Terraform vs Ansible: Their Differences, and When to Use or Not Use Them

What Is Terraform?

Terraform’s product website describes it as “…an infrastructure as code (IaC) tool that allows you to build, change, and version infrastructure safely and efficiently. This includes low-level components such as compute instances, storage, and networking, as well as high-level components such as DNS entries, SaaS features, etc. Terraform can manage both existing service providers and custom in-house solutions.”

It is an open-source platform made for building, changing, and versioning infrastructure effectively and securely and is very straightforward.

What Is Ansible?

According to Red Hat, Ansible is “…an open-source IT automation engine that automates provisioning, configuration management, application deployment, orchestration, and many other IT processes.”

Ansible is a configuration management tool that focuses on deploying and provisioning applications with IaC.

Terraform vs Ansible: Similarities and Differences

Before we start comparing Terraform and Ansible, let's get one thing straight: these tools are designed to accomplish different things, and their feature sets don't align precisely. So, this exercise isn't an exact head-to-head comparison, such as comparing Microsoft Excel with Google Sheets.

Here’s a handy reference chart that breaks down the similarities and differences between Terraform vs Ansible.

 Let’s look closer at some specific similarities and differences between Terraform vs Ansible.

Similarities: Terraform vs Ansible 

Both Terraform and Ansible allow provisioning of infrastructure using Infrastructure as Code, so we can say that they are both used as IaC platforms.

Additionally, both tools can execute remote commands on a newly created virtual machine. Or, to put it another way, both are agentless.

Orchestration and provisioning is when users create the infrastructure, including virtual machines, databases, network components, and other resources. On the other hand, configuration management automates versioned software component installation, operating system configuration tasks, network and firewall configuration, and related tasks. Although Terraform and Ansible can perform configuration management tasks, the latter does a far better job.

They also both work with cloud APIs and are both open-source. Developers can also use Terraform and Ansible simultaneously, so the two tools complement each other rather than replace each other. More on this idea later.

Differences: Terraform vs Ansible

There are a lot of differences between Terraform and Ansible. Here are the key ones, laid out in a more organized format:

• Declarative vs. Imperative: The first thing we should tackle is the declarative versus the imperative approach. For example, if you wanted to create ten web servers using Terraform, you’d say, “I want to create ten web servers.” That is a declarative statement. However, if you were using Ansible, you would say, “If these web servers don’t exist already, create one first, then create the other nine.” That is a declarative statement.
• Immutable vs. Mutable: You cannot change an immutable server. Users who want to make changes in an immutable virtual server destroy the old version and replace it with the version that encompasses the changes. A mutable virtual server allows users to make changes without blowing up the whole server. Ansible emphasizes mutability, while Terraform is considered immutable. However, these conditions are defaults; both tools can conduct mutable operations and have immutable elements to one degree or another.
• Provisioning: Terraform is geared towards infrastructure automation and interprets models described in HCL. With Terraform, the required environment elements (e.g., networks, servers, etc.) are separately described, along with their relationships to one another. Then, Terraform assesses and evaluates the model, develops a plan based on dependencies, and delivers optimized commands to the IaaS (Infrastructure as a Service). Repeated runs do nothing if there are no changes in the environment or plan. However, any update in the plan or environment synchronizes the cloud infrastructure to the new plan's intent.

Ansible follows a procedural or imperative approach. Users create "playbooks" that are evaluated via a top-to-bottom approach and executed in sequence. Playbooks are typically responsible for configuring individual hosts and network devices that facilitate a procedural process. Ansible can also provision the cloud infrastructure, but its procedural nature limits it to larger infrastructural deployments.

Since Ansible is ideal for configuration management, it's not limited to cloud applications; it can configure bare metal servers and virtual ones.

When Should You NOT Use Ansible or Terraform?

Here are the scenarios in which you don’t want to use Ansible or Terraform.

• Ansible: If configuration drift is an issue for you, don’t use Ansible. Configuration drift occurs when users change settings so that new versions of the virtual infrastructure “drift” away from the original configuration.
• Terraform: If you’re using images to provision VMs, you may require dozens of images to accommodate your application servers, messaging servers, web servers, etc. Since Terraform doesn’t allow you to change the images themselves, you need an image with the exact state you want. If you’re making three changes a day for each day of the working week in your server, that’s fifteen copies of the server! That’s a lot of storage space.

Conclusion: Terraform or Ansible?

So, which one is better? It depends on what you’re looking for and what features matter to you. If you’re looking for a user-friendly tool with good scheduling capabilities and smooth Docker integration, then go with Terraform. On the other hand, if you’re more interested in security, good ACL functionality, and something that plays well with traditional automated frameworks, then Ansible’s your answer.

Not Terraform vs Ansible but Terraform and Ansible

Why settle for one or the other? It’s possible to use both Terraform and Ansible! Ansible does an excellent job handling provisioning and configuration management. Terraform excels in provisioning infrastructure across multiple cloud platforms, with support for many providers.

You can combine Terraform for its orchestration strengths, creating your needed resources and services, then turn to Ansible for its configuration management of your infrastructure, and enjoy the best of both worlds.

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