Note: This is an early release version of the contents of the Navigator’s Guide book, an offering from the DigitalOcean Solutions Engineers. The goal of the book is to help business customers plan their infrastructure needs, provide working examples along the way, and include technical nuance and the “why” that makes some decisions better than others.
The book and accompanying code will be publicly available in a GitHub repository. Because this is an early release, the book is not yet complete and the repository is not yet public, but stay tuned!
This is the first hands-on portion of the book.
First, we’ll go over the tools we’ll be using, how they fit together, and how they can be beneficial to you as you begin to create and manage your infrastructure on DigitalOcean. After that, we’ll set up a single Droplet which we’ll use as a controller to run and use the rest of our tools.
Terraform is an open-source tool that allows you to easily describe your infrastructure as code. This means you can version control your resources in the same way you would if you were writing a program, which allows you to roll back to a working state if you hit an error.
Terraform uses a declarative syntax (HCL) that is designed to be easy for humans and computers alike to understand. HCL lets you plan your changes for review and automatically handles infrastructure dependencies for you.
We’ll be using Terraform to create our infrastructure — that is, creating Droplets, Reserved IPs, Firewalls, Block Storage Volumes, and DigitalOcean Load Balancers — but we won’t be using it to configure those resources. That’s where Ansible comes in.
There are a few resources we recommend if you would like to learn more about Terraform:
Ansible is a configuration management tool which allows you to systematically handle changes to a system in a way that maintains its integrity over time. Ansible’s standard library of modules is extensive, and its architecture allows you to create your own plugins as well.
Ansible playbooks are YAML files which define the automation you want to manage. Like Terraform, you can version control your playbooks. Unlike Terraform, a change in the configuration of a resource does not require the destruction and recreation of that resource; Ansible pushes configurations to your infrastructure.
Ansible uses SSH connections, so you don’t need to install an agent on the target nodes to use it. However, that does mean Ansible needs to know which endpoints to connect to, which is typically defined with an inventory file. Because we’re using Terraform to deploy, and it maintains your infrastructure state in a file, we’ll use terraform-inventory to dynamically feed Ansible its list of target machines.
Ansible playbooks call modules to make configuration changes or execute commands. There are many built-in modules for Ansible to control popular software or cloud vendors, including DigitalOcean. When working in the command line, the
ansible-doc command is an easy way to review the options and details for modules. An example would be
ansible-doc -l to list the modules or calling a specific module to see the documentation,
ansible-doc digital_ocean. Playbooks can be packages as roles for easy sharing. The main public repository for roles is Ansible Galaxy. The code examples in this book utilize multiple roles for applying configurations.
It is worth noting that Ansible is not enforcing state. Executing a playbook will only run the commands in the playbook. Making changes directly to the servers being managed by Ansible may result in unintended consequences.
There are a few resources we recommend if you would like to learn more about Ansible. Red Hat owns the Ansible project and offers training options. This includes a great introduction video class for free as well as more advanced classes:
terraform-inventory is a dynamic inventory script that pulls resource information from Terraform’s state file and outputs it in a way that Ansible can use to target specific hosts when executing playbooks. It gets a little more complicated than that, but the key point is that
terraform-inventory makes it easier for you to use Terraform and Ansible together.
We’ll use Git as our version control system. You don’t need in-depth knowledge of Git in particular, but understanding committing changes, tracking, and cloning. Because we can version control our Terraform and Ansible files, we can run tests on different versions of our infrastructure by specifying a version of a Terraform module or Ansible role.
The DigitalOcean CLI utility,
doctl, is often helpful in quickly accessing your account through the API to create or retrieve resource information. You can find instructions to set up
doctl in the project README and full usage information in its official documentation.
Our controller machine is the server we’ll use to run our tools. We’ll use an Ubuntu 18.04 x64 (Bionic Beaver) Droplet, which we’ll configure to install all the tools we need as the Droplet is being created.
Note: If you’re more comfortable using another operating system (like macOS on your local computer), you can do that instead as long as it meets Ansible’s system requirements.
To start, you’ll need:
Now it’s time to create the Droplet. We’ll be using the following options::
When you select the user data option, a text field will open up. User data is arbitrary data that a user can supply to a Droplet at creation time. User data is consumed by CloudInit, typically during the first boot of a cloud server, to perform tasks or run scripts as the root user.
We’ll use a cloud-config script to install Python 2.7,
pip (a Python package manager), Git,
terraform-inventory, and Ansible.
Note: You can also install this software manually if you prefer. Terraform and
terraform-inventoryare Go binaries that need to be placed within your
$PATH. We recommend installing Ansible with Pip instead of a system package manager like APT because it stays up to date and allows you to install it within a
# Source: https://git.io/nav-guide-cloud-config
- [curl, -o, /tmp/terraform.zip, "https://releases.hashicorp.com/terraform/0.11.7/terraform_0.11.7_linux_amd64.zip"]
- [unzip, -d, /usr/local/bin/, /tmp/terraform.zip]
- [curl, -L, -o, /tmp/terraform-inventory.zip, "https://github.com/adammck/terraform-inventory/releases/download/v0.7-pre/terraform-inventory_v0.7-pre_linux_amd64.zip"]
- [unzip, -d, /usr/local/bin/, /tmp/terraform-inventory.zip]
- [pip, install, -U, pip, ansible]
- [git, clone, "https://github.com/digtialocean/navigators-guide.git"]
From here, click Create. The Droplet itself will be up and running quickly, but the commands in its user data will take a little time to finish running. You can log into the Droplet and look at
/var/log/cloud-init-output.log to check its status.
The last step is to create an SSH key for the controller Droplet. We’ll later place this on each of the nodes in our infrastructure. You can run this one-liner when logged into your server to create a key and comment it with your Droplet’s hostname:
ssh-keygen -t rsa -C $(hostname -f)
You’ll be able to see the public and private key pair in
Your controller Droplet is set up, which means you can start using the tools. In the next chapter, we’ll show you how to use those tools to start creating a highly available infrastructure. In doing so, you’ll start seeing the difference between Ansible and Terraform.
Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.
This is an early release version of the contents of the Navigator’s Guide book, an offering from the DigitalOcean Solutions Engineers. The goal of the book is to help business customers plan their infrastructure needs, provide working examples along the way, and include technical nuance and the “why” that makes some decisions better than others.
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