve

Clean up

terraform destroy
rm -rf config.tf* terraform.tfstate* .terraform/
rm -rf /tmp/tutorial

Demo

References

• https://www.terraform.io/docs/providers/docker/index.html
• https://gist.github.com/brianshumate/09adf967c563731ca1b0c4d39f7bcdc2