Terraform and Ansible are the most widely used Infrastructure as Code (IaC) tools. Comparisons between the two are common, and most DevOps teams tend to choose one based on their immediate requirements.
With the number of articles comparing Terraform to Ansible out there, one might think that selecting a tool is a cut and dry decision. But the true power of these tools lies in using them together. In this article, we’ll explain why Terraform, with its declarative approach to infrastructure provisioning, perfectly complements Ansible’s imperative model for configuration management.
Understanding Terraform’s Declarative Approach
A declarative approach in programming is when users “declare” or define the outcome of their code without specifying the steps the program takes to get there. So, in Terraform, users can define the desired states of their infrastructure by simply describing resources like servers, networks, and storage in terms of their end state.
Terraform operates with state files, and each time you execute a command, it will compare the current state of the infrastructure (as recorded in the state file) with the desired state defined in the configuration file. If there is a difference, Terraform generates a plan to reconcile the two, which may include updating, creating, or deleting resources to match the declared configuration.
There are several benefits to Terraform’s declarative approach. First and foremost, it’s simple. Imagine if you could get anything you want in life without really planning how to get it. That’s exactly what Terraform allows you to do, significantly reducing the complexity of infrastructure management.
This simplicity extends to predictability and scalability. Running the same configuration multiple times produces consistent results, which is ideal for scaling across multiple environments.
What’s more, Terraform’s reliance on state files ensures that every change to the configuration is tracked, which helps avoid conflicts when multiple team members are collaborating on infrastructure updates.
Understanding Ansible’s Imperative Approach
Contrary to Terraform, Ansible utilizes an imperative programming approach. With the imperative model, users define the specific steps needed to achieve a configuration, giving them complete control over not just the end result but also on how to get there.
If you compare an Ansible configuration file and one from Terraform, you will notice that there is a lot more detail in Ansible, including specific commands specifying what, where, and how to utilize resources and perform tasks.
This may put off some people due to the perceived complexity, but there are some situations where this level of detail and control is essential. For example, to configure a firewall, you need to specify exact rules, including open ports, group policies, IP ranges, and protocols. The only way to do so is by defining the rules step by step.
Another benefit to Ansible is that it is completely agentless, meaning that it doesn’t require any additional software or agents to be installed on the target machines. Instead, it uses protocols like SSH to communicate with and execute tasks on remote systems.
How Ansible and Terraform Complement Each Other
Focusing on what tool is “better” than the other is pointless, because both tools excel in unique areas that are ideal for different situations.
It’s like saying that everyone should choose a hammer over a screwdriver. Yes, hammers are great and have many uses, but you can’t turn a screw with a hammer. It’s best to have both tools available, and use them interchangeably depending on what you want to achieve.
Terraform is ideal for provisioning and managing infrastructure as a single source of truth, while Ansible is best for configuring, updating, and managing systems once the main infrastructure is in place. In programming terms, Terraform excels at Day 0 tasks (provisioning infrastructure), while Ansible at Day N tasks (ongoing configuration and updates).
By using Terraform and Ansible in tandem, you can streamline your infrastructure management from end to end, with each tool handling the tasks it excels at. Use Terraform to define and deploy the initial infrastructure, which may include virtual machines, networks, storage, or a multi-cloud setup. Once the infrastructure is provisioned, use Ansible to configure the systems, install software, apply security patches, and manage updates.
This unlocks the full potential of Infrastructure as Code. Once your team gets used to using both tools interchangeably, there will be vast improvements in the efficiency, consistency, and scalability of your infrastructure management processes.
Real-World Scenarios for Combining Ansible and Terraform
Let’s look at two relevant examples of how combining Terraform and Ansible simplifies infrastructure creation and management.
We’ll start with a multi-cloud setup, since that is a common use case. In a multi-cloud environment, organizations use resources from multiple providers. This can quickly become complicated as the providers have independent APIs, configurations, and management tools.
But with Terraform, you can provision all of the underlying resources consistently across both providers. Then, Ansible takes over to uniformly configure these resources with the appropriate software, security, and system settings.
Another scenario where both tools excel is disaster recovery. Organizations need a reliable way to recover and restore their infrastructure and configuration after unforeseen events. You can store your Terraform state files in a secure and accessible location, such as a different cloud region, where it will be readily available to be redeployed, by only changing a few configuration details.
The same can be said about Ansible, the only difference being that you’re not working with state files, but rather with playbooks. The playbooks can be stored in a version-controlled repository where they can be accessed and executed as needed.
Best Practices for Using Ansible and Terraform Together
To maximize the potential benefits of combining Ansible and Terraform, consider the following best practices.
Firstly, it’s important to establish clear boundaries about which tasks are handled by each tool. As discussed throughout the article, use Terraform for provisioning, and Ansible for configuring. This way, you’re playing on the strengths of each tool.
On the same note, avoid using both tools for the same tasks. For example, don’t configure the same network settings in both Terraform and Ansible. Instead, let Terraform handle infrastructure-level changes and Ansible manage system-level configurations.
To improve reusability, take advantage of Terraform modules and Ansible roles. Modules are reusable configurations you can apply across common infrastructure components, while roles allow you to reuse Ansible tasks and apply them consistently.
Conclusion
If you’re trying to maximize the efficiency of your DevOps team’s IaC operations, you have to use all the tools available. Sticking to just one because of familiarity or convenience sets you back in the ability to properly manage the full lifecycle of infrastructure management.
By using both tools – Terraform for provisioning and state management, and Ansible for configuration and updates – you will create a more streamlined, reliable, and scalable process.
