Infrastructure as Code (IaC) has revolutionized how DevOps-focused organizations manage their IT resources, enabling faster cloud deployments and automated configurations using scripts. Two of the most popular IaC are Ansible and Terraform.
While both of these tools have the same main goal of automating infrastructure, they do differ significantly in their approach to doing so. In this article, we will focus on the three most pivotal differences between Ansible and Terraform, with the aim of helping you make the right choice for your situation.
1. Dealing With Configuration Drift
Configuration drift is one of the most critical areas to address in IaC. It refers to situations where the actual output of a configuration is different to the desired state defined in the code. This discrepancy can lead to inconsistencies, security risk, and overall operational inefficiency.
In Ansible, configuration drift is addressed by continuous enforcement of the desired state. This is done via playbooks written in YAML, which contain the desired configurations and actions for your infrastructure. Every time you run a playbook, Ansible will ensure that it matches the specified state inside that playbook.
Let’s say you have a playbook that runs an Apache HTTP server with specific settings. If someone manually stops the server or makes a different change, running the playbook will correct these issues and maintain the desired state.
By scheduling playbooks to run periodically, or whenever there’s configuration change, you can ensure the consistency of your infrastructure as defined in those playbooks, preventing configuration drift.
Terraform has a slightly different approach to dealing with configuration drift. Here, the user has a state file which contains both the desired and actual states, allowing the tool to quickly identify discrepancies by comparing the two states.
This comparison is done by running the terraform plan command, which outlines potential discrepancies between the current and desired state, along with an execution plan that shows the changes Terraform will make to correct the drift. Terraform will only execute these changes if you manually approve the plan by using the terraform apply command.
Both Ansible and Terraform provide powerful solutions for dealing with configuration drift. While one approach isn’t better than the other, each may be more suitable for specific environments.
Ansible’s focus on continuous enforcement makes it ideal for environments where there are frequent updates, or that require real-time configuration enforcement. Its idempotency ensures that the desired state is always maintained, even when playbooks are run multiple times.
On the other hand, Terraform’s state management and detailed execution plans make it well suited for environments where mistakes can be costly, such as large-scale enterprise infrastructure or multi-cloud deployments.
2. Procedural vs. Declarative Configuration Structure
The next difference we will discuss has to do with the syntax of the code and how it executes to manage resources.
Ansible uses procedural programming language, meaning that the code specifies a step-by-step process for achieving the desired state. As mentioned before, Ansible uses playbooks written in YAML code. That is where each task is defined and organized in a sequence, allowing for clear control over the order of operation and execution.
This procedural approach is ideal for complex workflows and tasks that require precise control over each step. If you want to run an Apache server with specific settings, for example, you would create a playbook to ensure Apache is installed, running, and configured properly. When executing the playbook, the steps will be carried out in the specified order to achieve the desired state.
Terraform does things a bit differently. Here, you only need to specify the desired end state, and Terraform will determine the necessary actions to achieve that state. Terraform configurations are written in HCL (Hashicorp Configuration Language), which is similar to JSON. HCL is designed to be easy to read and write, making it straightforward for users to declare resources and their dependencies.
Sticking with the Apache example, in Terraform, you would simply create a configuration file to specify the desired state and necessary resources, which may include an EC2 instance, a VPC, and a security group to allow HTTP traffic. Terraform will then automatically determine the order of operations to create all of the defined resources and manage all dependencies to provision the infrastructure according to the specified state.
With enhanced control over each step, Ansible’s procedural approach is ideal for software deployments that require a sequence of steps, such as configuring files, installing dependencies, or restarting services. One drawback of this approach is its manual nature, making it more time-consuming and prone to error.
Terraform’s declarative approach is more straightforward, focusing on defining the desired end state of the infrastructure rather than detailing each step to get there. This is beneficial in scenarios like scaling resources across different providers. However, it may offer less flexibility for highly specific or conditional workflows compared to Ansible.
3. Different State Management Approaches
State management in the context of IaC is the process of tracking the current state of your infrastructure. The goal with state management is to ensure consistency and reliability, eliminate configuration drift, and simplify changes you want to make.
Ansible operates in a stateless manner, meaning that it doesn’t have native state management. But Ansible can still enforce the desired state effectively. It simply means that Ansible doesn’t have a state file to track the current state of the infrastructure.
That’s why you will rarely hear the term “state management” when speaking about Ansible. You’re more likely to encounter “configuration management.” After all, Ansible relies on its playbooks to define the desired configurations, and enforce them each time the playbook is executed.
On the other hand, the state file is a pivotal component of Terraform. This file contains information about the current state of resources, including their configurations, dependencies, and relationships, and is critical for Terraform to perform its operations accurately.
Terraform also has some nice features to ensure proper state management. State locking prevents multiple users from making changes to the infrastructure at the same time, which may lead to inconsistencies and errors. And with remote state storage, you can store the state file remotely, such as in an S3 bucket, or a Terraform Cloud workspace, which will act as a backup, also enabling better collaboration.
Both tools have viable use cases when it comes to state management. Ansible’s stateless approach works in environments that require quick and flexible configuration management. Conversely, Terraform’s state file and associated features provide a lot of historical tracking capabilities which are advantageous in large teams and collaborative projects.
Conclusion
To sum things up, Ansible’s emphasis on procedural programming and continuous enforcement makes it a strong choice for environments that require granular control and frequent updates. Its stateless nature provides flexibility, though it can be more manual and prone to errors.
Terraform’s declarative approach and robust state management are ideal for large-scale, complex, and multi-cloud deployments. Everything is a bit more automated, which helps with consistency and reduces the risk of errors.
When deciding which tool to use, it’s important to consider the specifics of your environment, and what you’re trying to achieve with the IaC implementation. It’s hard to say that either Ansible or Terraform is better overall, but there are certainly situations where one would make more sense for a specific use case.